    {-# LANGUAGE ViewPatterns #-}

    {-# OPTIONS_GHC -cpp -Wno-incomplete-record-updates #-}

    {-# OPTIONS_GHC -fmax-worker-args=12 #-}
    -- The -fmax-worker-args=12 is there because the main functions
    -- are strict in the OccEnv, and it turned out that with the default settting
    -- some functions would unbox the OccEnv ad some would not, depending on how
    -- many /other/ arguments the function has.  Inconsistent unboxing is very
    -- bad for performance, so I increased the limit to allow it to unbox
    -- consistently.

    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    ************************************************************************
    *                                                                      *
    \section[OccurAnal]{Occurrence analysis pass}
    *                                                                      *
    ************************************************************************

    The occurrence analyser re-typechecks a core expression, returning a new
    core expression with (hopefully) improved usage information.
    -}

    module GHC.Core.Opt.OccurAnal (
        occurAnalysePgm,
        occurAnalyseExpr,
        zapLambdaBndrs, scrutBinderSwap_maybe
      ) where

    import GHC.Prelude hiding ( head, init, last, tail )

    import GHC.Core
    import GHC.Core.FVs
    import GHC.Core.Utils   ( exprIsTrivial, isDefaultAlt, isExpandableApp,
                              mkCastMCo, mkTicks )
    import GHC.Core.Opt.Arity   ( joinRhsArity, isOneShotBndr )
    import GHC.Core.Coercion
    import GHC.Core.Predicate   ( isDictId )
    import GHC.Core.Type
    import GHC.Core.TyCo.FVs    ( tyCoVarsOfMCo )

    import GHC.Data.Maybe( orElse )
    import GHC.Data.Graph.Directed ( SCC(..), Node(..)
                                   , stronglyConnCompFromEdgedVerticesUniq
                                   , stronglyConnCompFromEdgedVerticesUniqR )
    import GHC.Types.Unique
    import GHC.Types.Unique.FM
    import GHC.Types.Unique.Set
    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Types.Basic
    import GHC.Types.Tickish
    import GHC.Types.Var.Set
    import GHC.Types.Var.Env
    import GHC.Types.Var
    import GHC.Types.Demand ( argOneShots, argsOneShots )

    import GHC.Utils.Outputable
    import GHC.Utils.Panic
    import GHC.Utils.Misc

    import GHC.Builtin.Names( runRWKey )
    import GHC.Unit.Module( Module )

    import Data.List (mapAccumL)

    {-
    ************************************************************************
    *                                                                      *
        occurAnalysePgm, occurAnalyseExpr
    *                                                                      *
    ************************************************************************

    Here's the externally-callable interface:
    -}

    -- | Do occurrence analysis, and discard occurrence info returned
    occurAnalyseExpr :: CoreExpr -> CoreExpr
    occurAnalyseExpr :: CoreExpr -> CoreExpr
    occurAnalyseExpr CoreExpr
    expr = CoreExpr
    expr'
      where
        WUD UsageDetails
    _ CoreExpr
    expr' = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    initOccEnv CoreExpr
    expr

    occurAnalysePgm :: Module         -- Used only in debug output
                    -> (Id -> Bool)         -- Active unfoldings
                    -> (Activation -> Bool) -- Active rules
                    -> [CoreRule]           -- Local rules for imported Ids
                    -> CoreProgram -> CoreProgram
    occurAnalysePgm :: Module
    -> (Id -> Bool)
    -> (Activation -> Bool)
    -> [CoreRule]
    -> CoreProgram
    -> CoreProgram
    occurAnalysePgm Module
    this_mod Id -> Bool
    active_unf Activation -> Bool
    active_rule [CoreRule]
    imp_rules CoreProgram
    binds
      | UsageDetails -> Bool
    isEmptyDetails UsageDetails
    final_usage
      = CoreProgram
    occ_anald_binds

      | Bool
    otherwise   -- See Note [Glomming]
      = Bool -> String -> SDoc -> CoreProgram -> CoreProgram
    forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
    warnPprTrace Bool
    True String
    "Glomming in" (SDoc -> JoinArity -> SDoc -> SDoc
    hang (Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    this_mod SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc
    forall doc. IsLine doc => doc
    colon) JoinArity
    2 (UsageDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr UsageDetails
    final_usage))
        CoreProgram
    occ_anald_glommed_binds
      where
        init_env :: OccEnv
    init_env = OccEnv
    initOccEnv { occ_rule_act = active_rule
                              , occ_unf_act  = active_unf }

        WUD UsageDetails
    final_usage CoreProgram
    occ_anald_binds = CoreProgram -> OccEnv -> WithUsageDetails CoreProgram
    go CoreProgram
    binds OccEnv
    init_env
        WUD UsageDetails
    _ CoreProgram
    occ_anald_glommed_binds = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(Id, CoreExpr)]
    -> UsageDetails
    -> WithUsageDetails CoreProgram
    occAnalRecBind OccEnv
    init_env TopLevelFlag
    TopLevel
                                                        ImpRuleEdges
    imp_rule_edges
                                                        (CoreProgram -> [(Id, CoreExpr)]
    forall b. [Bind b] -> [(b, Expr b)]
    flattenBinds CoreProgram
    binds)
                                                        UsageDetails
    initial_uds
              -- It's crucial to re-analyse the glommed-together bindings
              -- so that we establish the right loop breakers. Otherwise
              -- we can easily create an infinite loop (#9583 is an example)
              --
              -- Also crucial to re-analyse the /original/ bindings
              -- in case the first pass accidentally discarded as dead code
              -- a binding that was actually needed (albeit before its
              -- definition site).  #17724 threw this up.

        initial_uds :: UsageDetails
    initial_uds = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    emptyDetails ([CoreRule] -> VarSet
    rulesFreeVars [CoreRule]
    imp_rules)
        -- The RULES declarations keep things alive!

        -- imp_rule_edges maps a top-level local binder 'f' to the
        -- RHS free vars of any IMP-RULE, a local RULE for an imported function,
        -- where 'f' appears on the LHS
        --   e.g.  RULE foldr f = blah
        --         imp_rule_edges contains f :-> fvs(blah)
        -- We treat such RULES as extra rules for 'f'
        -- See Note [Preventing loops due to imported functions rules]
        imp_rule_edges :: ImpRuleEdges
        imp_rule_edges :: ImpRuleEdges
    imp_rule_edges = (ImpRuleEdges -> ImpRuleEdges -> ImpRuleEdges)
    -> ImpRuleEdges -> [ImpRuleEdges] -> ImpRuleEdges
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (([(Activation, VarSet)]
     -> [(Activation, VarSet)] -> [(Activation, VarSet)])
    -> ImpRuleEdges -> ImpRuleEdges -> ImpRuleEdges
    forall a. (a -> a -> a) -> VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv_C [(Activation, VarSet)]
    -> [(Activation, VarSet)] -> [(Activation, VarSet)]
    forall a. [a] -> [a] -> [a]
    (++)) ImpRuleEdges
    forall a. VarEnv a
    emptyVarEnv
                               [ (Id -> [(Activation, VarSet)]) -> VarEnv Id -> ImpRuleEdges
    forall a b. (a -> b) -> VarEnv a -> VarEnv b
    mapVarEnv ([(Activation, VarSet)] -> Id -> [(Activation, VarSet)]
    forall a b. a -> b -> a
    const [(Activation
    act,VarSet
    rhs_fvs)]) (VarEnv Id -> ImpRuleEdges) -> VarEnv Id -> ImpRuleEdges
    forall a b. (a -> b) -> a -> b
    $ VarSet -> VarEnv Id
    forall a. UniqSet a -> UniqFM a a
    getUniqSet (VarSet -> VarEnv Id) -> VarSet -> VarEnv Id
    forall a b. (a -> b) -> a -> b
    $
                                 [CoreExpr] -> VarSet
    exprsFreeIds [CoreExpr]
    args VarSet -> [Id] -> VarSet
    `delVarSetList` [Id]
    bndrs
                               | Rule { ru_act :: CoreRule -> Activation
    ru_act = Activation
    act, ru_bndrs :: CoreRule -> [Id]
    ru_bndrs = [Id]
    bndrs
                                       , ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args, ru_rhs :: CoreRule -> CoreExpr
    ru_rhs = CoreExpr
    rhs } <- [CoreRule]
    imp_rules
                                       -- Not BuiltinRules; see Note [Plugin rules]
                               , let rhs_fvs :: VarSet
    rhs_fvs = CoreExpr -> VarSet
    exprFreeIds CoreExpr
    rhs VarSet -> [Id] -> VarSet
    `delVarSetList` [Id]
    bndrs ]

        go :: [CoreBind] -> OccEnv -> WithUsageDetails [CoreBind]
        go :: CoreProgram -> OccEnv -> WithUsageDetails CoreProgram
    go []           OccEnv
    _   = UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    initial_uds []
        go (CoreBind
    bind:CoreProgram
    binds) OccEnv
    env = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> (OccEnv -> WithUsageDetails CoreProgram)
    -> (CoreProgram -> CoreProgram -> CoreProgram)
    -> WithUsageDetails CoreProgram
    forall r.
    OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> (OccEnv -> WithUsageDetails r)
    -> (CoreProgram -> r -> r)
    -> WithUsageDetails r
    occAnalBind OccEnv
    env TopLevelFlag
    TopLevel
                               ImpRuleEdges
    imp_rule_edges CoreBind
    bind (CoreProgram -> OccEnv -> WithUsageDetails CoreProgram
    go CoreProgram
    binds) CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    (++)

    {- *********************************************************************
    *                                                                      *
                    IMP-RULES
             Local rules for imported functions
    *                                                                      *
    ********************************************************************* -}

    type ImpRuleEdges = IdEnv [(Activation, VarSet)]
        -- Mapping from a local Id 'f' to info about its IMP-RULES,
        -- i.e. /local/ rules for an imported Id that mention 'f' on the LHS
        -- We record (a) its Activation and (b) the RHS free vars
        -- See Note [IMP-RULES: local rules for imported functions]

    noImpRuleEdges :: ImpRuleEdges
    noImpRuleEdges :: ImpRuleEdges
    noImpRuleEdges = ImpRuleEdges
    forall a. VarEnv a
    emptyVarEnv

    lookupImpRules :: ImpRuleEdges -> Id -> [(Activation,VarSet)]
    lookupImpRules :: ImpRuleEdges -> Id -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges Id
    bndr
      = case ImpRuleEdges -> Id -> Maybe [(Activation, VarSet)]
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv ImpRuleEdges
    imp_rule_edges Id
    bndr of
          Maybe [(Activation, VarSet)]
    Nothing -> []
          Just [(Activation, VarSet)]
    vs -> [(Activation, VarSet)]
    vs

    impRulesScopeUsage :: [(Activation,VarSet)] -> UsageDetails
    -- Variable mentioned in RHS of an IMP-RULE for the bndr,
    -- whether active or not
    impRulesScopeUsage :: [(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage [(Activation, VarSet)]
    imp_rules_info
      = ((Activation, VarSet) -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [(Activation, VarSet)] -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (Activation, VarSet) -> UsageDetails -> UsageDetails
    forall {a}. (a, VarSet) -> UsageDetails -> UsageDetails
    add UsageDetails
    emptyDetails [(Activation, VarSet)]
    imp_rules_info
      where
        add :: (a, VarSet) -> UsageDetails -> UsageDetails
    add (a
    _,VarSet
    vs) UsageDetails
    usage = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage VarSet
    vs

    impRulesActiveFvs :: (Activation -> Bool) -> VarSet
                      -> [(Activation,VarSet)] -> VarSet
    impRulesActiveFvs :: (Activation -> Bool) -> VarSet -> [(Activation, VarSet)] -> VarSet
    impRulesActiveFvs Activation -> Bool
    is_active VarSet
    bndr_set [(Activation, VarSet)]
    vs
      = ((Activation, VarSet) -> VarSet -> VarSet)
    -> VarSet -> [(Activation, VarSet)] -> VarSet
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (Activation, VarSet) -> VarSet -> VarSet
    add VarSet
    emptyVarSet [(Activation, VarSet)]
    vs VarSet -> VarSet -> VarSet
    `intersectVarSet` VarSet
    bndr_set
      where
        add :: (Activation, VarSet) -> VarSet -> VarSet
    add (Activation
    act,VarSet
    vs) VarSet
    acc | Activation -> Bool
    is_active Activation
    act = VarSet
    vs VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    acc
                         | Bool
    otherwise     = VarSet
    acc

    {- Note [IMP-RULES: local rules for imported functions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We quite often have
      * A /local/ rule
      * for an /imported/ function
    like this:
      foo x = blah
      {-# RULE "map/foo" forall xs. map foo xs = xs #-}
    We call them IMP-RULES.  They are important in practice, and occur a
    lot in the libraries.

    IMP-RULES are held in mg_rules of ModGuts, and passed in to
    occurAnalysePgm.

    Main Invariant:

    * Throughout, we treat an IMP-RULE that mentions 'f' on its LHS
      just like a RULE for f.

    Note [IMP-RULES: unavoidable loops]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this
       f = /\a. B.g a
       RULE B.g Int = 1 + f Int
    Note that
      * The RULE is for an imported function.
      * f is non-recursive
    Now we
    can get
       f Int --> B.g Int      Inlining f
             --> 1 + f Int    Firing RULE
    and so the simplifier goes into an infinite loop. This
    would not happen if the RULE was for a local function,
    because we keep track of dependencies through rules.  But
    that is pretty much impossible to do for imported Ids.  Suppose
    f's definition had been
       f = /\a. C.h a
    where (by some long and devious process), C.h eventually inlines to
    B.g.  We could only spot such loops by exhaustively following
    unfoldings of C.h etc, in case we reach B.g, and hence (via the RULE)
    f.

    We regard this potential infinite loop as a *programmer* error.
    It's up the programmer not to write silly rules like
         RULE f x = f x
    and the example above is just a more complicated version.

    Note [Specialising imported functions] (referred to from Specialise)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For *automatically-generated* rules, the programmer can't be
    responsible for the "programmer error" in Note [IMP-RULES: unavoidable
    loops].  In particular, consider specialising a recursive function
    defined in another module.  If we specialise a recursive function B.g,
    we get
      g_spec = .....(B.g Int).....
      RULE B.g Int = g_spec
    Here, g_spec doesn't look recursive, but when the rule fires, it
    becomes so.  And if B.g was mutually recursive, the loop might not be
    as obvious as it is here.

    To avoid this,
     * When specialising a function that is a loop breaker,
       give a NOINLINE pragma to the specialised function

    Note [Preventing loops due to imported functions rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider:
      import GHC.Base (foldr)

      {-# RULES "filterList" forall p. foldr (filterFB (:) p) [] = filter p #-}
      filter p xs = build (\c n -> foldr (filterFB c p) n xs)
      filterFB c p = ...

      f = filter p xs

    Note that filter is not a loop-breaker, so what happens is:
      f =          filter p xs
        = {inline} build (\c n -> foldr (filterFB c p) n xs)
        = {inline} foldr (filterFB (:) p) [] xs
        = {RULE}   filter p xs

    We are in an infinite loop.

    A more elaborate example (that I actually saw in practice when I went to
    mark GHC.List.filter as INLINABLE) is as follows. Say I have this module:
      {-# LANGUAGE RankNTypes #-}
      module GHCList where

      import Prelude hiding (filter)
      import GHC.Base (build)

      {-# INLINABLE filter #-}
      filter :: (a -> Bool) -> [a] -> [a]
      filter p [] = []
      filter p (x:xs) = if p x then x : filter p xs else filter p xs

      {-# NOINLINE [0] filterFB #-}
      filterFB :: (a -> b -> b) -> (a -> Bool) -> a -> b -> b
      filterFB c p x r | p x       = x `c` r
                       | otherwise = r

      {-# RULES
      "filter"     [~1] forall p xs.  filter p xs = build (\c n -> foldr
      (filterFB c p) n xs)
      "filterList" [1]  forall p.     foldr (filterFB (:) p) [] = filter p
       #-}

    Then (because RULES are applied inside INLINABLE unfoldings, but inlinings
    are not), the unfolding given to "filter" in the interface file will be:
      filter p []     = []
      filter p (x:xs) = if p x then x : build (\c n -> foldr (filterFB c p) n xs)
                               else     build (\c n -> foldr (filterFB c p) n xs

    Note that because this unfolding does not mention "filter", filter is not
    marked as a strong loop breaker. Therefore at a use site in another module:
      filter p xs
        = {inline}
          case xs of []     -> []
                     (x:xs) -> if p x then x : build (\c n -> foldr (filterFB c p) n xs)
                                      else     build (\c n -> foldr (filterFB c p) n xs)

      build (\c n -> foldr (filterFB c p) n xs)
        = {inline} foldr (filterFB (:) p) [] xs
        = {RULE}   filter p xs

    And we are in an infinite loop again, except that this time the loop is producing an
    infinitely large *term* (an unrolling of filter) and so the simplifier finally
    dies with "ticks exhausted"

    SOLUTION: we treat the rule "filterList" as an extra rule for 'filterFB'
    because it mentions 'filterFB' on the LHS.  This is the Main Invariant
    in Note [IMP-RULES: local rules for imported functions].

    So, during loop-breaker analysis:

    - for each active RULE for a local function 'f' we add an edge between
      'f' and the local FVs of the rule RHS

    - for each active RULE for an *imported* function we add dependency
      edges between the *local* FVS of the rule LHS and the *local* FVS of
      the rule RHS.

    Even with this extra hack we aren't always going to get things
    right. For example, it might be that the rule LHS mentions an imported
    Id, and another module has a RULE that can rewrite that imported Id to
    one of our local Ids.

    Note [Plugin rules]
    ~~~~~~~~~~~~~~~~~~~
    Conal Elliott (#11651) built a GHC plugin that added some
    BuiltinRules (for imported Ids) to the mg_rules field of ModGuts, to
    do some domain-specific transformations that could not be expressed
    with an ordinary pattern-matching CoreRule.  But then we can't extract
    the dependencies (in imp_rule_edges) from ru_rhs etc, because a
    BuiltinRule doesn't have any of that stuff.

    So we simply assume that BuiltinRules have no dependencies, and filter
    them out from the imp_rule_edges comprehension.

    Note [Glomming]
    ~~~~~~~~~~~~~~~
    RULES for imported Ids can make something at the top refer to
    something at the bottom:

            foo = ...(B.f @Int)...
            $sf = blah
            RULE:  B.f @Int = $sf

    Applying this rule makes foo refer to $sf, although foo doesn't appear to
    depend on $sf.  (And, as in Note [IMP-RULES: local rules for imported functions], the
    dependency might be more indirect. For example, foo might mention C.t
    rather than B.f, where C.t eventually inlines to B.f.)

    NOTICE that this cannot happen for rules whose head is a
    locally-defined function, because we accurately track dependencies
    through RULES.  It only happens for rules whose head is an imported
    function (B.f in the example above).

    Solution:
      - When simplifying, bring all top level identifiers into
        scope at the start, ignoring the Rec/NonRec structure, so
        that when 'h' pops up in f's rhs, we find it in the in-scope set
        (as the simplifier generally expects). This happens in simplTopBinds.

      - In the occurrence analyser, if there are any out-of-scope
        occurrences that pop out of the top, which will happen after
        firing the rule:      f = \x -> h x
                              h = \y -> 3
        then just glom all the bindings into a single Rec, so that
        the *next* iteration of the occurrence analyser will sort
        them all out.   This part happens in occurAnalysePgm.

    This is a legitimate situation where the need for glomming doesn't
    point to any problems. However, when GHC is compiled with -DDEBUG, we
    produce a warning addressed to the GHC developers just in case we
    require glomming due to an out-of-order reference that is caused by
    some earlier transformation stage misbehaving.
    -}

    {-
    ************************************************************************
    *                                                                      *
                    Bindings
    *                                                                      *
    ************************************************************************

    Note [Recursive bindings: the grand plan]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Loop breaking is surprisingly subtle.  First read the section 4 of
    "Secrets of the GHC inliner".  This describes our basic plan.  We
    avoid infinite inlinings by choosing loop breakers, and ensuring that
    a loop breaker cuts each loop.

    See also Note [Inlining and hs-boot files] in GHC.Core.ToIface, which
    deals with a closely related source of infinite loops.

    When we come across a binding group
      Rec { x1 = r1; ...; xn = rn }
    we treat it like this (occAnalRecBind):

    1. Note [Forming Rec groups]
       Occurrence-analyse each right hand side, and build a
       "Details" for each binding to capture the results.
       Wrap the details in a LetrecNode, ready for SCC analysis.
       All this is done by makeNode.

       The edges of this graph are the "scope edges".

    2. Do SCC-analysis on these Nodes:
       - Each CyclicSCC will become a new Rec
       - Each AcyclicSCC will become a new NonRec

       The key property is that every free variable of a binding is
       accounted for by the scope edges, so that when we are done
       everything is still in scope.

    3. For each AcyclicSCC, just make a NonRec binding.

    4. For each CyclicSCC of the scope-edge SCC-analysis in (2), we
       identify suitable loop-breakers to ensure that inlining terminates.
       This is done by occAnalRec.

       To do so, form the loop-breaker graph, do SCC analysis. For each
       CyclicSCC we choose a loop breaker, delete all edges to that node,
       re-analyse the SCC, and iterate. See Note [Choosing loop breakers]
       for the details

    Note [Dead code]
    ~~~~~~~~~~~~~~~~
    Dropping dead code for a cyclic Strongly Connected Component is done
    in a very simple way:

            the entire SCC is dropped if none of its binders are mentioned
            in the body; otherwise the whole thing is kept.

    The key observation is that dead code elimination happens after
    dependency analysis: so 'occAnalBind' processes SCCs instead of the
    original term's binding groups.

    Thus 'occAnalBind' does indeed drop 'f' in an example like

            letrec f = ...g...
                   g = ...(...g...)...
            in
               ...g...

    when 'g' no longer uses 'f' at all (eg 'f' does not occur in a RULE in
    'g'). 'occAnalBind' first consumes 'CyclicSCC g' and then it consumes
    'AcyclicSCC f', where 'body_usage' won't contain 'f'.

    Note [Forming Rec groups]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    The key point about the "Forming Rec groups" step is that it /preserves
    scoping/.  If 'x' is mentioned, it had better be bound somewhere.  So if
    we start with
      Rec { f = ...h...
          ; g = ...f...
          ; h = ...f... }
    we can split into SCCs
      Rec { f = ...h...
          ; h = ..f... }
      NonRec { g = ...f... }

    We put bindings {f = ef; g = eg } in a Rec group if "f uses g" and "g
    uses f", no matter how indirectly.  We do a SCC analysis with an edge
    f -> g if "f mentions g". That is, g is free in:
      a) the rhs 'ef'
      b) or the RHS of a rule for f, whether active or inactive
           Note [Rules are extra RHSs]
      c) or the LHS or a rule for f, whether active or inactive
           Note [Rule dependency info]
      d) the RHS of an /active/ local IMP-RULE
           Note [IMP-RULES: local rules for imported functions]

    (b) and (c) apply regardless of the activation of the RULE, because even if
    the rule is inactive its free variables must be bound.  But (d) doesn't need
    to worry about this because IMP-RULES are always notionally at the bottom
    of the file.

      * Note [Rules are extra RHSs]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~
        A RULE for 'f' is like an extra RHS for 'f'. That way the "parent"
        keeps the specialised "children" alive.  If the parent dies
        (because it isn't referenced any more), then the children will die
        too (unless they are already referenced directly).

        So in Example [eftInt], eftInt and eftIntFB will be put in the
        same Rec, even though their 'main' RHSs are both non-recursive.

        We must also include inactive rules, so that their free vars
        remain in scope.

      * Note [Rule dependency info]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~
        The VarSet in a RuleInfo is used for dependency analysis in the
        occurrence analyser.  We must track free vars in *both* lhs and rhs.
        Hence use of idRuleVars, rather than idRuleRhsVars in occAnalBind.
        Why both? Consider
            x = y
            RULE f x = v+4
        Then if we substitute y for x, we'd better do so in the
        rule's LHS too, so we'd better ensure the RULE appears to mention 'x'
        as well as 'v'

      * Note [Rules are visible in their own rec group]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        We want the rules for 'f' to be visible in f's right-hand side.
        And we'd like them to be visible in other functions in f's Rec
        group.  E.g. in Note [Specialisation rules] we want f' rule
        to be visible in both f's RHS, and fs's RHS.

        This means that we must simplify the RULEs first, before looking
        at any of the definitions.  This is done by Simplify.simplRecBind,
        when it calls addLetIdInfo.

    Note [TailUsageDetails when forming Rec groups]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The `TailUsageDetails` stored in the `nd_uds` field of a `NodeDetails` is
    computed by `occAnalLamTail` applied to the RHS, not `occAnalExpr`.
    That is because the binding might still become a *non-recursive join point* in
    the AcyclicSCC case of dependency analysis!
    Hence we do the delayed `adjustTailUsage` in `occAnalRec`/`tagRecBinders` to get
    a regular, adjusted UsageDetails.
    See Note [Join points and unfoldings/rules] for more details on the contract.

    Note [Stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    None of the above stuff about RULES applies to a stable unfolding
    stored in a CoreUnfolding.  The unfolding, if any, is simplified
    at the same time as the regular RHS of the function (ie *not* like
    Note [Rules are visible in their own rec group]), so it should be
    treated *exactly* like an extra RHS.

    Or, rather, when computing loop-breaker edges,
      * If f has an INLINE pragma, and it is active, we treat the
        INLINE rhs as f's rhs
      * If it's inactive, we treat f as having no rhs
      * If it has no INLINE pragma, we look at f's actual rhs

    There is a danger that we'll be sub-optimal if we see this
         f = ...f...
         [INLINE f = ..no f...]
    where f is recursive, but the INLINE is not. This can just about
    happen with a sufficiently odd set of rules; eg

            foo :: Int -> Int
            {-# INLINE [1] foo #-}
            foo x = x+1

            bar :: Int -> Int
            {-# INLINE [1] bar #-}
            bar x = foo x + 1

            {-# RULES "foo" [~1] forall x. foo x = bar x #-}

    Here the RULE makes bar recursive; but it's INLINE pragma remains
    non-recursive. It's tempting to then say that 'bar' should not be
    a loop breaker, but an attempt to do so goes wrong in two ways:
       a) We may get
             $df = ...$cfoo...
             $cfoo = ...$df....
             [INLINE $cfoo = ...no-$df...]
          But we want $cfoo to depend on $df explicitly so that we
          put the bindings in the right order to inline $df in $cfoo
          and perhaps break the loop altogether.  (Maybe this
       b)

    Example [eftInt]
    ~~~~~~~~~~~~~~~
    Example (from GHC.Enum):

      eftInt :: Int# -> Int# -> [Int]
      eftInt x y = ...(non-recursive)...

      {-# INLINE [0] eftIntFB #-}
      eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
      eftIntFB c n x y = ...(non-recursive)...

      {-# RULES
      "eftInt"  [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
      "eftIntList"  [1] eftIntFB  (:) [] = eftInt
       #-}

    Note [Specialisation rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this group, which is typical of what SpecConstr builds:

       fs a = ....f (C a)....
       f  x = ....f (C a)....
       {-# RULE f (C a) = fs a #-}

    So 'f' and 'fs' are in the same Rec group (since f refers to fs via its RULE).

    But watch out!  If 'fs' is not chosen as a loop breaker, we may get an infinite loop:
      - the RULE is applied in f's RHS (see Note [Rules for recursive functions] in GHC.Core.Opt.Simplify
      - fs is inlined (say it's small)
      - now there's another opportunity to apply the RULE

    This showed up when compiling Control.Concurrent.Chan.getChanContents.
    Hence the transitive rule_fv_env stuff described in
    Note [Rules and loop breakers].

    Note [Occurrence analysis for join points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider these two somewhat artificial programs (#22404)

      Program (P1)                      Program (P2)
      ------------------------------    -------------------------------------
      let v = <small thunk> in          let v = <small thunk> in
                                        join j = case v of (a,b) -> a
      in case x of                      in case x of
            A -> case v of (a,b) -> a         A -> j
            B -> case v of (a,b) -> a         B -> j
            C -> case v of (a,b) -> b         C -> case v of (a,b) -> b
            D -> []                           D -> []

    In (P1), `v` gets allocated, as a thunk, every time this code is executed.  But
    notice that `v` occurs at most once in any case branch; the occurrence analyser
    spots this and returns a OneOcc{ occ_n_br = 3 } for `v`.  Then the code in
    GHC.Core.Opt.Simplify.Utils.postInlineUnconditionally inlines `v` at its three
    use sites, and discards the let-binding.  That way, we avoid allocating `v` in
    the A,B,C branches (though we still compute it of course), and branch D
    doesn't involve <small thunk> at all.  This sometimes makes a Really Big
    Difference.

    In (P2) we have shared the common RHS of A, B, in a join point `j`.  We would
    like to inline `v` in just the same way as in (P1).  But the usual strategy
    for let bindings is conservative and uses `andUDs` to combine usage from j's
    RHS to its body; as if `j` was called on every code path (once, albeit).  In
    the case of (P2), we'll get ManyOccs for `v`.  Important optimisation lost!

    Solving this problem makes the Simplifier less fragile.  For example,
    the Simplifier might inline `j`, and convert (P2) into (P1)... or it might
    not, depending in a perhaps-fragile way on the size of the join point.
    I was motivated to implement this feature of the occurrence analyser
    when trying to make optimisation join points simpler and more robust
    (see e.g. #23627).

    The occurrence analyser therefore has clever code that behaves just as
    if you inlined `j` at all its call sites.  Here is a tricky variant
    to keep in mind:

      Program (P3)
      -------------------------------
        join j = case v of (a,b) -> a
        in case f v of
              A -> j
              B -> j
              C -> []

    If you mentally inline `j` you'll see that `v` is used twice on the path
    through A, so it should have ManyOcc.  Bear this case in mind!

    * We treat /non-recursive/ join points specially. Recursive join points are
      treated like any other letrec, as before.  Moreover, we only give this special
      treatment to /pre-existing/ non-recursive join points, not the ones that we
      discover for the first time in this sweep of the occurrence analyser.

    * In occ_env, the new (occ_join_points :: IdEnv OccInfoEnv) maps
      each in-scope non-recursive join point, such as `j` above, to
      a "zeroed form" of its RHS's usage details. The "zeroed form"
        * deletes ManyOccs
        * maps a OneOcc to OneOcc{ occ_n_br = 0 }
      In our example, occ_join_points will be extended with
          [j :-> [v :-> OneOcc{occ_n_br=0}]]
      See addJoinPoint.

    * At an occurrence of a join point, we do everything as normal, but add in the
      UsageDetails from the occ_join_points.  See mkOneOcc.

    * Crucially, at the NonRec binding of the join point, in `occAnalBind`, we use
      `orUDs`, not `andUDs` to combine the usage from the RHS with the usage from
      the body.

    Here are the consequences

    * Because of the perhaps-surprising OneOcc{occ_n_br=0} idea of the zeroed
      form, the occ_n_br field of a OneOcc binder still counts the number of
      /actual lexical occurrences/ of the variable.  In Program P2, for example,
      `v` will end up with OneOcc{occ_n_br=2}, not occ_n_br=3.
      There are two lexical occurrences of `v`!
      (NB: `orUDs` adds occ_n_br together, so occ_n_br=1 is impossible, too.)

    * In the tricky (P3) we'll get an `andUDs` of
        * OneOcc{occ_n_br=0} from the occurrences of `j`)
        * OneOcc{occ_n_br=1} from the (f v)
      These are `andUDs` together in `addOccInfo`, and hence
      `v` gets ManyOccs, just as it should.  Clever!

    There are a couple of tricky wrinkles

    (W1) Consider this example which shadows `j`:
              join j = rhs in
              in case x of { K j -> ..j..; ... }
         Clearly when we come to the pattern `K j` we must drop the `j`
         entry in occ_join_points.

         This is done by `drop_shadowed_joins` in `addInScope`.

    (W2) Consider this example which shadows `v`:
              join j = ...v...
              in case x of { K v -> ..j..; ... }

         We can't make j's occurrences in the K alternative give rise to an
         occurrence of `v` (via occ_join_points), because it'll just be deleted by
         the `K v` pattern.  Yikes.  This is rare because shadowing is rare, but
         it definitely can happen.  Solution: when bringing `v` into scope at
         the `K v` pattern, chuck out of occ_join_points any elements whose
         UsageDetails mentions `v`.  Instead, just `andUDs` all that usage in
         right here.

         This requires work in two places.
         * In `preprocess_env`, we detect if the newly-bound variables intersect
           the free vars of occ_join_points.  (These free vars are conveniently
           simply the domain of the OccInfoEnv for that join point.) If so,
           we zap the entire occ_join_points.
         * In `postprcess_uds`, we add the chucked-out join points to the
           returned UsageDetails, with `andUDs`.

    (W3) Consider this example, which shadows `j`, but this time in an argument
                  join j = rhs
                  in f (case x of { K j -> ...; ... })
         We can zap the entire occ_join_points when looking at the argument,
         because `j` can't posibly occur -- it's a join point!  And the smaller
         occ_join_points is, the better.  Smaller to look up in mkOneOcc, and
         more important, less looking-up when checking (W2).

         This is done in setNonTailCtxt.  It's important /not/ to do this for
         join-point RHS's because of course `j` can occur there!

         NB: this is just about efficiency: it is always safe /not/ to zap the
         occ_join_points.

    (W4) What if the join point binding has a stable unfolding, or RULES?
         They are just alternative right-hand sides, and at each call site we
         will use only one of them. So again, we can use `orUDs` to combine
         usage info from all these alternatives RHSs.

    Wrinkles (W1) and (W2) are very similar to Note [Binder swap] (BS3).

    Note [Finding join points]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's the occurrence analyser's job to find bindings that we can turn into join
    points, but it doesn't perform that transformation right away. Rather, it marks
    the eligible bindings as part of their occurrence data, leaving it to the
    simplifier (or to simpleOptPgm) to actually change the binder's 'IdDetails'.
    The simplifier then eta-expands the RHS if needed and then updates the
    occurrence sites. Dividing the work this way means that the occurrence analyser
    still only takes one pass, yet one can always tell the difference between a
    function call and a jump by looking at the occurrence (because the same pass
    changes the 'IdDetails' and propagates the binders to their occurrence sites).

    To track potential join points, we use the 'occ_tail' field of OccInfo. A value
    of `AlwaysTailCalled n` indicates that every occurrence of the variable is a
    tail call with `n` arguments (counting both value and type arguments). Otherwise
    'occ_tail' will be 'NoTailCallInfo'. The tail call info flows bottom-up with the
    rest of 'OccInfo' until it goes on the binder.

    Note [Join arity prediction based on joinRhsArity]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In general, the join arity from tail occurrences of a join point (O) may be
    higher or lower than the manifest join arity of the join body (M). E.g.,

      -- M > O:
      let f x y = x + y              -- M = 2
      in if b then f 1 else f 2      -- O = 1
      ==> { Contify for join arity 1 }
      join f x = \y -> x + y
      in if b then jump f 1 else jump f 2

      -- M < O
      let f = id                     -- M = 0
      in if ... then f 12 else f 13  -- O = 1
      ==> { Contify for join arity 1, eta-expand f }
      join f x = id x
      in if b then jump f 12 else jump f 13

    But for *recursive* let, it is crucial that both arities match up, consider

      letrec f x y = if ... then f x else True
      in f 42

    Here, M=2 but O=1. If we settled for a joinrec arity of 1, the recursive jump
    would not happen in a tail context! Contification is invalid here.
    So indeed it is crucial to demand that M=O.

    (Side note: Actually, we could be more specific: Let O1 be the join arity of
    occurrences from the letrec RHS and O2 the join arity from the let body. Then
    we need M=O1 and M<=O2 and could simply eta-expand the RHS to match O2 later.
    M=O is the specific case where we don't want to eta-expand. Neither the join
    points paper nor GHC does this at the moment.)

    We can capitalise on this observation and conclude that *if* f could become a
    joinrec (without eta-expansion), it will have join arity M.
    Now, M is just the result of 'joinRhsArity', a rather simple, local analysis.
    It is also the join arity inside the 'TailUsageDetails' returned by
    'occAnalLamTail', so we can predict join arity without doing any fixed-point
    iteration or really doing any deep traversal of let body or RHS at all.
    We check for M in the 'adjustTailUsage' call inside 'tagRecBinders'.

    All this is quite apparent if you look at the contification transformation in
    Fig. 5 of "Compiling without Continuations" (which does not account for
    eta-expansion at all, mind you). The letrec case looks like this

      letrec f = /\as.\xs. L[us] in L'[es]
        ... and a bunch of conditions establishing that f only occurs
            in app heads of join arity (len as + len xs) inside us and es ...

    The syntactic form `/\as.\xs. L[us]` forces M=O iff `f` occurs in `us`. However,
    for non-recursive functions, this is the definition of contification from the
    paper:

      let f = /\as.\xs.u in L[es]     ... conditions ...

    Note that u could be a lambda itself, as we have seen. No relationship between M
    and O to exploit here.

    Note [Join points and unfoldings/rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       let j2 y = blah
       let j x = j2 (x+x)
           {-# INLINE [2] j #-}
       in case e of { A -> j 1; B -> ...; C -> j 2 }

    Before j is inlined, we'll have occurrences of j2 in
    both j's RHS and in its stable unfolding.  We want to discover
    j2 as a join point. So 'occAnalUnfolding' returns an unadjusted
    'TailUsageDetails', like 'occAnalLamTail'. We adjust the usage details of the
    unfolding to the actual join arity using the same 'adjustTailArity' as for
    the RHS, see Note [Adjusting right-hand sides].

    Same with rules. Suppose we have:

      let j :: Int -> Int
          j y = 2 * y
      let k :: Int -> Int -> Int
          {-# RULES "SPEC k 0" k 0 y = j y #-}
          k x y = x + 2 * y
      in case e of { A -> k 1 2; B -> k 3 5; C -> blah }

    We identify k as a join point, and we want j to be a join point too.
    Without the RULE it would be, and we don't want the RULE to mess it
    up.  So provided the join-point arity of k matches the args of the
    rule we can allow the tail-call info from the RHS of the rule to
    propagate.

    * Note that the join arity of the RHS and that of the unfolding or RULE might
      mismatch:

        let j x y = j2 (x+x)
            {-# INLINE[2] j = \x. g #-}
            {-# RULE forall x y z. j x y z = h 17 #-}
        in j 1 2

      So it is crucial that we adjust each TailUsageDetails individually
      with the actual join arity 2 here before we combine with `andUDs`.
      Here, that means losing tail call info on `g` and `h`.

    * Wrinkle for Rec case: We store one TailUsageDetails in the node Details for
      RHS, unfolding and RULE combined. Clearly, if they don't agree on their join
      arity, we have to do some adjusting. We choose to adjust to the join arity
      of the RHS, because that is likely the join arity that the join point will
      have; see Note [Join arity prediction based on joinRhsArity].

      If the guess is correct, then tail calls in the RHS are preserved; a necessary
      condition for the whole binding becoming a joinrec.
      The guess can only be incorrect in the 'AcyclicSCC' case when the binding
      becomes a non-recursive join point with a different join arity. But then the
      eventual call to 'adjustTailUsage' in 'tagRecBinders'/'occAnalRec' will
      be with a different join arity and destroy unsound tail call info with
      'markNonTail'.

    * Wrinkle for RULES.  Suppose the example was a bit different:
          let j :: Int -> Int
              j y = 2 * y
              k :: Int -> Int -> Int
              {-# RULES "SPEC k 0" k 0 = j #-}
              k x y = x + 2 * y
          in ...
      If we eta-expanded the rule all would be well, but as it stands the
      one arg of the rule don't match the join-point arity of 2.

      Conceivably we could notice that a potential join point would have
      an "undersaturated" rule and account for it. This would mean we
      could make something that's been specialised a join point, for
      instance. But local bindings are rarely specialised, and being
      overly cautious about rules only costs us anything when, for some `j`:

      * Before specialisation, `j` has non-tail calls, so it can't be a join point.
      * During specialisation, `j` gets specialised and thus acquires rules.
      * Sometime afterward, the non-tail calls to `j` disappear (as dead code, say),
        and so now `j` *could* become a join point.

      This appears to be very rare in practice. TODO Perhaps we should gather
      statistics to be sure.

    ------------------------------------------------------------
    Note [Adjusting right-hand sides]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    There's a bit of a dance we need to do after analysing a lambda expression or
    a right-hand side. In particular, we need to

      a) call 'markAllNonTail' *unless* the binding is for a join point, and
         the TailUsageDetails from the RHS has the right join arity; e.g.
            join j x y = case ... of
                           A -> j2 p
                           B -> j2 q
            in j a b
         Here we want the tail calls to j2 to be tail calls of the whole expression
      b) call 'markAllInsideLam' *unless* the binding is for a thunk, a one-shot
         lambda, or a non-recursive join point

    Some examples, with how the free occurrences in e (assumed not to be a value
    lambda) get marked:

                                 inside lam    non-tail-called
      ------------------------------------------------------------
      let x = e                  No            Yes
      let f = \x -> e            Yes           Yes
      let f = \x{OneShot} -> e   No            Yes
      \x -> e                    Yes           Yes
      join j x = e               No            No
      joinrec j x = e            Yes           No

    There are a few other caveats; most importantly, if we're marking a binding as
    'AlwaysTailCalled', it's *going* to be a join point, so we treat it as one so
    that the effect cascades properly. Consequently, at the time the RHS is
    analysed, we won't know what adjustments to make; thus 'occAnalLamTail' must
    return the unadjusted 'TailUsageDetails', to be adjusted by 'adjustTailUsage'
    once join-point-hood has been decided and eventual one-shot annotations have
    been added through 'markNonRecJoinOneShots'.

    It is not so simple to see that 'occAnalNonRecBind' and 'occAnalRecBind' indeed
    perform a similar sequence of steps. Thus, here is an interleaving of events
    of both functions, serving as a specification:

      1. Call 'occAnalLamTail' to find usage information for the RHS.
         Recursive case:     'makeNode'
         Non-recursive case: 'occAnalNonRecBind'
      2. (Analyse the binding's scope. Done in 'occAnalBind'/`occAnal Let{}`.
          Same whether recursive or not.)
      3. Call 'tagNonRecBinder' or 'tagRecBinders', which decides whether to make
         the binding a join point.
         Cyclic  Recursive case:  'mkLoopBreakerNodes'
         Acyclic Recursive case:  `occAnalRec AcyclicSCC{}`
         Non-recursive case:      'occAnalNonRecBind'
      4. Non-recursive join point: Call 'markNonRecJoinOneShots' so that e.g.,
         FloatOut sees one-shot annotations on lambdas
         Acyclic Recursive case:  `occAnalRec AcyclicSCC{}`  calls 'adjustNonRecRhs'
         Non-recursive case:      'occAnalNonRecBind'        calls 'adjustNonRecRhs'
      5. Call 'adjustTailUsage' accordingly.
         Cyclic Recursive case:   'tagRecBinders'
         Acyclic Recursive case:  'adjustNonRecRhs'
         Non-recursive case:      'adjustNonRecRhs'
    -}

    ------------------------------------------------------------------
    --                 occAnalBind
    ------------------------------------------------------------------

    occAnalBind
      :: OccEnv
      -> TopLevelFlag
      -> ImpRuleEdges
      -> CoreBind
      -> (OccEnv -> WithUsageDetails r)  -- Scope of the bind
      -> ([CoreBind] -> r -> r)          -- How to combine the scope with new binds
      -> WithUsageDetails r              -- Of the whole let(rec)

    occAnalBind :: forall r.
    OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> (OccEnv -> WithUsageDetails r)
    -> (CoreProgram -> r -> r)
    -> WithUsageDetails r
    occAnalBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    ire (Rec [(Id, CoreExpr)]
    pairs) OccEnv -> WithUsageDetails r
    thing_inside CoreProgram -> r -> r
    combine
      = OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails r) -> WithUsageDetails r
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env (((Id, CoreExpr) -> Id) -> [(Id, CoreExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, CoreExpr)]
    pairs) ((OccEnv -> WithUsageDetails r) -> WithUsageDetails r)
    -> (OccEnv -> WithUsageDetails r) -> WithUsageDetails r
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
        let WUD UsageDetails
    body_uds r
    body'  = OccEnv -> WithUsageDetails r
    thing_inside OccEnv
    env
            WUD UsageDetails
    bind_uds CoreProgram
    binds' = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(Id, CoreExpr)]
    -> UsageDetails
    -> WithUsageDetails CoreProgram
    occAnalRecBind OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    ire [(Id, CoreExpr)]
    pairs UsageDetails
    body_uds
        in UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    bind_uds (CoreProgram -> r -> r
    combine CoreProgram
    binds' r
    body')

    occAnalBind !OccEnv
    env TopLevelFlag
    lvl ImpRuleEdges
    ire (NonRec Id
    bndr CoreExpr
    rhs) OccEnv -> WithUsageDetails r
    thing_inside CoreProgram -> r -> r
    combine
      | Id -> Bool
    isTyVar Id
    bndr      -- A type let; we don't gather usage info
      = let !(WUD UsageDetails
    body_uds r
    res) = OccEnv
    -> Id -> (OccEnv -> WithUsageDetails r) -> WithUsageDetails r
    forall a.
    OccEnv
    -> Id -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeOne OccEnv
    env Id
    bndr OccEnv -> WithUsageDetails r
    thing_inside
        in UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_uds (CoreProgram -> r -> r
    combine [Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    bndr CoreExpr
    rhs] r
    res)

      -- /Existing/ non-recursive join points
      -- See Note [Occurrence analysis for join points]
      | mb_join :: JoinPointHood
    mb_join@(JoinPoint {}) <- Id -> JoinPointHood
    idJoinPointHood Id
    bndr
      = -- Analyse the RHS and /then/ the body
        let -- Analyse the rhs first, generating rhs_uds
            !([UsageDetails]
    rhs_uds_s, Id
    bndr', CoreExpr
    rhs') = OccEnv
    -> ImpRuleEdges
    -> JoinPointHood
    -> Id
    -> CoreExpr
    -> ([UsageDetails], Id, CoreExpr)
    occAnalNonRecRhs OccEnv
    env ImpRuleEdges
    ire JoinPointHood
    mb_join Id
    bndr CoreExpr
    rhs
            rhs_uds :: UsageDetails
    rhs_uds = (UsageDetails -> UsageDetails -> UsageDetails)
    -> [UsageDetails] -> UsageDetails
    forall a. (a -> a -> a) -> [a] -> a
    forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a
    foldr1 UsageDetails -> UsageDetails -> UsageDetails
    orUDs [UsageDetails]
    rhs_uds_s   -- NB: orUDs.  See (W4) of
                                               -- Note [Occurrence analysis for join points]

            -- Now analyse the body, adding the join point
            -- into the environment with addJoinPoint
            !(WUD UsageDetails
    body_uds (OccInfo
    occ, r
    body)) = OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails r)
    -> WithUsageDetails (OccInfo, r)
    forall r.
    OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails r)
    -> WithUsageDetails (OccInfo, r)
    occAnalNonRecBody OccEnv
    env Id
    bndr' ((OccEnv -> WithUsageDetails r) -> WithUsageDetails (OccInfo, r))
    -> (OccEnv -> WithUsageDetails r) -> WithUsageDetails (OccInfo, r)
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
                                          OccEnv -> WithUsageDetails r
    thing_inside (OccEnv -> Id -> UsageDetails -> OccEnv
    addJoinPoint OccEnv
    env Id
    bndr' UsageDetails
    rhs_uds)
        in
        if OccInfo -> Bool
    isDeadOcc OccInfo
    occ     -- Drop dead code; see Note [Dead code]
        then UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_uds r
    body
        else UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails
    rhs_uds UsageDetails -> UsageDetails -> UsageDetails
    `orUDs` UsageDetails
    body_uds)    -- Note `orUDs`
                 (CoreProgram -> r -> r
    combine [Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec ((Id, JoinPointHood) -> Id
    forall a b. (a, b) -> a
    fst (TopLevelFlag -> OccInfo -> Id -> (Id, JoinPointHood)
    tagNonRecBinder TopLevelFlag
    lvl OccInfo
    occ Id
    bndr')) CoreExpr
    rhs']
                          r
    body)

      -- The normal case, including newly-discovered join points
      -- Analyse the body and /then/ the RHS
      | WUD UsageDetails
    body_uds (OccInfo
    occ,r
    body) <- OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails r)
    -> WithUsageDetails (OccInfo, r)
    forall r.
    OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails r)
    -> WithUsageDetails (OccInfo, r)
    occAnalNonRecBody OccEnv
    env Id
    bndr OccEnv -> WithUsageDetails r
    thing_inside
      = if OccInfo -> Bool
    isDeadOcc OccInfo
    occ   -- Drop dead code; see Note [Dead code]
        then UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_uds r
    body
        else let
            -- Get the join info from the *new* decision; NB: bndr is not already a JoinId
            -- See Note [Join points and unfoldings/rules]
            -- => join arity O of Note [Join arity prediction based on joinRhsArity]
            (Id
    tagged_bndr, JoinPointHood
    mb_join) = TopLevelFlag -> OccInfo -> Id -> (Id, JoinPointHood)
    tagNonRecBinder TopLevelFlag
    lvl OccInfo
    occ Id
    bndr

            !([UsageDetails]
    rhs_uds_s, Id
    final_bndr, CoreExpr
    rhs') = OccEnv
    -> ImpRuleEdges
    -> JoinPointHood
    -> Id
    -> CoreExpr
    -> ([UsageDetails], Id, CoreExpr)
    occAnalNonRecRhs OccEnv
    env ImpRuleEdges
    ire JoinPointHood
    mb_join Id
    tagged_bndr CoreExpr
    rhs
        in UsageDetails -> r -> WithUsageDetails r
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD ((UsageDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [UsageDetails] -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr UsageDetails -> UsageDetails -> UsageDetails
    andUDs UsageDetails
    body_uds [UsageDetails]
    rhs_uds_s)      -- Note `andUDs`
               (CoreProgram -> r -> r
    combine [Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    final_bndr CoreExpr
    rhs'] r
    body)

    -----------------
    occAnalNonRecBody :: OccEnv -> Id
                      -> (OccEnv -> WithUsageDetails r)  -- Scope of the bind
                      -> (WithUsageDetails (OccInfo, r))
    occAnalNonRecBody :: forall r.
    OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails r)
    -> WithUsageDetails (OccInfo, r)
    occAnalNonRecBody OccEnv
    env Id
    bndr OccEnv -> WithUsageDetails r
    thing_inside
      = OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails (OccInfo, r))
    -> WithUsageDetails (OccInfo, r)
    forall a.
    OccEnv
    -> Id -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeOne OccEnv
    env Id
    bndr ((OccEnv -> WithUsageDetails (OccInfo, r))
     -> WithUsageDetails (OccInfo, r))
    -> (OccEnv -> WithUsageDetails (OccInfo, r))
    -> WithUsageDetails (OccInfo, r)
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
        let !(WUD UsageDetails
    inner_uds r
    res) = OccEnv -> WithUsageDetails r
    thing_inside OccEnv
    env
            !occ :: OccInfo
    occ = UsageDetails -> Id -> OccInfo
    lookupLetOccInfo UsageDetails
    inner_uds Id
    bndr
        in UsageDetails -> (OccInfo, r) -> WithUsageDetails (OccInfo, r)
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    inner_uds (OccInfo
    occ, r
    res)

    -----------------
    occAnalNonRecRhs :: OccEnv -> ImpRuleEdges -> JoinPointHood
                     -> Id -> CoreExpr
                     -> ([UsageDetails], Id, CoreExpr)
    occAnalNonRecRhs :: OccEnv
    -> ImpRuleEdges
    -> JoinPointHood
    -> Id
    -> CoreExpr
    -> ([UsageDetails], Id, CoreExpr)
    occAnalNonRecRhs !OccEnv
    env ImpRuleEdges
    imp_rule_edges JoinPointHood
    mb_join Id
    bndr CoreExpr
    rhs
      | [CoreRule] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [CoreRule]
    rules, [(Activation, VarSet)] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Activation, VarSet)]
    imp_rule_infos
      =  -- Fast path for common case of no rules. This is only worth
         -- 0.1% perf on average, but it's also only a line or two of code
        ( [UsageDetails
    adj_rhs_uds, UsageDetails
    adj_unf_uds],              Id
    final_bndr_no_rules,   CoreExpr
    final_rhs )
      | Bool
    otherwise
      = (UsageDetails
    adj_rhs_uds UsageDetails -> [UsageDetails] -> [UsageDetails]
    forall a. a -> [a] -> [a]
    : UsageDetails
    adj_unf_uds UsageDetails -> [UsageDetails] -> [UsageDetails]
    forall a. a -> [a] -> [a]
    : [UsageDetails]
    adj_rule_uds, Id
    final_bndr_with_rules, CoreExpr
    final_rhs )
      where
        --------- Right hand side ---------
        -- For join points, set occ_encl to OccVanilla, via setTailCtxt.  If we have
        --    join j = Just (f x) in ...
        -- we do not want to float the (f x) to
        --    let y = f x in join j = Just y in ...
        -- That's that OccRhs would do; but there's no point because
        -- j will never be scrutinised.
        rhs_env :: OccEnv
    rhs_env  = OccEnv
    -> RecFlag -> OccEncl -> JoinPointHood -> Id -> CoreExpr -> OccEnv
    mkRhsOccEnv OccEnv
    env RecFlag
    NonRecursive OccEncl
    rhs_ctxt JoinPointHood
    mb_join Id
    bndr CoreExpr
    rhs
        rhs_ctxt :: OccEncl
    rhs_ctxt = Id -> Unfolding -> OccEncl
    mkNonRecRhsCtxt Id
    bndr Unfolding
    unf

        -- See Note [Join arity prediction based on joinRhsArity]
        -- Match join arity O from mb_join_arity with manifest join arity M as
        -- returned by of occAnalLamTail. It's totally OK for them to mismatch;
        -- hence adjust the UDs from the RHS
        WUD UsageDetails
    adj_rhs_uds CoreExpr
    final_rhs = JoinPointHood
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    adjustNonRecRhs JoinPointHood
    mb_join (WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr)
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    forall a b. (a -> b) -> a -> b
    $
                                    OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    rhs_env CoreExpr
    rhs
        final_bndr_with_rules :: Id
    final_bndr_with_rules
          | OccEnv -> Bool
    noBinderSwaps OccEnv
    env = Id
    bndr -- See Note [Unfoldings and rules]
          | Bool
    otherwise         = Id
    bndr Id -> RuleInfo -> Id
    `setIdSpecialisation` [CoreRule] -> RuleInfo
    mkRuleInfo [CoreRule]
    rules'
                                     Id -> Unfolding -> Id
    `setIdUnfolding` Unfolding
    unf1
        final_bndr_no_rules :: Id
    final_bndr_no_rules
          | OccEnv -> Bool
    noBinderSwaps OccEnv
    env = Id
    bndr -- See Note [Unfoldings and rules]
          | Bool
    otherwise         = Id
    bndr Id -> Unfolding -> Id
    `setIdUnfolding` Unfolding
    unf1

        --------- Unfolding ---------
        -- See Note [Join points and unfoldings/rules]
        unf :: Unfolding
    unf = IdUnfoldingFun
    idUnfolding Id
    bndr
        WTUD TailUsageDetails
    unf_tuds Unfolding
    unf1 = OccEnv -> Unfolding -> WithTailUsageDetails Unfolding
    occAnalUnfolding OccEnv
    rhs_env Unfolding
    unf
        adj_unf_uds :: UsageDetails
    adj_unf_uds = JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity JoinPointHood
    mb_join TailUsageDetails
    unf_tuds

        --------- Rules ---------
        -- See Note [Rules are extra RHSs] and Note [Rule dependency info]
        -- and Note [Join points and unfoldings/rules]
        rules :: [CoreRule]
    rules        = Id -> [CoreRule]
    idCoreRules Id
    bndr
        rules_w_uds :: [(CoreRule, UsageDetails, TailUsageDetails)]
    rules_w_uds  = (CoreRule -> (CoreRule, UsageDetails, TailUsageDetails))
    -> [CoreRule] -> [(CoreRule, UsageDetails, TailUsageDetails)]
    forall a b. (a -> b) -> [a] -> [b]
    map (OccEnv -> CoreRule -> (CoreRule, UsageDetails, TailUsageDetails)
    occAnalRule OccEnv
    rhs_env) [CoreRule]
    rules
        rules' :: [CoreRule]
    rules'       = ((CoreRule, UsageDetails, TailUsageDetails) -> CoreRule)
    -> [(CoreRule, UsageDetails, TailUsageDetails)] -> [CoreRule]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreRule, UsageDetails, TailUsageDetails) -> CoreRule
    forall a b c. (a, b, c) -> a
    fstOf3 [(CoreRule, UsageDetails, TailUsageDetails)]
    rules_w_uds
        imp_rule_infos :: [(Activation, VarSet)]
    imp_rule_infos = ImpRuleEdges -> Id -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges Id
    bndr
        imp_rule_uds :: [UsageDetails]
    imp_rule_uds   = [[(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage [(Activation, VarSet)]
    imp_rule_infos]
             -- imp_rule_uds: consider
             --     h = ...
             --     g = ...
             --     RULE map g = h
             -- Then we want to ensure that h is in scope everywhere
             -- that g is (since the RULE might turn g into h), so
             -- we make g mention h.

        adj_rule_uds :: [UsageDetails]
        adj_rule_uds :: [UsageDetails]
    adj_rule_uds = [UsageDetails]
    imp_rule_uds [UsageDetails] -> [UsageDetails] -> [UsageDetails]
    forall a. [a] -> [a] -> [a]
    ++
                       [ UsageDetails
    l UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity JoinPointHood
    mb_join TailUsageDetails
    r
                       | (CoreRule
    _,UsageDetails
    l,TailUsageDetails
    r) <- [(CoreRule, UsageDetails, TailUsageDetails)]
    rules_w_uds ]

    mkNonRecRhsCtxt :: Id -> Unfolding -> OccEncl
    -- Precondition: Id is not a join point
    mkNonRecRhsCtxt :: Id -> Unfolding -> OccEncl
    mkNonRecRhsCtxt Id
    bndr Unfolding
    unf
      | Bool
    certainly_inline = OccEncl
    OccVanilla -- See Note [Cascading inlines]
      | Bool
    otherwise        = OccEncl
    OccRhs
      where
        certainly_inline :: Bool
    certainly_inline -- See Note [Cascading inlines]
          = -- mkNonRecRhsCtxt is only used for non-join points, so occAnalBind
            -- has set the OccInfo for this binder before calling occAnalNonRecRhs
            case Id -> OccInfo
    idOccInfo Id
    bndr of
              OneOcc { occ_in_lam :: OccInfo -> InsideLam
    occ_in_lam = InsideLam
    NotInsideLam, occ_n_br :: OccInfo -> JoinArity
    occ_n_br = JoinArity
    1 }
                -> Bool
    active Bool -> Bool -> Bool
    && Bool
    not_stable
              OccInfo
    _ -> Bool
    False

        active :: Bool
    active     = Activation -> Bool
    isAlwaysActive (Id -> Activation
    idInlineActivation Id
    bndr)
        not_stable :: Bool
    not_stable = Bool -> Bool
    not (Unfolding -> Bool
    isStableUnfolding Unfolding
    unf)

    -----------------
    occAnalRecBind :: OccEnv -> TopLevelFlag -> ImpRuleEdges -> [(Var,CoreExpr)]
                   -> UsageDetails -> WithUsageDetails [CoreBind]
    -- For a recursive group, we
    --      * occ-analyse all the RHSs
    --      * compute strongly-connected components
    --      * feed those components to occAnalRec
    -- See Note [Recursive bindings: the grand plan]
    occAnalRecBind :: OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> [(Id, CoreExpr)]
    -> UsageDetails
    -> WithUsageDetails CoreProgram
    occAnalRecBind !OccEnv
    rhs_env TopLevelFlag
    lvl ImpRuleEdges
    imp_rule_edges [(Id, CoreExpr)]
    pairs UsageDetails
    body_usage
      = (SCC NodeDetails
     -> WithUsageDetails CoreProgram -> WithUsageDetails CoreProgram)
    -> WithUsageDetails CoreProgram
    -> [SCC NodeDetails]
    -> WithUsageDetails CoreProgram
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (OccEnv
    -> TopLevelFlag
    -> SCC NodeDetails
    -> WithUsageDetails CoreProgram
    -> WithUsageDetails CoreProgram
    occAnalRec OccEnv
    rhs_env TopLevelFlag
    lvl) (UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_usage []) [SCC NodeDetails]
    sccs
      where
        sccs :: [SCC NodeDetails]
        sccs :: [SCC NodeDetails]
    sccs = [Node Unique NodeDetails] -> [SCC NodeDetails]
    forall key payload.
    Uniquable key =>
    [Node key payload] -> [SCC payload]
    stronglyConnCompFromEdgedVerticesUniq [Node Unique NodeDetails]
    nodes

        nodes :: [LetrecNode]
        nodes :: [Node Unique NodeDetails]
    nodes = ((Id, CoreExpr) -> Node Unique NodeDetails)
    -> [(Id, CoreExpr)] -> [Node Unique NodeDetails]
    forall a b. (a -> b) -> [a] -> [b]
    map (OccEnv
    -> ImpRuleEdges
    -> VarSet
    -> (Id, CoreExpr)
    -> Node Unique NodeDetails
    makeNode OccEnv
    rhs_env ImpRuleEdges
    imp_rule_edges VarSet
    bndr_set) [(Id, CoreExpr)]
    pairs

        bndrs :: [Id]
    bndrs    = ((Id, CoreExpr) -> Id) -> [(Id, CoreExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, CoreExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, CoreExpr)]
    pairs
        bndr_set :: VarSet
    bndr_set = [Id] -> VarSet
    mkVarSet [Id]
    bndrs

    -----------------------------
    occAnalRec :: OccEnv -> TopLevelFlag
               -> SCC NodeDetails
               -> WithUsageDetails [CoreBind]
               -> WithUsageDetails [CoreBind]

    -- The NonRec case is just like a Let (NonRec ...) above
    occAnalRec :: OccEnv
    -> TopLevelFlag
    -> SCC NodeDetails
    -> WithUsageDetails CoreProgram
    -> WithUsageDetails CoreProgram
    occAnalRec !OccEnv
    _ TopLevelFlag
    lvl
               (AcyclicSCC (ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    bndr, nd_rhs :: NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs = WithTailUsageDetails CoreExpr
    wtuds }))
               (WUD UsageDetails
    body_uds CoreProgram
    binds)
      | OccInfo -> Bool
    isDeadOcc OccInfo
    occ  -- Check for dead code: see Note [Dead code]
      = UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_uds CoreProgram
    binds
      | Bool
    otherwise
      = let (Id
    bndr', JoinPointHood
    mb_join) = TopLevelFlag -> OccInfo -> Id -> (Id, JoinPointHood)
    tagNonRecBinder TopLevelFlag
    lvl OccInfo
    occ Id
    bndr
            !(WUD UsageDetails
    rhs_uds' CoreExpr
    rhs') = JoinPointHood
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    adjustNonRecRhs JoinPointHood
    mb_join WithTailUsageDetails CoreExpr
    wtuds
        in UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails
    body_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    rhs_uds')
               (Id -> CoreExpr -> CoreBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    bndr' CoreExpr
    rhs' CoreBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds)
      where
        occ :: OccInfo
    occ = UsageDetails -> Id -> OccInfo
    lookupLetOccInfo UsageDetails
    body_uds Id
    bndr

    -- The Rec case is the interesting one
    -- See Note [Recursive bindings: the grand plan]
    -- See Note [Loop breaking]
    occAnalRec OccEnv
    env TopLevelFlag
    lvl (CyclicSCC [NodeDetails]
    details_s) (WUD UsageDetails
    body_uds CoreProgram
    binds)
      | Bool -> Bool
    not ((NodeDetails -> Bool) -> [NodeDetails] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any NodeDetails -> Bool
    needed [NodeDetails]
    details_s)
      = -- Check for dead code: see Note [Dead code]
        -- NB: Only look at body_uds, ignoring uses in the SCC
        UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    body_uds CoreProgram
    binds

      | Bool
    otherwise
      = UsageDetails -> CoreProgram -> WithUsageDetails CoreProgram
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    final_uds ([(Id, CoreExpr)] -> CoreBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, CoreExpr)]
    pairs CoreBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds)
      where
        all_simple :: Bool
    all_simple = (NodeDetails -> Bool) -> [NodeDetails] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all NodeDetails -> Bool
    nd_simple [NodeDetails]
    details_s

        needed :: NodeDetails -> Bool
        needed :: NodeDetails -> Bool
    needed (ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    bndr }) = Id -> Bool
    isExportedId Id
    bndr Bool -> Bool -> Bool
    || Id
    bndr Id -> VarEnv LocalOcc -> Bool
    forall a. Id -> VarEnv a -> Bool
    `elemVarEnv` VarEnv LocalOcc
    body_env
        body_env :: VarEnv LocalOcc
    body_env = UsageDetails -> VarEnv LocalOcc
    ud_env UsageDetails
    body_uds

        ------------------------------
        -- Make the nodes for the loop-breaker analysis
        -- See Note [Choosing loop breakers] for loop_breaker_nodes
        final_uds :: UsageDetails
        loop_breaker_nodes :: [LoopBreakerNode]
        WUD UsageDetails
    final_uds [LoopBreakerNode]
    loop_breaker_nodes = OccEnv
    -> TopLevelFlag
    -> UsageDetails
    -> [NodeDetails]
    -> WithUsageDetails [LoopBreakerNode]
    mkLoopBreakerNodes OccEnv
    env TopLevelFlag
    lvl UsageDetails
    body_uds [NodeDetails]
    details_s

        ------------------------------
        weak_fvs :: VarSet
        weak_fvs :: VarSet
    weak_fvs = (NodeDetails -> VarSet) -> [NodeDetails] -> VarSet
    forall a. (a -> VarSet) -> [a] -> VarSet
    mapUnionVarSet NodeDetails -> VarSet
    nd_weak_fvs [NodeDetails]
    details_s

        ---------------------------
        -- Now reconstruct the cycle
        pairs :: [(Id,CoreExpr)]
        pairs :: [(Id, CoreExpr)]
    pairs | Bool
    all_simple = JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    reOrderNodes   JoinArity
    0 VarSet
    weak_fvs [LoopBreakerNode]
    loop_breaker_nodes []
              | Bool
    otherwise  = JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    loopBreakNodes JoinArity
    0 VarSet
    weak_fvs [LoopBreakerNode]
    loop_breaker_nodes []
              -- In the common case when all are "simple" (no rules at all)
              -- the loop_breaker_nodes will include all the scope edges
              -- so a SCC computation would yield a single CyclicSCC result;
              -- and reOrderNodes deals with exactly that case.
              -- Saves a SCC analysis in a common case

    {- *********************************************************************
    *                                                                      *
                    Loop breaking
    *                                                                      *
    ********************************************************************* -}

    {- Note [Choosing loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In Step 4 in Note [Recursive bindings: the grand plan]), occAnalRec does
    loop-breaking on each CyclicSCC of the original program:

    * mkLoopBreakerNodes: Form the loop-breaker graph for that CyclicSCC

    * loopBreakNodes: Do SCC analysis on it

    * reOrderNodes: For each CyclicSCC, pick a loop breaker
        * Delete edges to that loop breaker
        * Do another SCC analysis on that reduced SCC
        * Repeat

    To form the loop-breaker graph, we construct a new set of Nodes, the
    "loop-breaker nodes", with the same details but different edges, the
    "loop-breaker edges".  The loop-breaker nodes have both more and fewer
    dependencies than the scope edges:

      More edges:
         If f calls g, and g has an active rule that mentions h then
         we add an edge from f -> h.  See Note [Rules and loop breakers].

      Fewer edges: we only include dependencies
         * only on /active/ rules,
         * on rule /RHSs/ (not LHSs)

    The scope edges, by contrast, must be much more inclusive.

    The nd_simple flag tracks the common case when a binding has no RULES
    at all, in which case the loop-breaker edges will be identical to the
    scope edges.

    Note that in Example [eftInt], *neither* eftInt *nor* eftIntFB is
    chosen as a loop breaker, because their RHSs don't mention each other.
    And indeed both can be inlined safely.

    Note [inl_fvs]
    ~~~~~~~~~~~~~~
    Note that the loop-breaker graph includes edges for occurrences in
    /both/ the RHS /and/ the stable unfolding.  Consider this, which actually
    occurred when compiling BooleanFormula.hs in GHC:

      Rec { lvl1 = go
          ; lvl2[StableUnf = go] = lvl1
          ; go = ...go...lvl2... }

    From the point of view of infinite inlining, we need only these edges:
       lvl1 :-> go
       lvl2 :-> go       -- The RHS lvl1 will never be used for inlining
       go   :-> go, lvl2

    But the danger is that, lacking any edge to lvl1, we'll put it at the
    end thus
      Rec { lvl2[ StableUnf = go] = lvl1
          ; go[LoopBreaker] = ...go...lvl2... }
          ; lvl1[Occ=Once]  = go }

    And now the Simplifer will try to use PreInlineUnconditionally on lvl1
    (which occurs just once), but because it is last we won't actually
    substitute in lvl2.  Sigh.

    To avoid this possibility, we include edges from lvl2 to /both/ its
    stable unfolding /and/ its RHS.  Hence the defn of inl_fvs in
    makeNode.  Maybe we could be more clever, but it's very much a corner
    case.

    Note [Weak loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    There is a last nasty wrinkle.  Suppose we have

        Rec { f = f_rhs
              RULE f [] = g

              h = h_rhs
              g = h
              ...more... }

    Remember that we simplify the RULES before any RHS (see Note
    [Rules are visible in their own rec group] above).

    So we must *not* postInlineUnconditionally 'g', even though
    its RHS turns out to be trivial.  (I'm assuming that 'g' is
    not chosen as a loop breaker.)  Why not?  Because then we
    drop the binding for 'g', which leaves it out of scope in the
    RULE!

    Here's a somewhat different example of the same thing
        Rec { q = r
            ; r = ...p...
            ; p = p_rhs
              RULE p [] = q }
    Here the RULE is "below" q, but we *still* can't postInlineUnconditionally
    q, because the RULE for p is active throughout.  So the RHS of r
    might rewrite to     r = ...q...
    So q must remain in scope in the output program!

    We "solve" this by:

        Make q a "weak" loop breaker (OccInfo = IAmLoopBreaker True)
        iff q is a mentioned in the RHS of any RULE (active on not)
        in the Rec group

    Note the "active or not" comment; even if a RULE is inactive, we
    want its RHS free vars to stay alive (#20820)!

    A normal "strong" loop breaker has IAmLoopBreaker False.  So:

                                    Inline  postInlineUnconditionally
    strong   IAmLoopBreaker False    no      no
    weak     IAmLoopBreaker True     yes     no
             other                   yes     yes

    The **sole** reason for this kind of loop breaker is so that
    postInlineUnconditionally does not fire.  Ugh.

    Annoyingly, since we simplify the rules *first* we'll never inline
    q into p's RULE.  That trivial binding for q will hang around until
    we discard the rule.  Yuk.  But it's rare.

    Note [Rules and loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we form the loop-breaker graph (Step 4 in Note [Recursive
    bindings: the grand plan]), we must be careful about RULEs.

    For a start, we want a loop breaker to cut every cycle, so inactive
    rules play no part; we need only consider /active/ rules.
    See Note [Finding rule RHS free vars]

    The second point is more subtle.  A RULE is like an equation for
    'f' that is *always* inlined if it is applicable.  We do *not* disable
    rules for loop-breakers.  It's up to whoever makes the rules to make
    sure that the rules themselves always terminate.  See Note [Rules for
    recursive functions] in GHC.Core.Opt.Simplify

    Hence, if
        f's RHS (or its stable unfolding if it has one) mentions g, and
        g has a RULE that mentions h, and
        h has a RULE that mentions f

    then we *must* choose f to be a loop breaker.  Example: see Note
    [Specialisation rules]. So our plan is this:

       Take the free variables of f's RHS, and augment it with all the
       variables reachable by a transitive sequence RULES from those
       starting points.

    That is the whole reason for computing rule_fv_env in mkLoopBreakerNodes.
    Wrinkles:

    * We only consider /active/ rules. See Note [Finding rule RHS free vars]

    * We need only consider free vars that are also binders in this Rec
      group.  See also Note [Finding rule RHS free vars]

    * We only consider variables free in the *RHS* of the rule, in
      contrast to the way we build the Rec group in the first place (Note
      [Rule dependency info])

    * Why "transitive sequence of rules"?  Because active rules apply
      unconditionally, without checking loop-breaker-ness.
     See Note [Loop breaker dependencies].

    Note [Finding rule RHS free vars]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this real example from Data Parallel Haskell
         tagZero :: Array Int -> Array Tag
         {-# INLINE [1] tagZeroes #-}
         tagZero xs = pmap (\x -> fromBool (x==0)) xs

         {-# RULES "tagZero" [~1] forall xs n.
             pmap fromBool <blah blah> = tagZero xs #-}
    So tagZero's RHS mentions pmap, and pmap's RULE mentions tagZero.
    However, tagZero can only be inlined in phase 1 and later, while
    the RULE is only active *before* phase 1.  So there's no problem.

    To make this work, we look for the RHS free vars only for
    *active* rules. That's the reason for the occ_rule_act field
    of the OccEnv.

    Note [loopBreakNodes]
    ~~~~~~~~~~~~~~~~~~~~~
    loopBreakNodes is applied to the list of nodes for a cyclic strongly
    connected component (there's guaranteed to be a cycle).  It returns
    the same nodes, but
            a) in a better order,
            b) with some of the Ids having a IAmALoopBreaker pragma

    The "loop-breaker" Ids are sufficient to break all cycles in the SCC.  This means
    that the simplifier can guarantee not to loop provided it never records an inlining
    for these no-inline guys.

    Furthermore, the order of the binds is such that if we neglect dependencies
    on the no-inline Ids then the binds are topologically sorted.  This means
    that the simplifier will generally do a good job if it works from top bottom,
    recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
    -}

    type Binding = (Id,CoreExpr)

    -- See Note [loopBreakNodes]
    loopBreakNodes :: Int
                   -> VarSet        -- Binders whose dependencies may be "missing"
                                    -- See Note [Weak loop breakers]
                   -> [LoopBreakerNode]
                   -> [Binding]             -- Append these to the end
                   -> [Binding]

    -- Return the bindings sorted into a plausible order, and marked with loop breakers.
    -- See Note [loopBreakNodes]
    loopBreakNodes :: JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    loopBreakNodes JoinArity
    depth VarSet
    weak_fvs [LoopBreakerNode]
    nodes [(Id, CoreExpr)]
    binds
      = -- pprTrace "loopBreakNodes" (ppr nodes) $
        [SCC LoopBreakerNode] -> [(Id, CoreExpr)]
    go ([LoopBreakerNode] -> [SCC LoopBreakerNode]
    forall key payload.
    Uniquable key =>
    [Node key payload] -> [SCC (Node key payload)]
    stronglyConnCompFromEdgedVerticesUniqR [LoopBreakerNode]
    nodes)
      where
        go :: [SCC LoopBreakerNode] -> [(Id, CoreExpr)]
    go []         = [(Id, CoreExpr)]
    binds
        go (SCC LoopBreakerNode
    scc:[SCC LoopBreakerNode]
    sccs) = SCC LoopBreakerNode -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    loop_break_scc SCC LoopBreakerNode
    scc ([SCC LoopBreakerNode] -> [(Id, CoreExpr)]
    go [SCC LoopBreakerNode]
    sccs)

        loop_break_scc :: SCC LoopBreakerNode -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    loop_break_scc SCC LoopBreakerNode
    scc [(Id, CoreExpr)]
    binds
          = case SCC LoopBreakerNode
    scc of
              AcyclicSCC LoopBreakerNode
    node  -> (Id -> Id) -> LoopBreakerNode -> (Id, CoreExpr)
    nodeBinding (VarSet -> Id -> Id
    mk_non_loop_breaker VarSet
    weak_fvs) LoopBreakerNode
    node (Id, CoreExpr) -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(Id, CoreExpr)]
    binds
              CyclicSCC [LoopBreakerNode]
    nodes  -> JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    reOrderNodes JoinArity
    depth VarSet
    weak_fvs [LoopBreakerNode]
    nodes [(Id, CoreExpr)]
    binds

    ----------------------------------
    reOrderNodes :: Int -> VarSet -> [LoopBreakerNode] -> [Binding] -> [Binding]
        -- Choose a loop breaker, mark it no-inline,
        -- and call loopBreakNodes on the rest
    reOrderNodes :: JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    reOrderNodes JoinArity
    _ VarSet
    _ []     [(Id, CoreExpr)]
    _     = String -> [(Id, CoreExpr)]
    forall a. HasCallStack => String -> a
    panic String
    "reOrderNodes"
    reOrderNodes JoinArity
    _ VarSet
    _ [LoopBreakerNode
    node] [(Id, CoreExpr)]
    binds = (Id -> Id) -> LoopBreakerNode -> (Id, CoreExpr)
    nodeBinding Id -> Id
    mk_loop_breaker LoopBreakerNode
    node (Id, CoreExpr) -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. a -> [a] -> [a]
    : [(Id, CoreExpr)]
    binds
    reOrderNodes JoinArity
    depth VarSet
    weak_fvs (LoopBreakerNode
    node : [LoopBreakerNode]
    nodes) [(Id, CoreExpr)]
    binds
      = -- pprTrace "reOrderNodes" (vcat [ text "unchosen" <+> ppr unchosen
        --                               , text "chosen" <+> ppr chosen_nodes ]) $
        JoinArity
    -> VarSet
    -> [LoopBreakerNode]
    -> [(Id, CoreExpr)]
    -> [(Id, CoreExpr)]
    loopBreakNodes JoinArity
    new_depth VarSet
    weak_fvs [LoopBreakerNode]
    unchosen ([(Id, CoreExpr)] -> [(Id, CoreExpr)])
    -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a b. (a -> b) -> a -> b
    $
        ((LoopBreakerNode -> (Id, CoreExpr))
    -> [LoopBreakerNode] -> [(Id, CoreExpr)]
    forall a b. (a -> b) -> [a] -> [b]
    map ((Id -> Id) -> LoopBreakerNode -> (Id, CoreExpr)
    nodeBinding Id -> Id
    mk_loop_breaker) [LoopBreakerNode]
    chosen_nodes [(Id, CoreExpr)] -> [(Id, CoreExpr)] -> [(Id, CoreExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id, CoreExpr)]
    binds)
      where
        ([LoopBreakerNode]
    chosen_nodes, [LoopBreakerNode]
    unchosen) = Bool
    -> NodeScore
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> ([LoopBreakerNode], [LoopBreakerNode])
    chooseLoopBreaker Bool
    approximate_lb
                                                     (SimpleNodeDetails -> NodeScore
    snd_score (LoopBreakerNode -> SimpleNodeDetails
    forall key payload. Node key payload -> payload
    node_payload LoopBreakerNode
    node))
                                                     [LoopBreakerNode
    node] [] [LoopBreakerNode]
    nodes

        approximate_lb :: Bool
    approximate_lb = JoinArity
    depth JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    2
        new_depth :: JoinArity
    new_depth | Bool
    approximate_lb = JoinArity
    0
                  | Bool
    otherwise      = JoinArity
    depthJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
            -- After two iterations (d=0, d=1) give up
            -- and approximate, returning to d=0

    nodeBinding :: (Id -> Id) -> LoopBreakerNode -> Binding
    nodeBinding :: (Id -> Id) -> LoopBreakerNode -> (Id, CoreExpr)
    nodeBinding Id -> Id
    set_id_occ (LoopBreakerNode -> SimpleNodeDetails
    forall key payload. Node key payload -> payload
    node_payload -> SND { snd_bndr :: SimpleNodeDetails -> Id
    snd_bndr = Id
    bndr, snd_rhs :: SimpleNodeDetails -> CoreExpr
    snd_rhs = CoreExpr
    rhs})
      = (Id -> Id
    set_id_occ Id
    bndr, CoreExpr
    rhs)

    mk_loop_breaker :: Id -> Id
    mk_loop_breaker :: Id -> Id
    mk_loop_breaker Id
    bndr
      = Id
    bndr Id -> OccInfo -> Id
    `setIdOccInfo` OccInfo
    occ'
      where
        occ' :: OccInfo
    occ'      = OccInfo
    strongLoopBreaker { occ_tail = tail_info }
        tail_info :: TailCallInfo
    tail_info = OccInfo -> TailCallInfo
    tailCallInfo (Id -> OccInfo
    idOccInfo Id
    bndr)

    mk_non_loop_breaker :: VarSet -> Id -> Id
    -- See Note [Weak loop breakers]
    mk_non_loop_breaker :: VarSet -> Id -> Id
    mk_non_loop_breaker VarSet
    weak_fvs Id
    bndr
      | Id
    bndr Id -> VarSet -> Bool
    `elemVarSet` VarSet
    weak_fvs = Id -> OccInfo -> Id
    setIdOccInfo Id
    bndr OccInfo
    occ'
      | Bool
    otherwise                  = Id
    bndr
      where
        occ' :: OccInfo
    occ'      = OccInfo
    weakLoopBreaker { occ_tail = tail_info }
        tail_info :: TailCallInfo
    tail_info = OccInfo -> TailCallInfo
    tailCallInfo (Id -> OccInfo
    idOccInfo Id
    bndr)

    ----------------------------------
    chooseLoopBreaker :: Bool                -- True <=> Too many iterations,
                                             --          so approximate
                      -> NodeScore           -- Best score so far
                      -> [LoopBreakerNode]   -- Nodes with this score
                      -> [LoopBreakerNode]   -- Nodes with higher scores
                      -> [LoopBreakerNode]   -- Unprocessed nodes
                      -> ([LoopBreakerNode], [LoopBreakerNode])
        -- This loop looks for the bind with the lowest score
        -- to pick as the loop  breaker.  The rest accumulate in
    chooseLoopBreaker :: Bool
    -> NodeScore
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> ([LoopBreakerNode], [LoopBreakerNode])
    chooseLoopBreaker Bool
    _ NodeScore
    _ [LoopBreakerNode]
    loop_nodes [LoopBreakerNode]
    acc []
      = ([LoopBreakerNode]
    loop_nodes, [LoopBreakerNode]
    acc)        -- Done

        -- If approximate_loop_breaker is True, we pick *all*
        -- nodes with lowest score, else just one
        -- See Note [Complexity of loop breaking]
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc [LoopBreakerNode]
    loop_nodes [LoopBreakerNode]
    acc (LoopBreakerNode
    node : [LoopBreakerNode]
    nodes)
      | Bool
    approx_lb
      , NodeScore -> JoinArity
    rank NodeScore
    sc JoinArity -> JoinArity -> Bool
    forall a. Eq a => a -> a -> Bool
    == NodeScore -> JoinArity
    rank NodeScore
    loop_sc
      = Bool
    -> NodeScore
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> ([LoopBreakerNode], [LoopBreakerNode])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc (LoopBreakerNode
    node LoopBreakerNode -> [LoopBreakerNode] -> [LoopBreakerNode]
    forall a. a -> [a] -> [a]
    : [LoopBreakerNode]
    loop_nodes) [LoopBreakerNode]
    acc [LoopBreakerNode]
    nodes

      | NodeScore
    sc NodeScore -> NodeScore -> Bool
    `betterLB` NodeScore
    loop_sc  -- Better score so pick this new one
      = Bool
    -> NodeScore
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> ([LoopBreakerNode], [LoopBreakerNode])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    sc [LoopBreakerNode
    node] ([LoopBreakerNode]
    loop_nodes [LoopBreakerNode] -> [LoopBreakerNode] -> [LoopBreakerNode]
    forall a. [a] -> [a] -> [a]
    ++ [LoopBreakerNode]
    acc) [LoopBreakerNode]
    nodes

      | Bool
    otherwise              -- Worse score so don't pick it
      = Bool
    -> NodeScore
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> [LoopBreakerNode]
    -> ([LoopBreakerNode], [LoopBreakerNode])
    chooseLoopBreaker Bool
    approx_lb NodeScore
    loop_sc [LoopBreakerNode]
    loop_nodes (LoopBreakerNode
    node LoopBreakerNode -> [LoopBreakerNode] -> [LoopBreakerNode]
    forall a. a -> [a] -> [a]
    : [LoopBreakerNode]
    acc) [LoopBreakerNode]
    nodes
      where
        sc :: NodeScore
    sc = SimpleNodeDetails -> NodeScore
    snd_score (LoopBreakerNode -> SimpleNodeDetails
    forall key payload. Node key payload -> payload
    node_payload LoopBreakerNode
    node)

    {-
    Note [Complexity of loop breaking]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The loop-breaking algorithm knocks out one binder at a time, and
    performs a new SCC analysis on the remaining binders.  That can
    behave very badly in tightly-coupled groups of bindings; in the
    worst case it can be (N**2)*log N, because it does a full SCC
    on N, then N-1, then N-2 and so on.

    To avoid this, we switch plans after 2 (or whatever) attempts:
      Plan A: pick one binder with the lowest score, make it
              a loop breaker, and try again
      Plan B: pick *all* binders with the lowest score, make them
              all loop breakers, and try again
    Since there are only a small finite number of scores, this will
    terminate in a constant number of iterations, rather than O(N)
    iterations.

    You might thing that it's very unlikely, but RULES make it much
    more likely.  Here's a real example from #1969:
      Rec { $dm = \d.\x. op d
            {-# RULES forall d. $dm Int d  = $s$dm1
                      forall d. $dm Bool d = $s$dm2 #-}

            dInt = MkD .... opInt ...
            dInt = MkD .... opBool ...
            opInt  = $dm dInt
            opBool = $dm dBool

            $s$dm1 = \x. op dInt
            $s$dm2 = \x. op dBool }
    The RULES stuff means that we can't choose $dm as a loop breaker
    (Note [Choosing loop breakers]), so we must choose at least (say)
    opInt *and* opBool, and so on.  The number of loop breakers is
    linear in the number of instance declarations.

    Note [Loop breakers and INLINE/INLINABLE pragmas]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Avoid choosing a function with an INLINE pramga as the loop breaker!
    If such a function is mutually-recursive with a non-INLINE thing,
    then the latter should be the loop-breaker.

    It's vital to distinguish between INLINE and INLINABLE (the
    Bool returned by hasStableCoreUnfolding_maybe).  If we start with
       Rec { {-# INLINABLE f #-}
             f x = ...f... }
    and then worker/wrapper it through strictness analysis, we'll get
       Rec { {-# INLINABLE $wf #-}
             $wf p q = let x = (p,q) in ...f...

             {-# INLINE f #-}
             f x = case x of (p,q) -> $wf p q }

    Now it is vital that we choose $wf as the loop breaker, so we can
    inline 'f' in '$wf'.

    Note [DFuns should not be loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's particularly bad to make a DFun into a loop breaker.  See
    Note [How instance declarations are translated] in GHC.Tc.TyCl.Instance

    We give DFuns a higher score than ordinary CONLIKE things because
    if there's a choice we want the DFun to be the non-loop breaker. Eg

    rec { sc = /\ a \$dC. $fBWrap (T a) ($fCT @ a $dC)

          $fCT :: forall a_afE. (Roman.C a_afE) => Roman.C (Roman.T a_afE)
          {-# DFUN #-}
          $fCT = /\a \$dC. MkD (T a) ((sc @ a $dC) |> blah) ($ctoF @ a $dC)
        }

    Here 'sc' (the superclass) looks CONLIKE, but we'll never get to it
    if we can't unravel the DFun first.

    Note [Constructor applications]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    It's really really important to inline dictionaries.  Real
    example (the Enum Ordering instance from GHC.Base):

         rec     f = \ x -> case d of (p,q,r) -> p x
                 g = \ x -> case d of (p,q,r) -> q x
                 d = (v, f, g)

    Here, f and g occur just once; but we can't inline them into d.
    On the other hand we *could* simplify those case expressions if
    we didn't stupidly choose d as the loop breaker.
    But we won't because constructor args are marked "Many".
    Inlining dictionaries is really essential to unravelling
    the loops in static numeric dictionaries, see GHC.Float.

    Note [Closure conversion]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    We treat (\x. C p q) as a high-score candidate in the letrec scoring algorithm.
    The immediate motivation came from the result of a closure-conversion transformation
    which generated code like this:

        data Clo a b = forall c. Clo (c -> a -> b) c

        ($:) :: Clo a b -> a -> b
        Clo f env $: x = f env x

        rec { plus = Clo plus1 ()

            ; plus1 _ n = Clo plus2 n

            ; plus2 Zero     n = n
            ; plus2 (Succ m) n = Succ (plus $: m $: n) }

    If we inline 'plus' and 'plus1', everything unravels nicely.  But if
    we choose 'plus1' as the loop breaker (which is entirely possible
    otherwise), the loop does not unravel nicely.

    @occAnalUnfolding@ deals with the question of bindings where the Id is marked
    by an INLINE pragma.  For these we record that anything which occurs
    in its RHS occurs many times.  This pessimistically assumes that this
    inlined binder also occurs many times in its scope, but if it doesn't
    we'll catch it next time round.  At worst this costs an extra simplifier pass.
    ToDo: try using the occurrence info for the inline'd binder.

    [March 97] We do the same for atomic RHSs.  Reason: see notes with loopBreakSCC.
    [June 98, SLPJ]  I've undone this change; I don't understand it.  See notes with loopBreakSCC.

    ************************************************************************
    *                                                                      *
                       Making nodes
    *                                                                      *
    ************************************************************************
    -}

    -- | Digraph node as constructed by 'makeNode' and consumed by 'occAnalRec'.
    -- The Unique key is gotten from the Id.
    type LetrecNode = Node Unique NodeDetails

    -- | Node details as consumed by 'occAnalRec'.
    data NodeDetails
      = ND { NodeDetails -> Id
    nd_bndr :: Id          -- Binder

           , NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs  :: !(WithTailUsageDetails CoreExpr)
             -- ^ RHS, already occ-analysed
             -- With TailUsageDetails from RHS, and RULES, and stable unfoldings,
             -- ignoring phase (ie assuming all are active).
             -- NB: Unadjusted TailUsageDetails, as if this Node becomes a
             -- non-recursive join point!
             -- See Note [TailUsageDetails when forming Rec groups]

           , NodeDetails -> VarSet
    nd_inl  :: IdSet       -- Free variables of the stable unfolding and the RHS
                                    -- but excluding any RULES
                                    -- This is the IdSet that may be used if the Id is inlined

           , NodeDetails -> Bool
    nd_simple :: Bool      -- True iff this binding has no local RULES
                                    -- If all nodes are simple we don't need a loop-breaker
                                    -- dep-anal before reconstructing.

           , NodeDetails -> VarSet
    nd_weak_fvs :: IdSet    -- Variables bound in this Rec group that are free
                                     -- in the RHS of any rule (active or not) for this bndr
                                     -- See Note [Weak loop breakers]

           , NodeDetails -> VarSet
    nd_active_rule_fvs :: IdSet    -- Variables bound in this Rec group that are free
                                            -- in the RHS of an active rule for this bndr
                                            -- See Note [Rules and loop breakers]
      }

    instance Outputable NodeDetails where
       ppr :: NodeDetails -> SDoc
    ppr NodeDetails
    nd = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ND" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces
                 ([SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    sep [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "bndr =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (NodeDetails -> Id
    nd_bndr NodeDetails
    nd)
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "uds =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> TailUsageDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TailUsageDetails
    uds
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "inl =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (NodeDetails -> VarSet
    nd_inl NodeDetails
    nd)
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "simple =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Bool -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (NodeDetails -> Bool
    nd_simple NodeDetails
    nd)
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "active_rule_fvs =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (NodeDetails -> VarSet
    nd_active_rule_fvs NodeDetails
    nd)
                 ])
                where
                   WTUD TailUsageDetails
    uds CoreExpr
    _ = NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs NodeDetails
    nd

    -- | Digraph with simplified and completely occurrence analysed
    -- 'SimpleNodeDetails', retaining just the info we need for breaking loops.
    type LoopBreakerNode = Node Unique SimpleNodeDetails

    -- | Condensed variant of 'NodeDetails' needed during loop breaking.
    data SimpleNodeDetails
      = SND { SimpleNodeDetails -> Id
    snd_bndr  :: IdWithOccInfo  -- OccInfo accurate
            , SimpleNodeDetails -> CoreExpr
    snd_rhs   :: CoreExpr       -- properly occur-analysed
            , SimpleNodeDetails -> NodeScore
    snd_score :: NodeScore
            }

    instance Outputable SimpleNodeDetails where
       ppr :: SimpleNodeDetails -> SDoc
    ppr SimpleNodeDetails
    nd = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SND" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces
                 ([SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    sep [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "bndr =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (SimpleNodeDetails -> Id
    snd_bndr SimpleNodeDetails
    nd)
                      , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "score =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> NodeScore -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (SimpleNodeDetails -> NodeScore
    snd_score SimpleNodeDetails
    nd)
                 ])

    -- The NodeScore is compared lexicographically;
    --      e.g. lower rank wins regardless of size
    type NodeScore = ( Int     -- Rank: lower => more likely to be picked as loop breaker
                     , Int     -- Size of rhs: higher => more likely to be picked as LB
                               -- Maxes out at maxExprSize; we just use it to prioritise
                               -- small functions
                     , Bool )  -- Was it a loop breaker before?
                               -- True => more likely to be picked
                               -- Note [Loop breakers, node scoring, and stability]

    rank :: NodeScore -> Int
    rank :: NodeScore -> JoinArity
    rank (JoinArity
    r, JoinArity
    _, Bool
    _) = JoinArity
    r

    makeNode :: OccEnv -> ImpRuleEdges -> VarSet
             -> (Var, CoreExpr) -> LetrecNode
    -- See Note [Recursive bindings: the grand plan]
    makeNode :: OccEnv
    -> ImpRuleEdges
    -> VarSet
    -> (Id, CoreExpr)
    -> Node Unique NodeDetails
    makeNode !OccEnv
    env ImpRuleEdges
    imp_rule_edges VarSet
    bndr_set (Id
    bndr, CoreExpr
    rhs)
      = -- pprTrace "makeNode" (ppr bndr <+> ppr (sizeVarSet bndr_set)) $
        DigraphNode { node_payload :: NodeDetails
    node_payload      = NodeDetails
    details
                    , node_key :: Unique
    node_key          = Id -> Unique
    varUnique Id
    bndr
                    , node_dependencies :: [Unique]
    node_dependencies = VarSet -> [Unique]
    forall elt. UniqSet elt -> [Unique]
    nonDetKeysUniqSet VarSet
    scope_fvs }
        -- It's OK to use nonDetKeysUniqSet here as stronglyConnCompFromEdgedVerticesR
        -- is still deterministic with edges in nondeterministic order as
        -- explained in Note [Deterministic SCC] in GHC.Data.Graph.Directed.
      where
        details :: NodeDetails
    details = ND { nd_bndr :: Id
    nd_bndr            = Id
    bndr'
                     , nd_rhs :: WithTailUsageDetails CoreExpr
    nd_rhs             = TailUsageDetails -> CoreExpr -> WithTailUsageDetails CoreExpr
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    rhs_ja UsageDetails
    unadj_scope_uds) CoreExpr
    rhs'
                     , nd_inl :: VarSet
    nd_inl             = VarSet
    inl_fvs
                     , nd_simple :: Bool
    nd_simple          = [(CoreRule, UsageDetails, UsageDetails)] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds Bool -> Bool -> Bool
    && [(Activation, VarSet)] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Activation, VarSet)]
    imp_rule_info
                     , nd_weak_fvs :: VarSet
    nd_weak_fvs        = VarSet
    weak_fvs
                     , nd_active_rule_fvs :: VarSet
    nd_active_rule_fvs = VarSet
    active_rule_fvs }

        bndr' :: Id
    bndr' | OccEnv -> Bool
    noBinderSwaps OccEnv
    env = Id
    bndr  -- See Note [Unfoldings and rules]
              | Bool
    otherwise         = Id
    bndr Id -> Unfolding -> Id
    `setIdUnfolding`      Unfolding
    unf'
                                         Id -> RuleInfo -> Id
    `setIdSpecialisation` [CoreRule] -> RuleInfo
    mkRuleInfo [CoreRule]
    rules'

        -- NB: Both adj_unf_uds and adj_rule_uds have been adjusted to match the
        --     JoinArity rhs_ja of unadj_rhs_uds.
        unadj_inl_uds :: UsageDetails
    unadj_inl_uds   = UsageDetails
    unadj_rhs_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    adj_unf_uds
        unadj_scope_uds :: UsageDetails
    unadj_scope_uds = UsageDetails
    unadj_inl_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    adj_rule_uds
                       -- Note [Rules are extra RHSs]
                       -- Note [Rule dependency info]
        scope_fvs :: VarSet
    scope_fvs = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    unadj_scope_uds
        -- scope_fvs: all occurrences from this binder: RHS, unfolding,
        --            and RULES, both LHS and RHS thereof, active or inactive

        inl_fvs :: VarSet
    inl_fvs  = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    unadj_inl_uds
        -- inl_fvs: vars that would become free if the function was inlined.
        -- We conservatively approximate that by the free vars from the RHS
        -- and the unfolding together.
        -- See Note [inl_fvs]

        --------- Right hand side ---------
        -- Constructing the edges for the main Rec computation
        -- See Note [Forming Rec groups]
        -- and Note [TailUsageDetails when forming Rec groups]
        -- Compared to occAnalNonRecBind, we can't yet adjust the RHS because
        --   (a) we don't yet know the final joinpointhood. It might not become a
        --       join point after all!
        --   (b) we don't even know whether it stays a recursive RHS after the SCC
        --       analysis we are about to seed! So we can't markAllInsideLam in
        --       advance, because if it ends up as a non-recursive join point we'll
        --       consider it as one-shot and don't need to markAllInsideLam.
        -- Instead, do the occAnalLamTail call here and postpone adjustTailUsage
        -- until occAnalRec. In effect, we pretend that the RHS becomes a
        -- non-recursive join point and fix up later with adjustTailUsage.
        rhs_env :: OccEnv
    rhs_env = OccEnv
    -> RecFlag -> OccEncl -> JoinPointHood -> Id -> CoreExpr -> OccEnv
    mkRhsOccEnv OccEnv
    env RecFlag
    Recursive OccEncl
    OccRhs (Id -> JoinPointHood
    idJoinPointHood Id
    bndr) Id
    bndr CoreExpr
    rhs
                -- If bndr isn't an /existing/ join point (so idJoinPointHood = NotJoinPoint),
                -- it's safe to zap the occ_join_points, because they can't occur in RHS.
        WTUD (TUD JoinArity
    rhs_ja UsageDetails
    unadj_rhs_uds) CoreExpr
    rhs' = OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    rhs_env CoreExpr
    rhs
          -- The corresponding call to adjustTailUsage is in occAnalRec and tagRecBinders

        --------- Unfolding ---------
        -- See Note [Join points and unfoldings/rules]
        unf :: Unfolding
    unf = IdUnfoldingFun
    realIdUnfolding Id
    bndr -- realIdUnfolding: Ignore loop-breaker-ness
                                   -- here because that is what we are setting!
        WTUD TailUsageDetails
    unf_tuds Unfolding
    unf' = OccEnv -> Unfolding -> WithTailUsageDetails Unfolding
    occAnalUnfolding OccEnv
    rhs_env Unfolding
    unf
        adj_unf_uds :: UsageDetails
    adj_unf_uds = JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity (JoinArity -> JoinPointHood
    JoinPoint JoinArity
    rhs_ja) TailUsageDetails
    unf_tuds
          -- `rhs_ja` is `joinRhsArity rhs` and is the prediction for source M
          -- of Note [Join arity prediction based on joinRhsArity]

        --------- IMP-RULES --------
        is_active :: Activation -> Bool
    is_active     = OccEnv -> Activation -> Bool
    occ_rule_act OccEnv
    env :: Activation -> Bool
        imp_rule_info :: [(Activation, VarSet)]
    imp_rule_info = ImpRuleEdges -> Id -> [(Activation, VarSet)]
    lookupImpRules ImpRuleEdges
    imp_rule_edges Id
    bndr
        imp_rule_uds :: UsageDetails
    imp_rule_uds  = [(Activation, VarSet)] -> UsageDetails
    impRulesScopeUsage [(Activation, VarSet)]
    imp_rule_info
        imp_rule_fvs :: VarSet
    imp_rule_fvs  = (Activation -> Bool) -> VarSet -> [(Activation, VarSet)] -> VarSet
    impRulesActiveFvs Activation -> Bool
    is_active VarSet
    bndr_set [(Activation, VarSet)]
    imp_rule_info

        --------- All rules --------
        -- See Note [Join points and unfoldings/rules]
        -- `rhs_ja` is `joinRhsArity rhs'` and is the prediction for source M
        -- of Note [Join arity prediction based on joinRhsArity]
        rules_w_uds :: [(CoreRule, UsageDetails, UsageDetails)]
        rules_w_uds :: [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds = [ (CoreRule
    r,UsageDetails
    l,JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity (JoinArity -> JoinPointHood
    JoinPoint JoinArity
    rhs_ja) TailUsageDetails
    rhs_wuds)
                      | CoreRule
    rule <- Id -> [CoreRule]
    idCoreRules Id
    bndr
                      , let (CoreRule
    r,UsageDetails
    l,TailUsageDetails
    rhs_wuds) = OccEnv -> CoreRule -> (CoreRule, UsageDetails, TailUsageDetails)
    occAnalRule OccEnv
    rhs_env CoreRule
    rule ]
        rules' :: [CoreRule]
    rules'      = ((CoreRule, UsageDetails, UsageDetails) -> CoreRule)
    -> [(CoreRule, UsageDetails, UsageDetails)] -> [CoreRule]
    forall a b. (a -> b) -> [a] -> [b]
    map (CoreRule, UsageDetails, UsageDetails) -> CoreRule
    forall a b c. (a, b, c) -> a
    fstOf3 [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds

        adj_rule_uds :: UsageDetails
    adj_rule_uds = ((CoreRule, UsageDetails, UsageDetails)
     -> UsageDetails -> UsageDetails)
    -> UsageDetails
    -> [(CoreRule, UsageDetails, UsageDetails)]
    -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails)
    -> UsageDetails -> UsageDetails
    forall {a}.
    (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds UsageDetails
    imp_rule_uds [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_rule_uds :: (a, UsageDetails, UsageDetails) -> UsageDetails -> UsageDetails
    add_rule_uds (a
    _, UsageDetails
    l, UsageDetails
    r) UsageDetails
    uds = UsageDetails
    l UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    r UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds

        -------- active_rule_fvs ------------
        active_rule_fvs :: VarSet
    active_rule_fvs = ((CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet)
    -> VarSet -> [(CoreRule, UsageDetails, UsageDetails)] -> VarSet
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_active_rule VarSet
    imp_rule_fvs [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_active_rule :: (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_active_rule (CoreRule
    rule, UsageDetails
    _, UsageDetails
    rhs_uds) VarSet
    fvs
          | Activation -> Bool
    is_active (CoreRule -> Activation
    ruleActivation CoreRule
    rule)
          = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    rhs_uds VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    fvs
          | Bool
    otherwise
          = VarSet
    fvs

        -------- weak_fvs ------------
        -- See Note [Weak loop breakers]
        weak_fvs :: VarSet
    weak_fvs = ((CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet)
    -> VarSet -> [(CoreRule, UsageDetails, UsageDetails)] -> VarSet
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_rule VarSet
    emptyVarSet [(CoreRule, UsageDetails, UsageDetails)]
    rules_w_uds
        add_rule :: (CoreRule, UsageDetails, UsageDetails) -> VarSet -> VarSet
    add_rule (CoreRule
    _, UsageDetails
    _, UsageDetails
    rhs_uds) VarSet
    fvs = VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndr_set UsageDetails
    rhs_uds VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    fvs

    mkLoopBreakerNodes :: OccEnv -> TopLevelFlag
                       -> UsageDetails   -- for BODY of let
                       -> [NodeDetails]
                       -> WithUsageDetails [LoopBreakerNode] -- with OccInfo up-to-date
    -- See Note [Choosing loop breakers]
    -- This function primarily creates the Nodes for the
    -- loop-breaker SCC analysis.  More specifically:
    --   a) tag each binder with its occurrence info
    --   b) add a NodeScore to each node
    --   c) make a Node with the right dependency edges for
    --      the loop-breaker SCC analysis
    --   d) adjust each RHS's usage details according to
    --      the binder's (new) shotness and join-point-hood
    mkLoopBreakerNodes :: OccEnv
    -> TopLevelFlag
    -> UsageDetails
    -> [NodeDetails]
    -> WithUsageDetails [LoopBreakerNode]
    mkLoopBreakerNodes !OccEnv
    env TopLevelFlag
    lvl UsageDetails
    body_uds [NodeDetails]
    details_s
      = UsageDetails
    -> [LoopBreakerNode] -> WithUsageDetails [LoopBreakerNode]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    final_uds (String
    -> (NodeDetails -> Id -> LoopBreakerNode)
    -> [NodeDetails]
    -> [Id]
    -> [LoopBreakerNode]
    forall a b c.
    HasDebugCallStack =>
    String -> (a -> b -> c) -> [a] -> [b] -> [c]
    zipWithEqual String
    "mkLoopBreakerNodes" NodeDetails -> Id -> LoopBreakerNode
    mk_lb_node [NodeDetails]
    details_s [Id]
    bndrs')
      where
        WUD UsageDetails
    final_uds [Id]
    bndrs' = TopLevelFlag
    -> UsageDetails -> [NodeDetails] -> WithUsageDetails [Id]
    tagRecBinders TopLevelFlag
    lvl UsageDetails
    body_uds [NodeDetails]
    details_s

        mk_lb_node :: NodeDetails -> Id -> LoopBreakerNode
    mk_lb_node nd :: NodeDetails
    nd@(ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    old_bndr, nd_inl :: NodeDetails -> VarSet
    nd_inl = VarSet
    inl_fvs
                          , nd_rhs :: NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs = WTUD TailUsageDetails
    _ CoreExpr
    rhs }) Id
    new_bndr
          = DigraphNode { node_payload :: SimpleNodeDetails
    node_payload      = SimpleNodeDetails
    simple_nd
                        , node_key :: Unique
    node_key          = Id -> Unique
    varUnique Id
    old_bndr
                        , node_dependencies :: [Unique]
    node_dependencies = VarSet -> [Unique]
    forall elt. UniqSet elt -> [Unique]
    nonDetKeysUniqSet VarSet
    lb_deps }
                  -- It's OK to use nonDetKeysUniqSet here as
                  -- stronglyConnCompFromEdgedVerticesR is still deterministic with edges
                  -- in nondeterministic order as explained in
                  -- Note [Deterministic SCC] in GHC.Data.Graph.Directed.
          where
            simple_nd :: SimpleNodeDetails
    simple_nd = SND { snd_bndr :: Id
    snd_bndr = Id
    new_bndr, snd_rhs :: CoreExpr
    snd_rhs = CoreExpr
    rhs, snd_score :: NodeScore
    snd_score = NodeScore
    score }
            score :: NodeScore
    score  = OccEnv -> Id -> VarSet -> NodeDetails -> NodeScore
    nodeScore OccEnv
    env Id
    new_bndr VarSet
    lb_deps NodeDetails
    nd
            lb_deps :: VarSet
    lb_deps = VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ VarEnv VarSet
    rule_fv_env VarSet
    inl_fvs
            -- See Note [Loop breaker dependencies]

        rule_fv_env :: IdEnv IdSet
        -- Maps a variable f to the variables from this group
        --      reachable by a sequence of RULES starting with f
        -- Domain is *subset* of bound vars (others have no rule fvs)
        -- See Note [Finding rule RHS free vars]
        -- Why transClosureFV?  See Note [Loop breaker dependencies]
        rule_fv_env :: VarEnv VarSet
    rule_fv_env = VarEnv VarSet -> VarEnv VarSet
    transClosureFV (VarEnv VarSet -> VarEnv VarSet) -> VarEnv VarSet -> VarEnv VarSet
    forall a b. (a -> b) -> a -> b
    $ [(Id, VarSet)] -> VarEnv VarSet
    forall a. [(Id, a)] -> VarEnv a
    mkVarEnv ([(Id, VarSet)] -> VarEnv VarSet)
    -> [(Id, VarSet)] -> VarEnv VarSet
    forall a b. (a -> b) -> a -> b
    $
                      [ (Id
    b, VarSet
    rule_fvs)
                      | ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    b, nd_active_rule_fvs :: NodeDetails -> VarSet
    nd_active_rule_fvs = VarSet
    rule_fvs } <- [NodeDetails]
    details_s
                      , Bool -> Bool
    not (VarSet -> Bool
    isEmptyVarSet VarSet
    rule_fvs) ]

    {- Note [Loop breaker dependencies]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The loop breaker dependencies of x in a recursive
    group { f1 = e1; ...; fn = en } are:

    - The "inline free variables" of f: the fi free in
      f's stable unfolding and RHS; see Note [inl_fvs]

    - Any fi reachable from those inline free variables by a sequence
      of RULE rewrites.  Remember, rule rewriting is not affected
      by fi being a loop breaker, so we have to take the transitive
      closure in case f is the only possible loop breaker in the loop.

      Hence rule_fv_env.  We need only account for /active/ rules.
    -}

    ------------------------------------------
    nodeScore :: OccEnv
              -> Id        -- Binder with new occ-info
              -> VarSet    -- Loop-breaker dependencies
              -> NodeDetails
              -> NodeScore
    nodeScore :: OccEnv -> Id -> VarSet -> NodeDetails -> NodeScore
    nodeScore !OccEnv
    env Id
    new_bndr VarSet
    lb_deps
              (ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    old_bndr, nd_rhs :: NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs = WTUD TailUsageDetails
    _ CoreExpr
    bind_rhs })

      | Bool -> Bool
    not (Id -> Bool
    isId Id
    old_bndr)     -- A type or coercion variable is never a loop breaker
      = (JoinArity
    100, JoinArity
    0, Bool
    False)

      | Id
    old_bndr Id -> VarSet -> Bool
    `elemVarSet` VarSet
    lb_deps  -- Self-recursive things are great loop breakers
      = (JoinArity
    0, JoinArity
    0, Bool
    True)                   -- See Note [Self-recursion and loop breakers]

      | Bool -> Bool
    not (OccEnv -> Id -> Bool
    occ_unf_act OccEnv
    env Id
    old_bndr) -- A binder whose inlining is inactive (e.g. has
      = (JoinArity
    0, JoinArity
    0, Bool
    True)                   -- a NOINLINE pragma) makes a great loop breaker

      | CoreExpr -> Bool
    exprIsTrivial CoreExpr
    rhs
      = JoinArity -> NodeScore
    mk_score JoinArity
    10  -- Practically certain to be inlined
        -- Used to have also: && not (isExportedId bndr)
        -- But I found this sometimes cost an extra iteration when we have
        --      rec { d = (a,b); a = ...df...; b = ...df...; df = d }
        -- where df is the exported dictionary. Then df makes a really
        -- bad choice for loop breaker

      | DFunUnfolding { df_args :: Unfolding -> [CoreExpr]
    df_args = [CoreExpr]
    args } <- Unfolding
    old_unf
        -- Never choose a DFun as a loop breaker
        -- Note [DFuns should not be loop breakers]
      = (JoinArity
    9, [CoreExpr] -> JoinArity
    forall a. [a] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length [CoreExpr]
    args, Bool
    is_lb)

        -- Data structures are more important than INLINE pragmas
        -- so that dictionary/method recursion unravels

      | CoreUnfolding { uf_guidance :: Unfolding -> UnfoldingGuidance
    uf_guidance = UnfWhen {} } <- Unfolding
    old_unf
      = JoinArity -> NodeScore
    mk_score JoinArity
    6

      | CoreExpr -> Bool
    forall {b}. Expr b -> Bool
    is_con_app CoreExpr
    rhs   -- Data types help with cases:
      = JoinArity -> NodeScore
    mk_score JoinArity
    5       -- Note [Constructor applications]

      | Unfolding -> Bool
    isStableUnfolding Unfolding
    old_unf
      , Bool
    can_unfold
      = JoinArity -> NodeScore
    mk_score JoinArity
    3

      | OccInfo -> Bool
    isOneOcc (Id -> OccInfo
    idOccInfo Id
    new_bndr)
      = JoinArity -> NodeScore
    mk_score JoinArity
    2  -- Likely to be inlined

      | Bool
    can_unfold  -- The Id has some kind of unfolding
      = JoinArity -> NodeScore
    mk_score JoinArity
    1

      | Bool
    otherwise
      = (JoinArity
    0, JoinArity
    0, Bool
    is_lb)

      where
        mk_score :: Int -> NodeScore
        mk_score :: JoinArity -> NodeScore
    mk_score JoinArity
    rank = (JoinArity
    rank, JoinArity
    rhs_size, Bool
    is_lb)

        -- is_lb: see Note [Loop breakers, node scoring, and stability]
        is_lb :: Bool
    is_lb = OccInfo -> Bool
    isStrongLoopBreaker (Id -> OccInfo
    idOccInfo Id
    old_bndr)

        old_unf :: Unfolding
    old_unf = IdUnfoldingFun
    realIdUnfolding Id
    old_bndr
        can_unfold :: Bool
    can_unfold = Unfolding -> Bool
    canUnfold Unfolding
    old_unf
        rhs :: CoreExpr
    rhs        = case Unfolding
    old_unf of
                       CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src, uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    unf_rhs }
                         | UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src
                         -> CoreExpr
    unf_rhs
                       Unfolding
    _ -> CoreExpr
    bind_rhs
           -- 'bind_rhs' is irrelevant for inlining things with a stable unfolding
        rhs_size :: JoinArity
    rhs_size = case Unfolding
    old_unf of
                     CoreUnfolding { uf_guidance :: Unfolding -> UnfoldingGuidance
    uf_guidance = UnfoldingGuidance
    guidance }
                        | UnfIfGoodArgs { ug_size :: UnfoldingGuidance -> JoinArity
    ug_size = JoinArity
    size } <- UnfoldingGuidance
    guidance
                        -> JoinArity
    size
                     Unfolding
    _  -> CoreExpr -> JoinArity
    cheapExprSize CoreExpr
    rhs

            -- Checking for a constructor application
            -- Cheap and cheerful; the simplifier moves casts out of the way
            -- The lambda case is important to spot x = /\a. C (f a)
            -- which comes up when C is a dictionary constructor and
            -- f is a default method.
            -- Example: the instance for Show (ST s a) in GHC.ST
            --
            -- However we *also* treat (\x. C p q) as a con-app-like thing,
            --      Note [Closure conversion]
        is_con_app :: Expr b -> Bool
    is_con_app (Var Id
    v)    = Id -> Bool
    isConLikeId Id
    v
        is_con_app (App Expr b
    f Expr b
    _)  = Expr b -> Bool
    is_con_app Expr b
    f
        is_con_app (Lam b
    _ Expr b
    e)  = Expr b -> Bool
    is_con_app Expr b
    e
        is_con_app (Tick CoreTickish
    _ Expr b
    e) = Expr b -> Bool
    is_con_app Expr b
    e
        is_con_app (Let Bind b
    _ Expr b
    e)  = Expr b -> Bool
    is_con_app Expr b
    e  -- let x = let y = blah in (a,b)
        is_con_app Expr b
    _          = Bool
    False         -- We will float the y out, so treat
                                              -- the x-binding as a con-app (#20941)

    maxExprSize :: Int
    maxExprSize :: JoinArity
    maxExprSize = JoinArity
    20  -- Rather arbitrary

    cheapExprSize :: CoreExpr -> Int
    -- Maxes out at maxExprSize
    cheapExprSize :: CoreExpr -> JoinArity
    cheapExprSize CoreExpr
    e
      = JoinArity -> CoreExpr -> JoinArity
    go JoinArity
    0 CoreExpr
    e
      where
        go :: JoinArity -> CoreExpr -> JoinArity
    go JoinArity
    n CoreExpr
    e | JoinArity
    n JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    maxExprSize = JoinArity
    n
               | Bool
    otherwise        = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e

        go1 :: JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n (Var {})        = JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
        go1 JoinArity
    n (Lit {})        = JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1
        go1 JoinArity
    n (Type {})       = JoinArity
    n
        go1 JoinArity
    n (Coercion {})   = JoinArity
    n
        go1 JoinArity
    n (Tick CoreTickish
    _ CoreExpr
    e)      = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
        go1 JoinArity
    n (Cast CoreExpr
    e CoercionR
    _)      = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
        go1 JoinArity
    n (App CoreExpr
    f CoreExpr
    a)       = JoinArity -> CoreExpr -> JoinArity
    go (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    f) CoreExpr
    a
        go1 JoinArity
    n (Lam Id
    b CoreExpr
    e)
          | Id -> Bool
    isTyVar Id
    b         = JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e
          | Bool
    otherwise         = JoinArity -> CoreExpr -> JoinArity
    go (JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    +JoinArity
    1) CoreExpr
    e
        go1 JoinArity
    n (Let CoreBind
    b CoreExpr
    e)       = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) (CoreBind -> [CoreExpr]
    forall b. Bind b -> [Expr b]
    rhssOfBind CoreBind
    b)
        go1 JoinArity
    n (Case CoreExpr
    e Id
    _ Type
    _ [Alt Id]
    as) = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) ([Alt Id] -> [CoreExpr]
    forall b. [Alt b] -> [Expr b]
    rhssOfAlts [Alt Id]
    as)

        gos :: JoinArity -> [CoreExpr] -> JoinArity
    gos JoinArity
    n [] = JoinArity
    n
        gos JoinArity
    n (CoreExpr
    e:[CoreExpr]
    es) | JoinArity
    n JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    >= JoinArity
    maxExprSize = JoinArity
    n
                     | Bool
    otherwise        = JoinArity -> [CoreExpr] -> JoinArity
    gos (JoinArity -> CoreExpr -> JoinArity
    go1 JoinArity
    n CoreExpr
    e) [CoreExpr]
    es

    betterLB :: NodeScore -> NodeScore -> Bool
    -- If  n1 `betterLB` n2  then choose n1 as the loop breaker
    betterLB :: NodeScore -> NodeScore -> Bool
    betterLB (JoinArity
    rank1, JoinArity
    size1, Bool
    lb1) (JoinArity
    rank2, JoinArity
    size2, Bool
    _)
      | JoinArity
    rank1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    < JoinArity
    rank2 = Bool
    True
      | JoinArity
    rank1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    rank2 = Bool
    False
      | JoinArity
    size1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    < JoinArity
    size2 = Bool
    False   -- Make the bigger n2 into the loop breaker
      | JoinArity
    size1 JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    size2 = Bool
    True
      | Bool
    lb1           = Bool
    True    -- Tie-break: if n1 was a loop breaker before, choose it
      | Bool
    otherwise     = Bool
    False   -- See Note [Loop breakers, node scoring, and stability]

    {- Note [Self-recursion and loop breakers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If we have
       rec { f = ...f...g...
           ; g = .....f...   }
    then 'f' has to be a loop breaker anyway, so we may as well choose it
    right away, so that g can inline freely.

    This is really just a cheap hack. Consider
       rec { f = ...g...
           ; g = ..f..h...
          ;  h = ...f....}
    Here f or g are better loop breakers than h; but we might accidentally
    choose h.  Finding the minimal set of loop breakers is hard.

    Note [Loop breakers, node scoring, and stability]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    To choose a loop breaker, we give a NodeScore to each node in the SCC,
    and pick the one with the best score (according to 'betterLB').

    We need to be jolly careful (#12425, #12234) about the stability
    of this choice. Suppose we have

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...f..
          False -> ..f...

    In each iteration of the simplifier the occurrence analyser OccAnal
    chooses a loop breaker. Suppose in iteration 1 it choose g as the loop
    breaker. That means it is free to inline f.

    Suppose that GHC decides to inline f in the branches of the case, but
    (for some reason; eg it is not saturated) in the rhs of g. So we get

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...g...g.....
          False -> ..g..g....

    Now suppose that, for some reason, in the next iteration the occurrence
    analyser chooses f as the loop breaker, so it can freely inline g. And
    again for some reason the simplifier inlines g at its calls in the case
    branches, but not in the RHS of f. Then we get

        let rec { f = ...g...g...
                ; g = ...f...f... }
        in
        case x of
          True  -> ...(...f...f...)...(...f..f..).....
          False -> ..(...f...f...)...(..f..f...)....

    You can see where this is going! Each iteration of the simplifier
    doubles the number of calls to f or g. No wonder GHC is slow!

    (In the particular example in comment:3 of #12425, f and g are the two
    mutually recursive fmap instances for CondT and Result. They are both
    marked INLINE which, oddly, is why they don't inline in each other's
    RHS, because the call there is not saturated.)

    The root cause is that we flip-flop on our choice of loop breaker. I
    always thought it didn't matter, and indeed for any single iteration
    to terminate, it doesn't matter. But when we iterate, it matters a
    lot!!

    So The Plan is this:
       If there is a tie, choose the node that
       was a loop breaker last time round

    Hence the is_lb field of NodeScore
    -}

    {- *********************************************************************
    *                                                                      *
                      Lambda groups
    *                                                                      *
    ********************************************************************* -}

    {- Note [Occurrence analysis for lambda binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For value lambdas we do a special hack.  Consider
         (\x. \y. ...x...)
    If we did nothing, x is used inside the \y, so would be marked
    as dangerous to dup.  But in the common case where the abstraction
    is applied to two arguments this is over-pessimistic, which delays
    inlining x, which forces more simplifier iterations.

    So the occurrence analyser collaborates with the simplifier to treat
    a /lambda-group/ specially.   A lambda-group is a contiguous run of
    lambda and casts, e.g.
        Lam x (Lam y (Cast (Lam z body) co))

    * Occurrence analyser: we just mark each binder in the lambda-group
      (here: x,y,z) with its occurrence info in the *body* of the
      lambda-group.  See occAnalLamTail.

    * Simplifier.  The simplifier is careful when partially applying
      lambda-groups. See the call to zapLambdaBndrs in
         GHC.Core.Opt.Simplify.simplExprF1
         GHC.Core.SimpleOpt.simple_app

    * Why do we take care to account for intervening casts? Answer:
      currently we don't do eta-expansion and cast-swizzling in a stable
      unfolding (see Historical-note [Eta-expansion in stable unfoldings]).
      So we can get
        f = \x. ((\y. ...x...y...) |> co)
      Now, since the lambdas aren't together, the occurrence analyser will
      say that x is OnceInLam.  Now if we have a call
        (f e1 |> co) e2
      we'll end up with
        let x = e1 in ...x..e2...
      and it'll take an extra iteration of the Simplifier to substitute for x.

    A thought: a lambda-group is pretty much what GHC.Core.Opt.Arity.manifestArity
    recognises except that the latter looks through (some) ticks.  Maybe a lambda
    group should also look through (some) ticks?
    -}

    isOneShotFun :: CoreExpr -> Bool
    -- The top level lambdas, ignoring casts, of the expression
    -- are all one-shot.  If there aren't any lambdas at all, this is True
    isOneShotFun :: CoreExpr -> Bool
    isOneShotFun (Lam Id
    b CoreExpr
    e)  = Id -> Bool
    isOneShotBndr Id
    b Bool -> Bool -> Bool
    && CoreExpr -> Bool
    isOneShotFun CoreExpr
    e
    isOneShotFun (Cast CoreExpr
    e CoercionR
    _) = CoreExpr -> Bool
    isOneShotFun CoreExpr
    e
    isOneShotFun CoreExpr
    _          = Bool
    True

    zapLambdaBndrs :: CoreExpr -> FullArgCount -> CoreExpr
    -- If (\xyz. t) appears under-applied to only two arguments,
    -- we must zap the occ-info on x,y, because they appear under the \z
    -- See Note [Occurrence analysis for lambda binders] in GHc.Core.Opt.OccurAnal
    --
    -- NB: `arg_count` includes both type and value args
    zapLambdaBndrs :: CoreExpr -> JoinArity -> CoreExpr
    zapLambdaBndrs CoreExpr
    fun JoinArity
    arg_count
      = -- If the lambda is fully applied, leave it alone; if not
        -- zap the OccInfo on the lambdas that do have arguments,
        -- so they beta-reduce to use-many Lets rather than used-once ones.
        JoinArity -> CoreExpr -> Maybe CoreExpr
    zap JoinArity
    arg_count CoreExpr
    fun Maybe CoreExpr -> CoreExpr -> CoreExpr
    forall a. Maybe a -> a -> a
    `orElse` CoreExpr
    fun
      where
        zap :: FullArgCount -> CoreExpr -> Maybe CoreExpr
        -- Nothing => No need to change the occ-info
        -- Just e  => Had to change
        zap :: JoinArity -> CoreExpr -> Maybe CoreExpr
    zap JoinArity
    0 CoreExpr
    e | CoreExpr -> Bool
    isOneShotFun CoreExpr
    e = Maybe CoreExpr
    forall a. Maybe a
    Nothing  -- All remaining lambdas are one-shot
                | Bool
    otherwise      = CoreExpr -> Maybe CoreExpr
    forall a. a -> Maybe a
    Just CoreExpr
    e   -- in which case no need to zap
        zap JoinArity
    n (Cast CoreExpr
    e CoercionR
    co) = do { e' <- JoinArity -> CoreExpr -> Maybe CoreExpr
    zap JoinArity
    n CoreExpr
    e; return (Cast e' co) }
        zap JoinArity
    n (Lam Id
    b CoreExpr
    e)   = do { e' <- JoinArity -> CoreExpr -> Maybe CoreExpr
    zap (JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    -JoinArity
    1) CoreExpr
    e
                               ; return (Lam (zap_bndr b) e') }
        zap JoinArity
    _ CoreExpr
    _           = Maybe CoreExpr
    forall a. Maybe a
    Nothing  -- More arguments than lambdas

        zap_bndr :: Id -> Id
    zap_bndr Id
    b | Id -> Bool
    isTyVar Id
    b = Id
    b
                   | Bool
    otherwise = Id -> Id
    zapLamIdInfo Id
    b

    occAnalLamTail :: OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    -- ^ See Note [Occurrence analysis for lambda binders].
    -- It does the following:
    --   * Sets one-shot info on the lambda binder from the OccEnv, and
    --     removes that one-shot info from the OccEnv
    --   * Sets the OccEnv to OccVanilla when going under a value lambda
    --   * Tags each lambda with its occurrence information
    --   * Walks through casts
    --   * Package up the analysed lambda with its manifest join arity
    --
    -- This function does /not/ do
    --   markAllInsideLam or
    --   markAllNonTail
    -- The caller does that, via adjustTailUsage (mostly calls go through
    -- adjustNonRecRhs). Every call to occAnalLamTail must ultimately call
    -- adjustTailUsage to discharge the assumed join arity.
    --
    -- In effect, the analysis result is for a non-recursive join point with
    -- manifest arity and adjustTailUsage does the fixup.
    -- See Note [Adjusting right-hand sides]
    occAnalLamTail :: OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    env CoreExpr
    expr
      = let !(WUD UsageDetails
    usage CoreExpr
    expr') = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occ_anal_lam_tail OccEnv
    env CoreExpr
    expr
        in TailUsageDetails -> CoreExpr -> WithTailUsageDetails CoreExpr
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD (CoreExpr -> JoinArity
    joinRhsArity CoreExpr
    expr) UsageDetails
    usage) CoreExpr
    expr'

    occ_anal_lam_tail :: OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    -- Does not markInsideLam etc for the outmost batch of lambdas
    occ_anal_lam_tail :: OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occ_anal_lam_tail OccEnv
    env expr :: CoreExpr
    expr@(Lam {})
      = OccEnv -> [Id] -> CoreExpr -> WithUsageDetails CoreExpr
    go OccEnv
    env [] CoreExpr
    expr
      where
        go :: OccEnv -> [Var] -> CoreExpr -> WithUsageDetails CoreExpr
        go :: OccEnv -> [Id] -> CoreExpr -> WithUsageDetails CoreExpr
    go OccEnv
    env [Id]
    rev_bndrs (Lam Id
    bndr CoreExpr
    body)
          | Id -> Bool
    isTyVar Id
    bndr
          = OccEnv -> [Id] -> CoreExpr -> WithUsageDetails CoreExpr
    go OccEnv
    env (Id
    bndrId -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    rev_bndrs) CoreExpr
    body
                  -- Important: Unlike a value binder, do not modify occ_encl
                  -- to OccVanilla, so that with a RHS like
                  --   \(@ x) -> K @x (f @x)
                  -- we'll see that (K @x (f @x)) is in a OccRhs, and hence refrain
                  -- from inlining f. See the beginning of Note [Cascading inlines].

          | Bool
    otherwise
          = let ([OneShotInfo]
    env_one_shots', Id
    bndr')
                  = case OccEnv -> [OneShotInfo]
    occ_one_shots OccEnv
    env of
                      []         -> ([],  Id
    bndr)
                      (OneShotInfo
    os : [OneShotInfo]
    oss) -> ([OneShotInfo]
    oss, Id -> OneShotInfo -> Id
    updOneShotInfo Id
    bndr OneShotInfo
    os)
                      -- Use updOneShotInfo, not setOneShotInfo, as pre-existing
                      -- one-shot info might be better than what we can infer, e.g.
                      -- due to explicit use of the magic 'oneShot' function.
                      -- See Note [oneShot magic]
                env' :: OccEnv
    env' = OccEnv
    env { occ_encl = OccVanilla, occ_one_shots = env_one_shots' }
             in OccEnv -> [Id] -> CoreExpr -> WithUsageDetails CoreExpr
    go OccEnv
    env' (Id
    bndr'Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    rev_bndrs) CoreExpr
    body

        go OccEnv
    env [Id]
    rev_bndrs CoreExpr
    body
          = OccEnv
    -> [Id]
    -> (OccEnv -> WithUsageDetails CoreExpr)
    -> WithUsageDetails CoreExpr
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScope OccEnv
    env [Id]
    rev_bndrs ((OccEnv -> WithUsageDetails CoreExpr)
     -> WithUsageDetails CoreExpr)
    -> (OccEnv -> WithUsageDetails CoreExpr)
    -> WithUsageDetails CoreExpr
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
            let !(WUD UsageDetails
    usage CoreExpr
    body') = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occ_anal_lam_tail OccEnv
    env CoreExpr
    body
                wrap_lam :: CoreExpr -> Id -> CoreExpr
    wrap_lam CoreExpr
    body Id
    bndr = Id -> CoreExpr -> CoreExpr
    forall b. b -> Expr b -> Expr b
    Lam (UsageDetails -> Id -> Id
    tagLamBinder UsageDetails
    usage Id
    bndr) CoreExpr
    body
            in UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails
    usage UsageDetails -> [Id] -> UsageDetails
    `addLamCoVarOccs` [Id]
    rev_bndrs)
                   ((CoreExpr -> Id -> CoreExpr) -> CoreExpr -> [Id] -> CoreExpr
    forall b a. (b -> a -> b) -> b -> [a] -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' CoreExpr -> Id -> CoreExpr
    wrap_lam CoreExpr
    body' [Id]
    rev_bndrs)

    -- For casts, keep going in the same lambda-group
    -- See Note [Occurrence analysis for lambda binders]
    occ_anal_lam_tail OccEnv
    env (Cast CoreExpr
    expr CoercionR
    co)
      = let  WUD UsageDetails
    usage CoreExpr
    expr' = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occ_anal_lam_tail OccEnv
    env CoreExpr
    expr
             -- usage1: see Note [Gather occurrences of coercion variables]
             usage1 :: UsageDetails
    usage1 = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage (CoercionR -> VarSet
    coVarsOfCo CoercionR
    co)

             -- usage2: see Note [Occ-anal and cast worker/wrapper]
             usage2 :: UsageDetails
    usage2 = case CoreExpr
    expr of
                        Var {} | OccEnv -> Bool
    isRhsEnv OccEnv
    env -> UsageDetails -> UsageDetails
    markAllMany UsageDetails
    usage1
                        CoreExpr
    _ -> UsageDetails
    usage1

             -- usage3: you might think this was not necessary, because of
             -- the markAllNonTail in adjustTailUsage; but not so!  For a
             -- join point, adjustTailUsage doesn't do this; yet if there is
             -- a cast, we must!  Also: why markAllNonTail?  See
             -- GHC.Core.Lint: Note Note [Join points and casts]
             usage3 :: UsageDetails
    usage3 = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    usage2

        in UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    usage3 (CoreExpr -> CoercionR -> CoreExpr
    forall b. Expr b -> CoercionR -> Expr b
    Cast CoreExpr
    expr' CoercionR
    co)

    occ_anal_lam_tail OccEnv
    env CoreExpr
    expr  -- Not Lam, not Cast
      = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    expr

    {- Note [Occ-anal and cast worker/wrapper]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider   y = e; x = y |> co
    If we mark y as used-once, we'll inline y into x, and the Cast
    worker/wrapper transform will float it straight back out again.  See
    Note [Cast worker/wrapper] in GHC.Core.Opt.Simplify.

    So in this particular case we want to mark 'y' as Many.  It's very
    ad-hoc, but it's also simple.  It's also what would happen if we gave
    the binding for x a stable unfolding (as we usually do for wrappers, thus
          y = e
          {-# INLINE x #-}
          x = y |> co
    Now y appears twice -- once in x's stable unfolding, and once in x's
    RHS. So it'll get a Many occ-info.  (Maybe Cast w/w should create a stable
    unfolding, which would obviate this Note; but that seems a bit of a
    heavyweight solution.)

    We only need to this in occAnalLamTail, not occAnal, because the top leve
    of a right hand side is handled by occAnalLamTail.
    -}

    {- *********************************************************************
    *                                                                      *
                       Right hand sides
    *                                                                      *
    ********************************************************************* -}

    occAnalUnfolding :: OccEnv
                     -> Unfolding
                     -> WithTailUsageDetails Unfolding
    -- Occurrence-analyse a stable unfolding;
    -- discard a non-stable one altogether and return empty usage details.
    occAnalUnfolding :: OccEnv -> Unfolding -> WithTailUsageDetails Unfolding
    occAnalUnfolding !OccEnv
    env Unfolding
    unf
      = case Unfolding
    unf of
          unf :: Unfolding
    unf@(CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    rhs, uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src })
            | UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src ->
                let
                  WTUD (TUD JoinArity
    rhs_ja UsageDetails
    uds) CoreExpr
    rhs' = OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    env CoreExpr
    rhs
                  unf' :: Unfolding
    unf' = Unfolding
    unf { uf_tmpl = rhs' }
                in TailUsageDetails -> Unfolding -> WithTailUsageDetails Unfolding
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    rhs_ja (UsageDetails -> UsageDetails
    markAllMany UsageDetails
    uds)) Unfolding
    unf'
                  -- markAllMany: see Note [Occurrences in stable unfoldings]

            | Bool
    otherwise -> TailUsageDetails -> Unfolding -> WithTailUsageDetails Unfolding
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    0 UsageDetails
    emptyDetails) Unfolding
    unf
                  -- For non-Stable unfoldings we leave them undisturbed, but
                  -- don't count their usage because the simplifier will discard them.
                  -- We leave them undisturbed because nodeScore uses their size info
                  -- to guide its decisions.  It's ok to leave un-substituted
                  -- expressions in the tree because all the variables that were in
                  -- scope remain in scope; there is no cloning etc.

          unf :: Unfolding
    unf@(DFunUnfolding { df_bndrs :: Unfolding -> [Id]
    df_bndrs = [Id]
    bndrs, df_args :: Unfolding -> [CoreExpr]
    df_args = [CoreExpr]
    args })
            -> let WUD UsageDetails
    uds [CoreExpr]
    args' = OccEnv
    -> [Id]
    -> (OccEnv -> WithUsageDetails [CoreExpr])
    -> WithUsageDetails [CoreExpr]
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env [Id]
    bndrs ((OccEnv -> WithUsageDetails [CoreExpr])
     -> WithUsageDetails [CoreExpr])
    -> (OccEnv -> WithUsageDetails [CoreExpr])
    -> WithUsageDetails [CoreExpr]
    forall a b. (a -> b) -> a -> b
    $ \ OccEnv
    env ->
                                   OccEnv -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    occAnalList OccEnv
    env [CoreExpr]
    args
               in TailUsageDetails -> Unfolding -> WithTailUsageDetails Unfolding
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    0 UsageDetails
    uds) (Unfolding
    unf { df_args = args' })
                  -- No need to use tagLamBinders because we
                  -- never inline DFuns so the occ-info on binders doesn't matter

          Unfolding
    unf -> TailUsageDetails -> Unfolding -> WithTailUsageDetails Unfolding
    forall a. TailUsageDetails -> a -> WithTailUsageDetails a
    WTUD (JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    0 UsageDetails
    emptyDetails) Unfolding
    unf

    occAnalRule :: OccEnv
                 -> CoreRule
                 -> (CoreRule,         -- Each (non-built-in) rule
                     UsageDetails,     -- Usage details for LHS
                     TailUsageDetails) -- Usage details for RHS
    occAnalRule :: OccEnv -> CoreRule -> (CoreRule, UsageDetails, TailUsageDetails)
    occAnalRule OccEnv
    env rule :: CoreRule
    rule@(Rule { ru_bndrs :: CoreRule -> [Id]
    ru_bndrs = [Id]
    bndrs, ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args, ru_rhs :: CoreRule -> CoreExpr
    ru_rhs = CoreExpr
    rhs })
      = (CoreRule
    rule', UsageDetails
    lhs_uds', JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    rhs_ja UsageDetails
    rhs_uds')
      where
        rule' :: CoreRule
    rule' = CoreRule
    rule { ru_args = args', ru_rhs = rhs' }

        WUD UsageDetails
    lhs_uds [CoreExpr]
    args' = OccEnv
    -> [Id]
    -> (OccEnv -> WithUsageDetails [CoreExpr])
    -> WithUsageDetails [CoreExpr]
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env [Id]
    bndrs ((OccEnv -> WithUsageDetails [CoreExpr])
     -> WithUsageDetails [CoreExpr])
    -> (OccEnv -> WithUsageDetails [CoreExpr])
    -> WithUsageDetails [CoreExpr]
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
                            OccEnv -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    occAnalList OccEnv
    env [CoreExpr]
    args

        lhs_uds' :: UsageDetails
    lhs_uds' = UsageDetails -> UsageDetails
    markAllManyNonTail UsageDetails
    lhs_uds
        WUD UsageDetails
    rhs_uds CoreExpr
    rhs' = OccEnv
    -> [Id]
    -> (OccEnv -> WithUsageDetails CoreExpr)
    -> WithUsageDetails CoreExpr
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env [Id]
    bndrs ((OccEnv -> WithUsageDetails CoreExpr)
     -> WithUsageDetails CoreExpr)
    -> (OccEnv -> WithUsageDetails CoreExpr)
    -> WithUsageDetails CoreExpr
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
                           OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    rhs
                              -- Note [Rules are extra RHSs]
                              -- Note [Rule dependency info]
        rhs_uds' :: UsageDetails
    rhs_uds' = UsageDetails -> UsageDetails
    markAllMany UsageDetails
    rhs_uds
        rhs_ja :: JoinArity
    rhs_ja = [CoreExpr] -> JoinArity
    forall a. [a] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length [CoreExpr]
    args -- See Note [Join points and unfoldings/rules]

    occAnalRule OccEnv
    _ CoreRule
    other_rule = (CoreRule
    other_rule, UsageDetails
    emptyDetails, JoinArity -> UsageDetails -> TailUsageDetails
    TUD JoinArity
    0 UsageDetails
    emptyDetails)

    {- Note [Occurrences in stable unfoldings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        f p = BIG
        {-# INLINE g #-}
        g y = not (f y)
    where this is the /only/ occurrence of 'f'.  So 'g' will get a stable
    unfolding.  Now suppose that g's RHS gets optimised (perhaps by a rule
    or inlining f) so that it doesn't mention 'f' any more.  Now the last
    remaining call to f is in g's Stable unfolding. But, even though there
    is only one syntactic occurrence of f, we do /not/ want to do
    preinlineUnconditionally here!

    The INLINE pragma says "inline exactly this RHS"; perhaps the
    programmer wants to expose that 'not', say. If we inline f that will make
    the Stable unfoldign big, and that wasn't what the programmer wanted.

    Another way to think about it: if we inlined g as-is into multiple
    call sites, now there's be multiple calls to f.

    Bottom line: treat all occurrences in a stable unfolding as "Many".
    We still leave tail call information intact, though, as to not spoil
    potential join points.

    Note [Unfoldings and rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Generally unfoldings and rules are already occurrence-analysed, so we
    don't want to reconstruct their trees; we just want to analyse them to
    find how they use their free variables.

    EXCEPT if there is a binder-swap going on, in which case we do want to
    produce a new tree.

    So we have a fast-path that keeps the old tree if the occ_bs_env is
    empty.   This just saves a bit of allocation and reconstruction; not
    a big deal.

    Two tricky corners:

    * Dead bindings (#22761). Supose we have
        Unfolding = \x. let y = foo in x+1
      which includes a dead binding for `y`. In occAnalUnfolding we occ-anal
      the unfolding and produce /no/ occurrences of `foo` (since `y` is
      dead).  But if we discard the occ-analysed syntax tree (which we do on
      our fast path), and use the old one, we still /have/ an occurrence of
      `foo` -- and that can lead to out-of-scope variables (#22761).

      Solution: always keep occ-analysed trees in unfoldings and rules, so they
      have no dead code.  See Note [OccInfo in unfoldings and rules] in GHC.Core.

    * One-shot binders. Consider
         {- f has Stable unfolding \p q -> blah
            Demand on f is LC(L,C(1,!P(L)); that is, one-shot in its second ar -}
         f = \x y. blah

       Now we `mkRhsOccEnv` will build an OccEnv for f's RHS that has
              occ_one_shots = [NoOneShortInfo, OneShotLam]
       This will put OneShotLam on the \y.  And it'll put it on the \q.  But the
       noBinderSwap check will mean that we discard this new occ-anal'd unfolding
       and keep the old one, with no OneShotInfo.

       This looks a little inconsistent, but the Stable unfolding is just used for
       inlinings; OneShotInfo isn't a lot of use here.

    Note [Cascading inlines]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    By default we use an OccRhs for the RHS of a binding.  This tells the
    occ anal n that it's looking at an RHS, which has an effect in
    occAnalApp.  In particular, for constructor applications, it makes
    the arguments appear to have NoOccInfo, so that we don't inline into
    them. Thus    x = f y
                  k = Just x
    we do not want to inline x.

    But there's a problem.  Consider
         x1 = a0 : []
         x2 = a1 : x1
         x3 = a2 : x2
         g  = f x3
    First time round, it looks as if x1 and x2 occur as an arg of a
    let-bound constructor ==> give them a many-occurrence.
    But then x3 is inlined (unconditionally as it happens) and
    next time round, x2 will be, and the next time round x1 will be
    Result: multiple simplifier iterations.  Sigh.

    So, when analysing the RHS of x3 we notice that x3 will itself
    definitely inline the next time round, and so we analyse x3's rhs in
    an OccVanilla context, not OccRhs.  Hence the "certainly_inline" stuff.

    Annoyingly, we have to approximate GHC.Core.Opt.Simplify.Utils.preInlineUnconditionally.
    If (a) the RHS is expandable (see isExpandableApp in occAnalApp), and
       (b) certainly_inline says "yes" when preInlineUnconditionally says "no"
    then the simplifier iterates indefinitely:
            x = f y
            k = Just x   -- We decide that k is 'certainly_inline'
            v = ...k...  -- but preInlineUnconditionally doesn't inline it
    inline ==>
            k = Just (f y)
            v = ...k...
    float ==>
            x1 = f y
            k = Just x1
            v = ...k...

    This is worse than the slow cascade, so we only want to say "certainly_inline"
    if it really is certain.  Look at the note with preInlineUnconditionally
    for the various clauses.

    ************************************************************************
    *                                                                      *
                    Expressions
    *                                                                      *
    ************************************************************************
    -}

    occAnalList :: OccEnv -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    occAnalList :: OccEnv -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    occAnalList !OccEnv
    _   []    = UsageDetails -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    emptyDetails []
    occAnalList OccEnv
    env (CoreExpr
    e:[CoreExpr]
    es) = let
                              (WUD UsageDetails
    uds1 CoreExpr
    e') = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    e
                              (WUD UsageDetails
    uds2 [CoreExpr]
    es') = OccEnv -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    occAnalList OccEnv
    env [CoreExpr]
    es
                             in UsageDetails -> [CoreExpr] -> WithUsageDetails [CoreExpr]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails
    uds1 UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    uds2) (CoreExpr
    e' CoreExpr -> [CoreExpr] -> [CoreExpr]
    forall a. a -> [a] -> [a]
    : [CoreExpr]
    es')

    occAnal :: OccEnv
            -> CoreExpr
            -> WithUsageDetails CoreExpr       -- Gives info only about the "interesting" Ids

    occAnal :: OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal !OccEnv
    _   expr :: CoreExpr
    expr@(Lit Literal
    _)  = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    emptyDetails CoreExpr
    expr

    occAnal OccEnv
    env expr :: CoreExpr
    expr@(Var Id
    _) = OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> WithUsageDetails CoreExpr
    occAnalApp OccEnv
    env (CoreExpr
    expr, [], [])
        -- At one stage, I gathered the idRuleVars for the variable here too,
        -- which in a way is the right thing to do.
        -- But that went wrong right after specialisation, when
        -- the *occurrences* of the overloaded function didn't have any
        -- rules in them, so the *specialised* versions looked as if they
        -- weren't used at all.

    occAnal OccEnv
    _ expr :: CoreExpr
    expr@(Type Type
    ty)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    emptyDetails (Type -> VarSet
    coVarsOfType Type
    ty)) CoreExpr
    expr
    occAnal OccEnv
    _ expr :: CoreExpr
    expr@(Coercion CoercionR
    co)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    emptyDetails (CoercionR -> VarSet
    coVarsOfCo CoercionR
    co)) CoreExpr
    expr
            -- See Note [Gather occurrences of coercion variables]

    {- Note [Gather occurrences of coercion variables]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We need to gather info about what coercion variables appear, for two reasons:

    1. So that we can sort them into the right place when doing dependency analysis.

    2. So that we know when they are surely dead.

    It is useful to know when they a coercion variable is surely dead,
    when we want to discard a case-expression, in GHC.Core.Opt.Simplify.rebuildCase.
    For example (#20143):

      case unsafeEqualityProof @blah of
         UnsafeRefl cv -> ...no use of cv...

    Here we can discard the case, since unsafeEqualityProof always terminates.
    But only if the coercion variable 'cv' is unused.

    Another example from #15696: we had something like
      case eq_sel d of co -> ...(typeError @(...co...) "urk")...
    Then 'd' was substituted by a dictionary, so the expression
    simpified to
      case (Coercion <blah>) of cv -> ...(typeError @(...cv...) "urk")...

    We can only  drop the case altogether if 'cv' is unused, which is not
    the case here.

    Conclusion: we need accurate dead-ness info for CoVars.
    We gather CoVar occurrences from:

      * The (Type ty) and (Coercion co) cases of occAnal

      * The type 'ty' of a lambda-binder (\(x:ty). blah)
        See addCoVarOccs

    But it is not necessary to gather CoVars from the types of other binders.

    * For let-binders, if the type mentions a CoVar, so will the RHS (since
      it has the same type)

    * For case-alt binders, if the type mentions a CoVar, so will the scrutinee
      (since it has the same type)
    -}

    occAnal OccEnv
    env (Tick CoreTickish
    tickish CoreExpr
    body)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    usage' (CoreTickish -> CoreExpr -> CoreExpr
    forall b. CoreTickish -> Expr b -> Expr b
    Tick CoreTickish
    tickish CoreExpr
    body')
      where
        WUD UsageDetails
    usage CoreExpr
    body' = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    body

        usage' :: UsageDetails
    usage'
          | CoreTickish
    tickish CoreTickish -> TickishScoping -> Bool
    forall (pass :: TickishPass).
    GenTickish pass -> TickishScoping -> Bool
    `tickishScopesLike` TickishScoping
    SoftScope
          = UsageDetails
    usage  -- For soft-scoped ticks (including SourceNotes) we don't want
                   -- to lose join-point-hood, so we don't mess with `usage` (#24078)

          -- For a non-soft tick scope, we can inline lambdas only, so we
          -- abandon tail calls, and do markAllInsideLam too: usage_lam

          |  Breakpoint XBreakpoint 'TickishPassCore
    _ JoinArity
    _ [XTickishId 'TickishPassCore]
    ids Module
    _ <- CoreTickish
    tickish
          = -- Never substitute for any of the Ids in a Breakpoint
            UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage_lam ([Id] -> VarSet
    mkVarSet [Id]
    [XTickishId 'TickishPassCore]
    ids)

          | Bool
    otherwise
          = UsageDetails
    usage_lam

        usage_lam :: UsageDetails
    usage_lam = UsageDetails -> UsageDetails
    markAllNonTail (UsageDetails -> UsageDetails
    markAllInsideLam UsageDetails
    usage)

        -- TODO There may be ways to make ticks and join points play
        -- nicer together, but right now there are problems:
        --   let j x = ... in tick<t> (j 1)
        -- Making j a join point may cause the simplifier to drop t
        -- (if the tick is put into the continuation). So we don't
        -- count j 1 as a tail call.
        -- See #14242.

    occAnal OccEnv
    env (Cast CoreExpr
    expr CoercionR
    co)
      = let  (WUD UsageDetails
    usage CoreExpr
    expr') = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    expr
             usage1 :: UsageDetails
    usage1 = UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    usage (CoercionR -> VarSet
    coVarsOfCo CoercionR
    co)
                 -- usage2: see Note [Gather occurrences of coercion variables]
             usage2 :: UsageDetails
    usage2 = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    usage1
                 -- usage3: calls inside expr aren't tail calls any more
        in UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    usage2 (CoreExpr -> CoercionR -> CoreExpr
    forall b. Expr b -> CoercionR -> Expr b
    Cast CoreExpr
    expr' CoercionR
    co)

    occAnal OccEnv
    env app :: CoreExpr
    app@(App CoreExpr
    _ CoreExpr
    _)
      = OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> WithUsageDetails CoreExpr
    occAnalApp OccEnv
    env ((CoreTickish -> Bool)
    -> CoreExpr -> (CoreExpr, [CoreExpr], [CoreTickish])
    forall b.
    (CoreTickish -> Bool)
    -> Expr b -> (Expr b, [Expr b], [CoreTickish])
    collectArgsTicks CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable CoreExpr
    app)

    occAnal OccEnv
    env expr :: CoreExpr
    expr@(Lam {})
      = JoinPointHood
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    adjustNonRecRhs JoinPointHood
    NotJoinPoint (WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr)
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    forall a b. (a -> b) -> a -> b
    $ -- NotJoinPoint <=> markAllManyNonTail
        OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    env CoreExpr
    expr

    occAnal OccEnv
    env (Case CoreExpr
    scrut Id
    bndr Type
    ty [Alt Id]
    alts)
      = let
          WUD UsageDetails
    scrut_usage CoreExpr
    scrut' = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal (OccEnv -> [Alt Id] -> OccEnv
    setScrutCtxt OccEnv
    env [Alt Id]
    alts) CoreExpr
    scrut

          WUD UsageDetails
    alts_usage (Id
    tagged_bndr, [Alt Id]
    alts')
             = OccEnv
    -> Id
    -> (OccEnv -> WithUsageDetails (Id, [Alt Id]))
    -> WithUsageDetails (Id, [Alt Id])
    forall a.
    OccEnv
    -> Id -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeOne OccEnv
    env Id
    bndr ((OccEnv -> WithUsageDetails (Id, [Alt Id]))
     -> WithUsageDetails (Id, [Alt Id]))
    -> (OccEnv -> WithUsageDetails (Id, [Alt Id]))
    -> WithUsageDetails (Id, [Alt Id])
    forall a b. (a -> b) -> a -> b
    $ \OccEnv
    env ->
               let alt_env :: OccEnv
    alt_env = CoreExpr -> Id -> OccEnv -> OccEnv
    addBndrSwap CoreExpr
    scrut' Id
    bndr (OccEnv -> OccEnv) -> OccEnv -> OccEnv
    forall a b. (a -> b) -> a -> b
    $
                             OccEnv -> OccEnv
    setTailCtxt OccEnv
    env  -- Kill off OccRhs
                   WUD UsageDetails
    alts_usage [Alt Id]
    alts' = OccEnv -> [Alt Id] -> WithUsageDetails [Alt Id]
    do_alts OccEnv
    alt_env [Alt Id]
    alts
                   tagged_bndr :: Id
    tagged_bndr = UsageDetails -> Id -> Id
    tagLamBinder UsageDetails
    alts_usage Id
    bndr
               in UsageDetails -> (Id, [Alt Id]) -> WithUsageDetails (Id, [Alt Id])
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    alts_usage (Id
    tagged_bndr, [Alt Id]
    alts')

          total_usage :: UsageDetails
    total_usage = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    scrut_usage UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    alts_usage
                        -- Alts can have tail calls, but the scrutinee can't

        in UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    total_usage (CoreExpr -> Id -> Type -> [Alt Id] -> CoreExpr
    forall b. Expr b -> b -> Type -> [Alt b] -> Expr b
    Case CoreExpr
    scrut' Id
    tagged_bndr Type
    ty [Alt Id]
    alts')
      where
        do_alts :: OccEnv -> [CoreAlt] -> WithUsageDetails [CoreAlt]
        do_alts :: OccEnv -> [Alt Id] -> WithUsageDetails [Alt Id]
    do_alts OccEnv
    _   []         = UsageDetails -> [Alt Id] -> WithUsageDetails [Alt Id]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    emptyDetails []
        do_alts OccEnv
    env (Alt Id
    alt:[Alt Id]
    alts) = UsageDetails -> [Alt Id] -> WithUsageDetails [Alt Id]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails
    uds1 UsageDetails -> UsageDetails -> UsageDetails
    `orUDs` UsageDetails
    uds2) (Alt Id
    alt'Alt Id -> [Alt Id] -> [Alt Id]
    forall a. a -> [a] -> [a]
    :[Alt Id]
    alts')
          where
            WUD UsageDetails
    uds1 Alt Id
    alt'  = OccEnv -> Alt Id -> WithUsageDetails (Alt Id)
    do_alt  OccEnv
    env Alt Id
    alt
            WUD UsageDetails
    uds2 [Alt Id]
    alts' = OccEnv -> [Alt Id] -> WithUsageDetails [Alt Id]
    do_alts OccEnv
    env [Alt Id]
    alts

        do_alt :: OccEnv -> Alt Id -> WithUsageDetails (Alt Id)
    do_alt !OccEnv
    env (Alt AltCon
    con [Id]
    bndrs CoreExpr
    rhs)
          = OccEnv
    -> [Id]
    -> (OccEnv -> WithUsageDetails (Alt Id))
    -> WithUsageDetails (Alt Id)
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env [Id]
    bndrs ((OccEnv -> WithUsageDetails (Alt Id))
     -> WithUsageDetails (Alt Id))
    -> (OccEnv -> WithUsageDetails (Alt Id))
    -> WithUsageDetails (Alt Id)
    forall a b. (a -> b) -> a -> b
    $ \ OccEnv
    env ->
            let WUD UsageDetails
    rhs_usage CoreExpr
    rhs' = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    rhs
                tagged_bndrs :: [Id]
    tagged_bndrs = UsageDetails -> [Id] -> [Id]
    tagLamBinders UsageDetails
    rhs_usage [Id]
    bndrs
            in                 -- See Note [Binders in case alternatives]
            UsageDetails -> Alt Id -> WithUsageDetails (Alt Id)
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    rhs_usage (AltCon -> [Id] -> CoreExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    tagged_bndrs CoreExpr
    rhs')

    occAnal OccEnv
    env (Let CoreBind
    bind CoreExpr
    body)
      = OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> (OccEnv -> WithUsageDetails CoreExpr)
    -> (CoreProgram -> CoreExpr -> CoreExpr)
    -> WithUsageDetails CoreExpr
    forall r.
    OccEnv
    -> TopLevelFlag
    -> ImpRuleEdges
    -> CoreBind
    -> (OccEnv -> WithUsageDetails r)
    -> (CoreProgram -> r -> r)
    -> WithUsageDetails r
    occAnalBind OccEnv
    env TopLevelFlag
    NotTopLevel ImpRuleEdges
    noImpRuleEdges CoreBind
    bind
                    (\OccEnv
    env -> OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    env CoreExpr
    body) CoreProgram -> CoreExpr -> CoreExpr
    forall b. [Bind b] -> Expr b -> Expr b
    mkLets

    occAnalArgs :: OccEnv -> CoreExpr -> [CoreExpr]
                -> [OneShots]  -- Very commonly empty, notably prior to dmd anal
                -> WithUsageDetails CoreExpr
    -- The `fun` argument is just an accumulating parameter,
    -- the base for building the application we return
    occAnalArgs :: OccEnv
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    occAnalArgs !OccEnv
    env CoreExpr
    fun [CoreExpr]
    args ![[OneShotInfo]]
    one_shots
      = UsageDetails
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    go UsageDetails
    emptyDetails CoreExpr
    fun [CoreExpr]
    args [[OneShotInfo]]
    one_shots
      where
        env_args :: OccEnv
    env_args = OccEncl -> OccEnv -> OccEnv
    setNonTailCtxt OccEncl
    OccVanilla OccEnv
    env

        go :: UsageDetails
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    go UsageDetails
    uds CoreExpr
    fun [] [[OneShotInfo]]
    _ = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    uds CoreExpr
    fun
        go UsageDetails
    uds CoreExpr
    fun (CoreExpr
    arg:[CoreExpr]
    args) [[OneShotInfo]]
    one_shots
          = UsageDetails
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    go (UsageDetails
    uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    arg_uds) (CoreExpr
    fun CoreExpr -> CoreExpr -> CoreExpr
    forall b. Expr b -> Expr b -> Expr b
    `App` CoreExpr
    arg') [CoreExpr]
    args [[OneShotInfo]]
    one_shots'
          where
            !(WUD UsageDetails
    arg_uds CoreExpr
    arg') = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal OccEnv
    arg_env CoreExpr
    arg
            !(OccEnv
    arg_env, [[OneShotInfo]]
    one_shots')
                | CoreExpr -> Bool
    forall {b}. Expr b -> Bool
    isTypeArg CoreExpr
    arg
                = (OccEnv
    env_args, [[OneShotInfo]]
    one_shots)
                | Bool
    otherwise
                = case [[OneShotInfo]]
    one_shots of
                    []                -> (OccEnv
    env_args, []) -- Fast path; one_shots is often empty
                    ([OneShotInfo]
    os : [[OneShotInfo]]
    one_shots') -> ([OneShotInfo] -> OccEnv -> OccEnv
    setOneShots [OneShotInfo]
    os OccEnv
    env_args, [[OneShotInfo]]
    one_shots')

    {-
    Applications are dealt with specially because we want
    the "build hack" to work.

    Note [Arguments of let-bound constructors]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        f x = let y = expensive x in
              let z = (True,y) in
              (case z of {(p,q)->q}, case z of {(p,q)->q})
    We feel free to duplicate the WHNF (True,y), but that means
    that y may be duplicated thereby.

    If we aren't careful we duplicate the (expensive x) call!
    Constructors are rather like lambdas in this way.
    -}

    occAnalApp :: OccEnv
               -> (Expr CoreBndr, [Arg CoreBndr], [CoreTickish])
               -> WithUsageDetails (Expr CoreBndr)
    -- Naked variables (not applied) end up here too
    occAnalApp :: OccEnv
    -> (CoreExpr, [CoreExpr], [CoreTickish])
    -> WithUsageDetails CoreExpr
    occAnalApp !OccEnv
    env (Var Id
    fun, [CoreExpr]
    args, [CoreTickish]
    ticks)
      -- Account for join arity of runRW# continuation
      -- See Note [Simplification of runRW#]
      --
      -- NB: Do not be tempted to make the next (Var fun, args, tick)
      --     equation into an 'otherwise' clause for this equation
      --     The former has a bang-pattern to occ-anal the args, and
      --     we don't want to occ-anal them twice in the runRW# case!
      --     This caused #18296
      | Id
    fun Id -> Unique -> Bool
    forall a. Uniquable a => a -> Unique -> Bool
    `hasKey` Unique
    runRWKey
      , [CoreExpr
    t1, CoreExpr
    t2, CoreExpr
    arg]  <- [CoreExpr]
    args
      , WUD UsageDetails
    usage CoreExpr
    arg' <- JoinPointHood
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    adjustNonRecRhs (JoinArity -> JoinPointHood
    JoinPoint JoinArity
    1) (WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr)
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    forall a b. (a -> b) -> a -> b
    $ OccEnv -> CoreExpr -> WithTailUsageDetails CoreExpr
    occAnalLamTail OccEnv
    env CoreExpr
    arg
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    usage ([CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks (CoreExpr -> CoreExpr) -> CoreExpr -> CoreExpr
    forall a b. (a -> b) -> a -> b
    $ CoreExpr -> [CoreExpr] -> CoreExpr
    forall b. Expr b -> [Expr b] -> Expr b
    mkApps (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    fun) [CoreExpr
    t1, CoreExpr
    t2, CoreExpr
    arg'])

    occAnalApp OccEnv
    env (Var Id
    fun_id, [CoreExpr]
    args, [CoreTickish]
    ticks)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    all_uds ([CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks CoreExpr
    app')
      where
        -- Lots of banged bindings: this is a very heavily bit of code,
        -- so it pays not to make lots of thunks here, all of which
        -- will ultimately be forced.
        !(CoreExpr
    fun', Id
    fun_id')  = OccEnv -> Id -> (CoreExpr, Id)
    lookupBndrSwap OccEnv
    env Id
    fun_id
        !(WUD UsageDetails
    args_uds CoreExpr
    app') = OccEnv
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    occAnalArgs OccEnv
    env CoreExpr
    fun' [CoreExpr]
    args [[OneShotInfo]]
    one_shots

        fun_uds :: UsageDetails
    fun_uds = OccEnv -> Id -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc OccEnv
    env Id
    fun_id' InterestingCxt
    int_cxt JoinArity
    n_args
           -- NB: fun_uds is computed for fun_id', not fun_id
           -- See (BS1) in Note [The binder-swap substitution]

        all_uds :: UsageDetails
    all_uds = UsageDetails
    fun_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    final_args_uds

        !final_args_uds :: UsageDetails
    final_args_uds = UsageDetails -> UsageDetails
    markAllNonTail                              (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                          Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf (OccEnv -> Bool
    isRhsEnv OccEnv
    env Bool -> Bool -> Bool
    && Bool
    is_exp) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
                            -- isRhsEnv: see Note [OccEncl]
                          UsageDetails
    args_uds
           -- We mark the free vars of the argument of a constructor or PAP
           -- as "inside-lambda", if it is the RHS of a let(rec).
           -- This means that nothing gets inlined into a constructor or PAP
           -- argument position, which is what we want.  Typically those
           -- constructor arguments are just variables, or trivial expressions.
           -- We use inside-lam because it's like eta-expanding the PAP.
           --
           -- This is the *whole point* of the isRhsEnv predicate
           -- See Note [Arguments of let-bound constructors]

        !n_val_args :: JoinArity
    n_val_args = [CoreExpr] -> JoinArity
    forall b. [Arg b] -> JoinArity
    valArgCount [CoreExpr]
    args
        !n_args :: JoinArity
    n_args     = [CoreExpr] -> JoinArity
    forall a. [a] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length [CoreExpr]
    args
        !int_cxt :: InterestingCxt
    int_cxt    = case OccEnv -> OccEncl
    occ_encl OccEnv
    env of
                       OccEncl
    OccScrut -> InterestingCxt
    IsInteresting
                       OccEncl
    _other   | JoinArity
    n_val_args JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    0 -> InterestingCxt
    IsInteresting
                                | Bool
    otherwise      -> InterestingCxt
    NotInteresting

        !is_exp :: Bool
    is_exp     = CheapAppFun
    isExpandableApp Id
    fun_id JoinArity
    n_val_args
            -- See Note [CONLIKE pragma] in GHC.Types.Basic
            -- The definition of is_exp should match that in GHC.Core.Opt.Simplify.prepareRhs

        one_shots :: [[OneShotInfo]]
    one_shots  = DmdSig -> JoinArity -> [[OneShotInfo]]
    argsOneShots (Id -> DmdSig
    idDmdSig Id
    fun_id) JoinArity
    guaranteed_val_args
        guaranteed_val_args :: JoinArity
    guaranteed_val_args = JoinArity
    n_val_args JoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    + [OneShotInfo] -> JoinArity
    forall a. [a] -> JoinArity
    forall (t :: * -> *) a. Foldable t => t a -> JoinArity
    length ((OneShotInfo -> Bool) -> [OneShotInfo] -> [OneShotInfo]
    forall a. (a -> Bool) -> [a] -> [a]
    takeWhile OneShotInfo -> Bool
    isOneShotInfo
                                                             (OccEnv -> [OneShotInfo]
    occ_one_shots OccEnv
    env))
            -- See Note [Sources of one-shot information], bullet point A']

    occAnalApp OccEnv
    env (CoreExpr
    fun, [CoreExpr]
    args, [CoreTickish]
    ticks)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (UsageDetails -> UsageDetails
    markAllNonTail (UsageDetails
    fun_uds UsageDetails -> UsageDetails -> UsageDetails
    `andUDs` UsageDetails
    args_uds))
                         ([CoreTickish] -> CoreExpr -> CoreExpr
    mkTicks [CoreTickish]
    ticks CoreExpr
    app')
      where
        !(WUD UsageDetails
    args_uds CoreExpr
    app') = OccEnv
    -> CoreExpr
    -> [CoreExpr]
    -> [[OneShotInfo]]
    -> WithUsageDetails CoreExpr
    occAnalArgs OccEnv
    env CoreExpr
    fun' [CoreExpr]
    args []
        !(WUD UsageDetails
    fun_uds CoreExpr
    fun')  = OccEnv -> CoreExpr -> WithUsageDetails CoreExpr
    occAnal (OccEnv -> [CoreExpr] -> OccEnv
    addAppCtxt OccEnv
    env [CoreExpr]
    args) CoreExpr
    fun
            -- The addAppCtxt is a bit cunning.  One iteration of the simplifier
            -- often leaves behind beta redexes like
            --      (\x y -> e) a1 a2
            -- Here we would like to mark x,y as one-shot, and treat the whole
            -- thing much like a let.  We do this by pushing some OneShotLam items
            -- onto the context stack.

    addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv
    addAppCtxt :: OccEnv -> [CoreExpr] -> OccEnv
    addAppCtxt env :: OccEnv
    env@(OccEnv { occ_one_shots :: OccEnv -> [OneShotInfo]
    occ_one_shots = [OneShotInfo]
    ctxt }) [CoreExpr]
    args
      | JoinArity
    n_val_args JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > JoinArity
    0
      = OccEnv
    env { occ_one_shots = replicate n_val_args OneShotLam ++ ctxt
            , occ_encl      = OccVanilla }
              -- OccVanilla: the function part of the application
              -- is no longer on OccRhs or OccScrut
      | Bool
    otherwise
      = OccEnv
    env
      where
        n_val_args :: JoinArity
    n_val_args = [CoreExpr] -> JoinArity
    forall b. [Arg b] -> JoinArity
    valArgCount [CoreExpr]
    args

    {-
    Note [Sources of one-shot information]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The occurrence analyser obtains one-shot-lambda information from two sources:

    A:  Saturated applications:  eg   f e1 .. en

        In general, given a call (f e1 .. en) we can propagate one-shot info from
        f's strictness signature into e1 .. en, but /only/ if n is enough to
        saturate the strictness signature. A strictness signature like

              f :: C(1,C(1,L))LS

        means that *if f is applied to three arguments* then it will guarantee to
        call its first argument at most once, and to call the result of that at
        most once. But if f has fewer than three arguments, all bets are off; e.g.

              map (f (\x y. expensive) e2) xs

        Here the \x y abstraction may be called many times (once for each element of
        xs) so we should not mark x and y as one-shot. But if it was

              map (f (\x y. expensive) 3 2) xs

        then the first argument of f will be called at most once.

        The one-shot info, derived from f's strictness signature, is
        computed by 'argsOneShots', called in occAnalApp.

    A': Non-obviously saturated applications: eg    build (f (\x y -> expensive))
        where f is as above.

        In this case, f is only manifestly applied to one argument, so it does not
        look saturated. So by the previous point, we should not use its strictness
        signature to learn about the one-shotness of \x y. But in this case we can:
        build is fully applied, so we may use its strictness signature; and from
        that we learn that build calls its argument with two arguments *at most once*.

        So there is really only one call to f, and it will have three arguments. In
        that sense, f is saturated, and we may proceed as described above.

        Hence the computation of 'guaranteed_val_args' in occAnalApp, using
        '(occ_one_shots env)'.  See also #13227, comment:9

    B:  Let-bindings:  eg   let f = \c. let ... in \n -> blah
                            in (build f, build f)

        Propagate one-shot info from the demand-info on 'f' to the
        lambdas in its RHS (which may not be syntactically at the top)

        This information must have come from a previous run of the demand
        analyser.

    Previously, the demand analyser would *also* set the one-shot information, but
    that code was buggy (see #11770), so doing it only in on place, namely here, is
    saner.

    Note [OneShots]
    ~~~~~~~~~~~~~~~
    When analysing an expression, the occ_one_shots argument contains information
    about how the function is being used. The length of the list indicates
    how many arguments will eventually be passed to the analysed expression,
    and the OneShotInfo indicates whether this application is once or multiple times.

    Example:

     Context of f                occ_one_shots when analysing f

     f 1 2                       [OneShot, OneShot]
     map (f 1)                   [OneShot, NoOneShotInfo]
     build f                     [OneShot, OneShot]
     f 1 2 `seq` f 2 1           [NoOneShotInfo, OneShot]

    Note [Binders in case alternatives]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        case x of y { (a,b) -> f y }
    We treat 'a', 'b' as dead, because they don't physically occur in the
    case alternative.  (Indeed, a variable is dead iff it doesn't occur in
    its scope in the output of OccAnal.)  It really helps to know when
    binders are unused.  See esp the call to isDeadBinder in
    Simplify.mkDupableAlt

    In this example, though, the Simplifier will bring 'a' and 'b' back to
    life, because it binds 'y' to (a,b) (imagine got inlined and
    scrutinised y).
    -}

    {-
    ************************************************************************
    *                                                                      *
                        OccEnv
    *                                                                      *
    ************************************************************************
    -}

    data OccEnv
      = OccEnv { OccEnv -> OccEncl
    occ_encl       :: !OccEncl      -- Enclosing context information
               , OccEnv -> [OneShotInfo]
    occ_one_shots  :: !OneShots     -- See Note [OneShots]
               , OccEnv -> Id -> Bool
    occ_unf_act    :: Id -> Bool          -- Which Id unfoldings are active
               , OccEnv -> Activation -> Bool
    occ_rule_act   :: Activation -> Bool  -- Which rules are active
                 -- See Note [Finding rule RHS free vars]

               -- See Note [The binder-swap substitution]
               -- If  x :-> (y, co)  is in the env,
               -- then please replace x by (y |> mco)
               -- Invariant of course: idType x = exprType (y |> mco)
               , OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env  :: !(IdEnv (OutId, MCoercion))
                  -- Domain is Global and Local Ids
                  -- Range is just Local Ids
               , OccEnv -> VarSet
    occ_bs_rng  :: !VarSet
                   -- Vars (TyVars and Ids) free in the range of occ_bs_env

                 -- Usage details of the RHS of in-scope non-recursive join points
                 -- Invariant: no Id maps to an empty OccInfoEnv
                 -- See Note [Occurrence analysis for join points]
               , OccEnv -> JoinPointInfo
    occ_join_points :: !JoinPointInfo
        }

    type JoinPointInfo = IdEnv OccInfoEnv

    -----------------------------
    {- Note [OccEncl]
    ~~~~~~~~~~~~~~~~~
    OccEncl is used to control whether to inline into constructor arguments.

    * OccRhs: consider
         let p = <blah> in
         let x = Just p
         in ...case p of ...

      Here `p` occurs syntactically once, but we want to mark it as InsideLam
      to stop `p` inlining.  We want to leave the x-binding as a constructor
      applied to variables, so that the Simplifier can simplify that inner `case`.

      The OccRhs just tells occAnalApp to mark occurrences in constructor args

    * OccScrut: consider (case x of ...).  Here we want to give `x` OneOcc
      with "interesting context" field int_cxt = True.  The OccScrut tells
      occAnalApp (which deals with lone variables too) when to set this field
      to True.
    -}

    data OccEncl -- See Note [OccEncl]
      = OccRhs         -- RHS of let(rec), albeit perhaps inside a type lambda
      | OccScrut       -- Scrutintee of a case
      | OccVanilla     -- Everything else

    instance Outputable OccEncl where
      ppr :: OccEncl -> SDoc
    ppr OccEncl
    OccRhs     = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "occRhs"
      ppr OccEncl
    OccScrut   = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "occScrut"
      ppr OccEncl
    OccVanilla = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "occVanilla"

    -- See Note [OneShots]
    type OneShots = [OneShotInfo]

    initOccEnv :: OccEnv
    initOccEnv :: OccEnv
    initOccEnv
      = OccEnv { occ_encl :: OccEncl
    occ_encl      = OccEncl
    OccVanilla
               , occ_one_shots :: [OneShotInfo]
    occ_one_shots = []

                     -- To be conservative, we say that all
                     -- inlines and rules are active
               , occ_unf_act :: Id -> Bool
    occ_unf_act   = \Id
    _ -> Bool
    True
               , occ_rule_act :: Activation -> Bool
    occ_rule_act  = \Activation
    _ -> Bool
    True

               , occ_join_points :: JoinPointInfo
    occ_join_points = JoinPointInfo
    forall a. VarEnv a
    emptyVarEnv
               , occ_bs_env :: IdEnv (Id, MCoercion)
    occ_bs_env = IdEnv (Id, MCoercion)
    forall a. VarEnv a
    emptyVarEnv
               , occ_bs_rng :: VarSet
    occ_bs_rng = VarSet
    emptyVarSet }

    noBinderSwaps :: OccEnv -> Bool
    noBinderSwaps :: OccEnv -> Bool
    noBinderSwaps (OccEnv { occ_bs_env :: OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env = IdEnv (Id, MCoercion)
    bs_env }) = IdEnv (Id, MCoercion) -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv IdEnv (Id, MCoercion)
    bs_env

    setScrutCtxt :: OccEnv -> [CoreAlt] -> OccEnv
    setScrutCtxt :: OccEnv -> [Alt Id] -> OccEnv
    setScrutCtxt !OccEnv
    env [Alt Id]
    alts
      = OccEncl -> OccEnv -> OccEnv
    setNonTailCtxt OccEncl
    encl OccEnv
    env
      where
        encl :: OccEncl
    encl | Bool
    interesting_alts = OccEncl
    OccScrut
             | Bool
    otherwise        = OccEncl
    OccVanilla

        interesting_alts :: Bool
    interesting_alts = case [Alt Id]
    alts of
                             []    -> Bool
    False
                             [Alt Id
    alt] -> Bool -> Bool
    not (Alt Id -> Bool
    forall b. Alt b -> Bool
    isDefaultAlt Alt Id
    alt)
                             [Alt Id]
    _     -> Bool
    True
         -- 'interesting_alts' is True if the case has at least one
         -- non-default alternative.  That in turn influences
         -- pre/postInlineUnconditionally.  Grep for "occ_int_cxt"!

    {- Note [The OccEnv for a right hand side]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    How do we create the OccEnv for a RHS (in mkRhsOccEnv)?

    For a non-join point binding, x = rhs

      * occ_encl: set to OccRhs; but see `mkNonRecRhsCtxt` for wrinkles

      * occ_join_points: zap them!

      * occ_one_shots: initialise from the idDemandInfo;
        see Note [Sources of one-shot information]

    For a join point binding,  j x = rhs

      * occ_encl: Consider
           x = e
           join j = Just x
        We want to inline x into j right away, so we don't want to give the join point
        a OccRhs (#14137); we want OccVanilla.  It's not a huge deal, because the
        FloatIn pass knows to float into join point RHSs; and the simplifier does not
        float things out of join point RHSs.  But it's a simple, cheap thing to do.

      * occ_join_points: no need to zap.

      * occ_one_shots: we start with one-shot-info from the context, which indeed
        applies to the /body/ of the join point, after walking past the binders.
        So we add to the front a OneShotInfo for each value-binder of the join
        point: see `extendOneShotsForJoinPoint`. (Failing to account for the join-point
        binders caused #25096.)

        For the join point binders themselves, of a /non-recursive/ join point,
        we make the binder a OneShotLam.  Again see `extendOneShotsForJoinPoint`.

        These one-shot infos then get attached to the binder by `occAnalLamTail`.
    -}

    setNonTailCtxt :: OccEncl -> OccEnv -> OccEnv
    setNonTailCtxt :: OccEncl -> OccEnv -> OccEnv
    setNonTailCtxt OccEncl
    ctxt !OccEnv
    env
      = OccEnv
    env { occ_encl        = ctxt
            , occ_one_shots   = []
            , occ_join_points = zapJoinPointInfo (occ_join_points env) }

    setTailCtxt :: OccEnv -> OccEnv
    setTailCtxt :: OccEnv -> OccEnv
    setTailCtxt !OccEnv
    env = OccEnv
    env { occ_encl = OccVanilla }
        -- Preserve occ_one_shots, occ_join points
        -- Do not use OccRhs for the RHS of a join point (which is a tail ctxt):

    mkRhsOccEnv :: OccEnv -> RecFlag -> OccEncl -> JoinPointHood -> Id -> CoreExpr -> OccEnv
    -- See Note [The OccEnv for a right hand side]
    -- For a join point:
    --   - Keep occ_one_shots, occ_joinPoints from the context
    --   - But push enough OneShotInfo onto occ_one_shots to account
    --     for the join-point value binders
    --   - Set occ_encl to OccVanilla
    -- For non-join points
    --   - Zap occ_one_shots and occ_join_points
    --   - Set occ_encl to specified OccEncl
    mkRhsOccEnv :: OccEnv
    -> RecFlag -> OccEncl -> JoinPointHood -> Id -> CoreExpr -> OccEnv
    mkRhsOccEnv env :: OccEnv
    env@(OccEnv { occ_one_shots :: OccEnv -> [OneShotInfo]
    occ_one_shots = [OneShotInfo]
    ctxt_one_shots, occ_join_points :: OccEnv -> JoinPointInfo
    occ_join_points = JoinPointInfo
    ctxt_join_points })
                RecFlag
    is_rec OccEncl
    encl JoinPointHood
    jp_hood Id
    bndr CoreExpr
    rhs
      | JoinPoint JoinArity
    join_arity <- JoinPointHood
    jp_hood
      = OccEnv
    env { occ_encl        = OccVanilla
            , occ_one_shots   = extendOneShotsForJoinPoint is_rec join_arity rhs ctxt_one_shots
            , occ_join_points = ctxt_join_points }

      | Bool
    otherwise
      = OccEnv
    env { occ_encl        = encl
            , occ_one_shots   = argOneShots (idDemandInfo bndr)
                                -- argOneShots: see Note [Sources of one-shot information]
            , occ_join_points = zapJoinPointInfo ctxt_join_points }

    zapJoinPointInfo :: JoinPointInfo -> JoinPointInfo
    -- (zapJoinPointInfo jp_info) basically just returns emptyVarEnv (hence zapped).
    -- See (W3) of Note [Occurrence analysis for join points]
    --
    -- Zapping improves efficiency, slightly, if you accidentally introduce a bug,
    -- in which you zap [jx :-> uds] and then find an occurrence of jx anyway, you
    -- might lose those uds, and that might mean we don't record all occurrencs, and
    -- that means we duplicate a redex....  a very nasty bug (which I encountered!).
    -- Hence this DEBUG code which doesn't remove jx from the envt; it just gives it
    -- emptyDetails, which in turn causes a panic in mkOneOcc. That will catch this
    -- bug before it does any damage.
    #ifdef DEBUG
    zapJoinPointInfo jp_info = mapVarEnv (\ _ -> emptyVarEnv) jp_info
    #else
    zapJoinPointInfo :: JoinPointInfo -> JoinPointInfo
    zapJoinPointInfo JoinPointInfo
    _       = JoinPointInfo
    forall a. VarEnv a
    emptyVarEnv
    #endif

    extendOneShotsForJoinPoint
      :: RecFlag -> JoinArity -> CoreExpr
      -> [OneShotInfo] -> [OneShotInfo]
    -- Push enough OneShortInfos on the front of ctxt_one_shots
    -- to account for the value lambdas of the join point
    extendOneShotsForJoinPoint :: RecFlag -> JoinArity -> CoreExpr -> [OneShotInfo] -> [OneShotInfo]
    extendOneShotsForJoinPoint RecFlag
    is_rec JoinArity
    join_arity CoreExpr
    rhs [OneShotInfo]
    ctxt_one_shots
      = JoinArity -> CoreExpr -> [OneShotInfo]
    go JoinArity
    join_arity CoreExpr
    rhs
      where
        -- For a /non-recursive/ join point we can mark all
        -- its join-lambda as one-shot; and it's a good idea to do so
        -- But not so for recursive ones
        os :: OneShotInfo
    os = case RecFlag
    is_rec of
               RecFlag
    NonRecursive -> OneShotInfo
    OneShotLam
               RecFlag
    Recursive    -> OneShotInfo
    NoOneShotInfo

        go :: JoinArity -> CoreExpr -> [OneShotInfo]
    go JoinArity
    0 CoreExpr
    _        = [OneShotInfo]
    ctxt_one_shots
        go JoinArity
    n (Lam Id
    b CoreExpr
    rhs)
          | Id -> Bool
    isId Id
    b    = OneShotInfo
    os OneShotInfo -> [OneShotInfo] -> [OneShotInfo]
    forall a. a -> [a] -> [a]
    : JoinArity -> CoreExpr -> [OneShotInfo]
    go (JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    -JoinArity
    1) CoreExpr
    rhs
          | Bool
    otherwise =      JoinArity -> CoreExpr -> [OneShotInfo]
    go (JoinArity
    nJoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    -JoinArity
    1) CoreExpr
    rhs
        go JoinArity
    _ CoreExpr
    _        = []  -- Not enough lambdas.  This can legitimately happen.
                            -- e.g.    let j = case ... in j True
                            -- This will become an arity-1 join point after the
                            -- simplifier has eta-expanded it; but it may not have
                            -- enough lambdas /yet/. (Lint checks that JoinIds do
                            -- have enough lambdas.)

    setOneShots :: OneShots -> OccEnv -> OccEnv
    setOneShots :: [OneShotInfo] -> OccEnv -> OccEnv
    setOneShots [OneShotInfo]
    os !OccEnv
    env
      | [OneShotInfo] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [OneShotInfo]
    os   = OccEnv
    env  -- Fast path for common case
      | Bool
    otherwise = OccEnv
    env { occ_one_shots = os }

    isRhsEnv :: OccEnv -> Bool
    isRhsEnv :: OccEnv -> Bool
    isRhsEnv (OccEnv { occ_encl :: OccEnv -> OccEncl
    occ_encl = OccEncl
    cxt }) = case OccEncl
    cxt of
                                              OccEncl
    OccRhs -> Bool
    True
                                              OccEncl
    _      -> Bool
    False

    addInScopeList :: OccEnv -> [Var]
                   -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    {-# INLINE addInScopeList #-}
    addInScopeList :: forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeList OccEnv
    env [Id]
    bndrs OccEnv -> WithUsageDetails a
    thing_inside
     | [Id] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    bndrs = OccEnv -> WithUsageDetails a
    thing_inside OccEnv
    env  -- E.g. nullary constructors in a `case`
     | Bool
    otherwise  = OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScope OccEnv
    env [Id]
    bndrs OccEnv -> WithUsageDetails a
    thing_inside

    addInScopeOne :: OccEnv -> Id
                   -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    {-# INLINE addInScopeOne #-}
    addInScopeOne :: forall a.
    OccEnv
    -> Id -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScopeOne OccEnv
    env Id
    bndr = OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScope OccEnv
    env [Id
    bndr]

    addInScope :: OccEnv -> [Var]
               -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    {-# INLINE addInScope #-}
    -- This function is called a lot, so we want to inline the fast path
    -- so we don't have to allocate thing_inside and call it
    -- The bndrs must include TyVars as well as Ids, because of
    --     (BS3) in Note [Binder swap]
    -- We do not assume that the bndrs are in scope order; in fact the
    -- call in occ_anal_lam_tail gives them to addInScope in /reverse/ order

    -- Fast path when the is no environment-munging to do
    -- This is rather common: notably at top level, but nested too
    addInScope :: forall a.
    OccEnv
    -> [Id] -> (OccEnv -> WithUsageDetails a) -> WithUsageDetails a
    addInScope OccEnv
    env [Id]
    bndrs OccEnv -> WithUsageDetails a
    thing_inside
      | IdEnv (Id, MCoercion) -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv (OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env OccEnv
    env)
      , JoinPointInfo -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv (OccEnv -> JoinPointInfo
    occ_join_points OccEnv
    env)
      , WUD UsageDetails
    uds a
    res <- OccEnv -> WithUsageDetails a
    thing_inside OccEnv
    env
      = UsageDetails -> a -> WithUsageDetails a
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD ([Id] -> UsageDetails -> UsageDetails
    delBndrsFromUDs [Id]
    bndrs UsageDetails
    uds) a
    res

    addInScope OccEnv
    env [Id]
    bndrs OccEnv -> WithUsageDetails a
    thing_inside
      = UsageDetails -> a -> WithUsageDetails a
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    uds' a
    res
      where
        bndr_set :: VarSet
    bndr_set           = [Id] -> VarSet
    mkVarSet [Id]
    bndrs
        !(OccEnv
    env', JoinPointInfo
    bad_joins) = OccEnv -> VarSet -> (OccEnv, JoinPointInfo)
    preprocess_env OccEnv
    env VarSet
    bndr_set
        !(WUD UsageDetails
    uds a
    res)     = OccEnv -> WithUsageDetails a
    thing_inside OccEnv
    env'
        uds' :: UsageDetails
    uds'               = [Id] -> JoinPointInfo -> UsageDetails -> UsageDetails
    postprocess_uds [Id]
    bndrs JoinPointInfo
    bad_joins UsageDetails
    uds

    preprocess_env :: OccEnv -> VarSet -> (OccEnv, JoinPointInfo)
    preprocess_env :: OccEnv -> VarSet -> (OccEnv, JoinPointInfo)
    preprocess_env env :: OccEnv
    env@(OccEnv { occ_join_points :: OccEnv -> JoinPointInfo
    occ_join_points = JoinPointInfo
    join_points
                               , occ_bs_rng :: OccEnv -> VarSet
    occ_bs_rng = VarSet
    bs_rng_vars })
                   VarSet
    bndr_set
      | Bool
    bad_joins = (OccEnv -> OccEnv
    drop_shadowed_swaps (OccEnv -> OccEnv
    drop_shadowed_joins OccEnv
    env), JoinPointInfo
    join_points)
      | Bool
    otherwise = (OccEnv -> OccEnv
    drop_shadowed_swaps OccEnv
    env,                       JoinPointInfo
    forall a. VarEnv a
    emptyVarEnv)
      where
        drop_shadowed_swaps :: OccEnv -> OccEnv
        -- See Note [The binder-swap substitution] (BS3)
        drop_shadowed_swaps :: OccEnv -> OccEnv
    drop_shadowed_swaps env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env = IdEnv (Id, MCoercion)
    swap_env })
          | IdEnv (Id, MCoercion) -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv IdEnv (Id, MCoercion)
    swap_env
          = OccEnv
    env
          | VarSet
    bs_rng_vars VarSet -> VarSet -> Bool
    `intersectsVarSet` VarSet
    bndr_set
          = OccEnv
    env { occ_bs_env = emptyVarEnv, occ_bs_rng = emptyVarSet }
          | Bool
    otherwise
          = OccEnv
    env { occ_bs_env = swap_env `minusUFM` bndr_fm }

        drop_shadowed_joins :: OccEnv -> OccEnv
        -- See Note [Occurrence analysis for join points] wrinkle2 (W1) and (W2)
        drop_shadowed_joins :: OccEnv -> OccEnv
    drop_shadowed_joins OccEnv
    env = OccEnv
    env { occ_join_points = emptyVarEnv }

        -- bad_joins is true if it would be wrong to push occ_join_points inwards
        --  (a) `bndrs` includes any of the occ_join_points
        --  (b) `bndrs` includes any variables free in the RHSs of occ_join_points
        bad_joins :: Bool
        bad_joins :: Bool
    bad_joins = (Unique -> VarEnv LocalOcc -> Bool -> Bool)
    -> Bool -> JoinPointInfo -> Bool
    forall a r. (Unique -> a -> r -> r) -> r -> VarEnv a -> r
    nonDetStrictFoldVarEnv_Directly Unique -> VarEnv LocalOcc -> Bool -> Bool
    is_bad Bool
    False JoinPointInfo
    join_points

        bndr_fm :: UniqFM Var Var
        bndr_fm :: VarEnv Id
    bndr_fm = VarSet -> VarEnv Id
    forall a. UniqSet a -> UniqFM a a
    getUniqSet VarSet
    bndr_set

        is_bad :: Unique -> OccInfoEnv -> Bool -> Bool
        is_bad :: Unique -> VarEnv LocalOcc -> Bool -> Bool
    is_bad Unique
    uniq VarEnv LocalOcc
    join_uds Bool
    rest
          = Unique
    uniq Unique -> VarSet -> Bool
    forall a. Unique -> UniqSet a -> Bool
    `elemUniqSet_Directly` VarSet
    bndr_set Bool -> Bool -> Bool
    ||
            Bool -> Bool
    not (VarEnv Id
    bndr_fm VarEnv Id -> VarEnv LocalOcc -> Bool
    forall {k} (key :: k) elt1 elt2.
    UniqFM key elt1 -> UniqFM key elt2 -> Bool
    `disjointUFM` VarEnv LocalOcc
    join_uds) Bool -> Bool -> Bool
    ||
            Bool
    rest

    postprocess_uds :: [Var] -> JoinPointInfo -> UsageDetails -> UsageDetails
    postprocess_uds :: [Id] -> JoinPointInfo -> UsageDetails -> UsageDetails
    postprocess_uds [Id]
    bndrs JoinPointInfo
    bad_joins UsageDetails
    uds
      = UsageDetails -> UsageDetails
    add_bad_joins ([Id] -> UsageDetails -> UsageDetails
    delBndrsFromUDs [Id]
    bndrs UsageDetails
    uds)
      where
        add_bad_joins :: UsageDetails -> UsageDetails
        -- Add usage info for occ_join_points that we cannot push inwards
        -- because of shadowing
        -- See Note [Occurrence analysis for join points] wrinkle (W2)
        add_bad_joins :: UsageDetails -> UsageDetails
    add_bad_joins UsageDetails
    uds
           | JoinPointInfo -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv JoinPointInfo
    bad_joins = UsageDetails
    uds
           | Bool
    otherwise               = (VarEnv LocalOcc -> VarEnv LocalOcc)
    -> UsageDetails -> UsageDetails
    modifyUDEnv VarEnv LocalOcc -> VarEnv LocalOcc
    extend_with_bad_joins UsageDetails
    uds

        extend_with_bad_joins :: OccInfoEnv -> OccInfoEnv
        extend_with_bad_joins :: VarEnv LocalOcc -> VarEnv LocalOcc
    extend_with_bad_joins VarEnv LocalOcc
    env
           = (Unique -> VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc)
    -> VarEnv LocalOcc -> JoinPointInfo -> VarEnv LocalOcc
    forall {k} elt a (key :: k).
    (Unique -> elt -> a -> a) -> a -> UniqFM key elt -> a
    nonDetStrictFoldUFM_Directly Unique -> VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    add_bad_join VarEnv LocalOcc
    env JoinPointInfo
    bad_joins

        add_bad_join :: Unique -> OccInfoEnv -> OccInfoEnv -> OccInfoEnv
        -- Behave like `andUDs` when adding in the bad_joins
        add_bad_join :: Unique -> VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    add_bad_join Unique
    uniq VarEnv LocalOcc
    join_env VarEnv LocalOcc
    env
          | Unique
    uniq Unique -> VarEnv LocalOcc -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` VarEnv LocalOcc
    env = (LocalOcc -> LocalOcc -> LocalOcc)
    -> VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall a. (a -> a -> a) -> VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv_C LocalOcc -> LocalOcc -> LocalOcc
    andLocalOcc VarEnv LocalOcc
    env VarEnv LocalOcc
    join_env
          | Bool
    otherwise                  = VarEnv LocalOcc
    env

    addJoinPoint :: OccEnv -> Id -> UsageDetails -> OccEnv
    addJoinPoint :: OccEnv -> Id -> UsageDetails -> OccEnv
    addJoinPoint OccEnv
    env Id
    bndr UsageDetails
    rhs_uds
      | VarEnv LocalOcc -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv LocalOcc
    zeroed_form
      = OccEnv
    env
      | Bool
    otherwise
      = OccEnv
    env { occ_join_points = extendVarEnv (occ_join_points env) bndr zeroed_form }
      where
        zeroed_form :: VarEnv LocalOcc
    zeroed_form = UsageDetails -> VarEnv LocalOcc
    mkZeroedForm UsageDetails
    rhs_uds

    mkZeroedForm :: UsageDetails -> OccInfoEnv
    -- See Note [Occurrence analysis for join points] for "zeroed form"
    mkZeroedForm :: UsageDetails -> VarEnv LocalOcc
    mkZeroedForm (UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    rhs_occs })
      = (LocalOcc -> Maybe LocalOcc) -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall {k} elt1 elt2 (key :: k).
    (elt1 -> Maybe elt2) -> UniqFM key elt1 -> UniqFM key elt2
    mapMaybeUFM LocalOcc -> Maybe LocalOcc
    do_one VarEnv LocalOcc
    rhs_occs
      where
        do_one :: LocalOcc -> Maybe LocalOcc
        do_one :: LocalOcc -> Maybe LocalOcc
    do_one (ManyOccL {})    = Maybe LocalOcc
    forall a. Maybe a
    Nothing
        do_one occ :: LocalOcc
    occ@(OneOccL {}) = LocalOcc -> Maybe LocalOcc
    forall a. a -> Maybe a
    Just (LocalOcc
    occ { lo_n_br = 0 })

    --------------------
    transClosureFV :: VarEnv VarSet -> VarEnv VarSet
    -- If (f,g), (g,h) are in the input, then (f,h) is in the output
    --                                   as well as (f,g), (g,h)
    transClosureFV :: VarEnv VarSet -> VarEnv VarSet
    transClosureFV VarEnv VarSet
    env
      | Bool
    no_change = VarEnv VarSet
    env
      | Bool
    otherwise = VarEnv VarSet -> VarEnv VarSet
    transClosureFV ([(Unique, VarSet)] -> VarEnv VarSet
    forall {k} elt (key :: k). [(Unique, elt)] -> UniqFM key elt
    listToUFM_Directly [(Unique, VarSet)]
    new_fv_list)
      where
        (Bool
    no_change, [(Unique, VarSet)]
    new_fv_list) = (Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet)))
    -> Bool -> [(Unique, VarSet)] -> (Bool, [(Unique, VarSet)])
    forall (t :: * -> *) s a b.
    Traversable t =>
    (s -> a -> (s, b)) -> s -> t a -> (s, t b)
    mapAccumL Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet))
    bump Bool
    True (VarEnv VarSet -> [(Unique, VarSet)]
    forall {k} (key :: k) elt. UniqFM key elt -> [(Unique, elt)]
    nonDetUFMToList VarEnv VarSet
    env)
          -- It's OK to use nonDetUFMToList here because we'll forget the
          -- ordering by creating a new set with listToUFM
        bump :: Bool -> (Unique, VarSet) -> (Bool, (Unique, VarSet))
    bump Bool
    no_change (Unique
    b,VarSet
    fvs)
          | Bool
    no_change_here = (Bool
    no_change, (Unique
    b,VarSet
    fvs))
          | Bool
    otherwise      = (Bool
    False,     (Unique
    b,VarSet
    new_fvs))
          where
            (VarSet
    new_fvs, Bool
    no_change_here) = VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    fvs

    -------------
    extendFvs_ :: VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ :: VarEnv VarSet -> VarSet -> VarSet
    extendFvs_ VarEnv VarSet
    env VarSet
    s = (VarSet, Bool) -> VarSet
    forall a b. (a, b) -> a
    fst (VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    s)   -- Discard the Bool flag

    extendFvs :: VarEnv VarSet -> VarSet -> (VarSet, Bool)
    -- (extendFVs env s) returns
    --     (s `union` env(s), env(s) `subset` s)
    extendFvs :: VarEnv VarSet -> VarSet -> (VarSet, Bool)
    extendFvs VarEnv VarSet
    env VarSet
    s
      | VarEnv VarSet -> Bool
    forall {k} (key :: k) elt. UniqFM key elt -> Bool
    isNullUFM VarEnv VarSet
    env
      = (VarSet
    s, Bool
    True)
      | Bool
    otherwise
      = (VarSet
    s VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    extras, VarSet
    extras VarSet -> VarSet -> Bool
    `subVarSet` VarSet
    s)
      where
        extras :: VarSet    -- env(s)
        extras :: VarSet
    extras = (VarSet -> VarSet -> VarSet) -> VarSet -> VarEnv VarSet -> VarSet
    forall {k} elt a (key :: k).
    (elt -> a -> a) -> a -> UniqFM key elt -> a
    nonDetStrictFoldUFM VarSet -> VarSet -> VarSet
    unionVarSet VarSet
    emptyVarSet (VarEnv VarSet -> VarSet) -> VarEnv VarSet -> VarSet
    forall a b. (a -> b) -> a -> b
    $
          -- It's OK to use nonDetStrictFoldUFM here because unionVarSet commutes
                 (VarSet -> Id -> VarSet)
    -> VarEnv VarSet -> VarEnv Id -> VarEnv VarSet
    forall {k} elt1 elt2 elt3 (key :: k).
    (elt1 -> elt2 -> elt3)
    -> UniqFM key elt1 -> UniqFM key elt2 -> UniqFM key elt3
    intersectUFM_C (\VarSet
    x Id
    _ -> VarSet
    x) VarEnv VarSet
    env (VarSet -> VarEnv Id
    forall a. UniqSet a -> UniqFM a a
    getUniqSet VarSet
    s)

    {-
    ************************************************************************
    *                                                                      *
                        Binder swap
    *                                                                      *
    ************************************************************************

    Note [Binder swap]
    ~~~~~~~~~~~~~~~~~~
    The "binder swap" transformation swaps occurrence of the
    scrutinee of a case for occurrences of the case-binder:

     (1)  case x of b { pi -> ri }
             ==>
          case x of b { pi -> ri[b/x] }

     (2)  case (x |> co) of b { pi -> ri }
            ==>
          case (x |> co) of b { pi -> ri[b |> sym co/x] }

    The substitution ri[b/x] etc is done by the occurrence analyser.
    See Note [The binder-swap substitution].

    There are two reasons for making this swap:

    (A) It reduces the number of occurrences of the scrutinee, x.
        That in turn might reduce its occurrences to one, so we
        can inline it and save an allocation.  E.g.
          let x = factorial y in case x of b { I# v -> ...x... }
        If we replace 'x' by 'b' in the alternative we get
          let x = factorial y in case x of b { I# v -> ...b... }
        and now we can inline 'x', thus
          case (factorial y) of b { I# v -> ...b... }

    (B) The case-binder b has unfolding information; in the
        example above we know that b = I# v. That in turn allows
        nested cases to simplify.  Consider
           case x of b { I# v ->
           ...(case x of b2 { I# v2 -> rhs })...
        If we replace 'x' by 'b' in the alternative we get
           case x of b { I# v ->
           ...(case b of b2 { I# v2 -> rhs })...
        and now it is trivial to simplify the inner case:
           case x of b { I# v ->
           ...(let b2 = b in rhs)...

        The same can happen even if the scrutinee is a variable
        with a cast: see Note [Case of cast]

    The reason for doing these transformations /here in the occurrence
    analyser/ is because it allows us to adjust the OccInfo for 'x' and
    'b' as we go.

      * Suppose the only occurrences of 'x' are the scrutinee and in the
        ri; then this transformation makes it occur just once, and hence
        get inlined right away.

      * If instead the Simplifier replaces occurrences of x with
        occurrences of b, that will mess up b's occurrence info. That in
        turn might have consequences.

    There is a danger though.  Consider
          let v = x +# y
          in case (f v) of w -> ...v...v...
    And suppose that (f v) expands to just v.  Then we'd like to
    use 'w' instead of 'v' in the alternative.  But it may be too
    late; we may have substituted the (cheap) x+#y for v in the
    same simplifier pass that reduced (f v) to v.

    I think this is just too bad.  CSE will recover some of it.

    Note [The binder-swap substitution]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The binder-swap is implemented by the occ_bs_env field of OccEnv.
    There are two main pieces:

    * Given    case x |> co of b { alts }
      we add [x :-> (b, sym co)] to the occ_bs_env environment; this is
      done by addBndrSwap.

    * Then, at an occurrence of a variable, we look up in the occ_bs_env
      to perform the swap. This is done by lookupBndrSwap.

    Some tricky corners:

    (BS1) We do the substitution before gathering occurrence info. So in
          the above example, an occurrence of x turns into an occurrence
          of b, and that's what we gather in the UsageDetails.  It's as
          if the binder-swap occurred before occurrence analysis. See
          the computation of fun_uds in occAnalApp.

    (BS2) When doing a lookup in occ_bs_env, we may need to iterate,
          as you can see implemented in lookupBndrSwap.  Why?
          Consider   case x of a { 1# -> e1; DEFAULT ->
                     case x of b { 2# -> e2; DEFAULT ->
                     case x of c { 3# -> e3; DEFAULT -> ..x..a..b.. }}}
          At the first case addBndrSwap will extend occ_bs_env with
              [x :-> a]
          At the second case we occ-anal the scrutinee 'x', which looks up
            'x in occ_bs_env, returning 'a', as it should.
          Then addBndrSwap will add [a :-> b] to occ_bs_env, yielding
             occ_bs_env = [x :-> a, a :-> b]
          At the third case we'll again look up 'x' which returns 'a'.
          But we don't want to stop the lookup there, else we'll end up with
                     case x of a { 1# -> e1; DEFAULT ->
                     case a of b { 2# -> e2; DEFAULT ->
                     case a of c { 3# -> e3; DEFAULT -> ..a..b..c.. }}}
          Instead, we want iterate the lookup in addBndrSwap, to give
                     case x of a { 1# -> e1; DEFAULT ->
                     case a of b { 2# -> e2; DEFAULT ->
                     case b of c { 3# -> e3; DEFAULT -> ..c..c..c.. }}}
          This makes a particular difference for case-merge, which works
          only if the scrutinee is the case-binder of the immediately enclosing
          case (Note [Merge Nested Cases] in GHC.Core.Opt.Simplify.Utils
          See #19581 for the bug report that showed this up.

    (BS3) We need care when shadowing.  Suppose [x :-> b] is in occ_bs_env,
          and we encounter:
             (i) \x. blah
                 Here we want to delete the x-binding from occ_bs_env

             (ii) \b. blah
                  This is harder: we really want to delete all bindings that
                  have 'b' free in the range.  That is a bit tiresome to implement,
                  so we compromise.  We keep occ_bs_rng, which is the set of
                  free vars of rng(occc_bs_env).  If a binder shadows any of these
                  variables, we discard all of occ_bs_env.  Safe, if a bit
                  brutal.  NB, however: the simplifer de-shadows the code, so the
                  next time around this won't happen.

          These checks are implemented in addInScope.
          (i) is needed only for Ids, but (ii) is needed for tyvars too (#22623)
          because if occ_bs_env has [x :-> ...a...] where `a` is a tyvar, we
          must not replace `x` by `...a...` under /\a. ...x..., or similarly
          under a case pattern match that binds `a`.

          An alternative would be for the occurrence analyser to do cloning as
          it goes.  In principle it could do so, but it'd make it a bit more
          complicated and there is no great benefit. The simplifer uses
          cloning to get a no-shadowing situation, the care-when-shadowing
          behaviour above isn't needed for long.

    (BS4) The domain of occ_bs_env can include GlobaIds.  Eg
             case M.foo of b { alts }
          We extend occ_bs_env with [M.foo :-> b].  That's fine.

    (BS5) We have to apply the occ_bs_env substitution uniformly,
          including to (local) rules and unfoldings.

    (BS6) We must be very careful with dictionaries.
          See Note [Care with binder-swap on dictionaries]

    Note [Case of cast]
    ~~~~~~~~~~~~~~~~~~~
    Consider        case (x `cast` co) of b { I# ->
                    ... (case (x `cast` co) of {...}) ...
    We'd like to eliminate the inner case.  That is the motivation for
    equation (2) in Note [Binder swap].  When we get to the inner case, we
    inline x, cancel the casts, and away we go.

    Note [Care with binder-swap on dictionaries]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    This Note explains why we need isDictId in scrutBinderSwap_maybe.
    Consider this tricky example (#21229, #21470):

      class Sing (b :: Bool) where sing :: Bool
      instance Sing 'True  where sing = True
      instance Sing 'False where sing = False

      f :: forall a. Sing a => blah

      h = \ @(a :: Bool) ($dSing :: Sing a)
          let the_co =  Main.N:Sing[0] <a> :: Sing a ~R# Bool
          case ($dSing |> the_co) of wild
            True  -> f @'True (True |> sym the_co)
            False -> f @a     dSing

    Now do a binder-swap on the case-expression:

      h = \ @(a :: Bool) ($dSing :: Sing a)
          let the_co =  Main.N:Sing[0] <a> :: Sing a ~R# Bool
          case ($dSing |> the_co) of wild
            True  -> f @'True (True |> sym the_co)
            False -> f @a     (wild |> sym the_co)

    And now substitute `False` for `wild` (since wild=False in the False branch):

      h = \ @(a :: Bool) ($dSing :: Sing a)
          let the_co =  Main.N:Sing[0] <a> :: Sing a ~R# Bool
          case ($dSing |> the_co) of wild
            True  -> f @'True (True  |> sym the_co)
            False -> f @a     (False |> sym the_co)

    And now we have a problem.  The specialiser will specialise (f @a d)a (for all
    vtypes a and dictionaries d!!) with the dictionary (False |> sym the_co), using
    Note [Specialising polymorphic dictionaries] in GHC.Core.Opt.Specialise.

    The real problem is the binder-swap.  It swaps a dictionary variable $dSing
    (of kind Constraint) for a term variable wild (of kind Type).  And that is
    dangerous: a dictionary is a /singleton/ type whereas a general term variable is
    not.  In this particular example, Bool is most certainly not a singleton type!

    Conclusion:
      for a /dictionary variable/ do not perform
      the clever cast version of the binder-swap

    Hence the subtle isDictId in scrutBinderSwap_maybe.

    Note [Zap case binders in proxy bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    From the original
         case x of cb(dead) { p -> ...x... }
    we will get
         case x of cb(live) { p -> ...cb... }

    Core Lint never expects to find an *occurrence* of an Id marked
    as Dead, so we must zap the OccInfo on cb before making the
    binding x = cb.  See #5028.

    NB: the OccInfo on /occurrences/ really doesn't matter much; the simplifier
    doesn't use it. So this is only to satisfy the perhaps-over-picky Lint.

    -}

    addBndrSwap :: OutExpr -> Id -> OccEnv -> OccEnv
    -- See Note [The binder-swap substitution]
    addBndrSwap :: CoreExpr -> Id -> OccEnv -> OccEnv
    addBndrSwap CoreExpr
    scrut Id
    case_bndr
                env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env = IdEnv (Id, MCoercion)
    swap_env, occ_bs_rng :: OccEnv -> VarSet
    occ_bs_rng = VarSet
    rng_vars })
      | Just (Id
    scrut_var, MCoercion
    mco) <- CoreExpr -> Maybe (Id, MCoercion)
    scrutBinderSwap_maybe CoreExpr
    scrut
      , Id
    scrut_var Id -> Id -> Bool
    forall a. Eq a => a -> a -> Bool
    /= Id
    case_bndr
          -- Consider: case x of x { ... }
          -- Do not add [x :-> x] to occ_bs_env, else lookupBndrSwap will loop
      = OccEnv
    env { occ_bs_env = extendVarEnv swap_env scrut_var (case_bndr', mco)
            , occ_bs_rng = rng_vars `extendVarSet` case_bndr'
                           `unionVarSet` tyCoVarsOfMCo mco }

      | Bool
    otherwise
      = OccEnv
    env
      where
        case_bndr' :: Id
    case_bndr' = Id -> Id
    zapIdOccInfo Id
    case_bndr
                     -- See Note [Zap case binders in proxy bindings]

    scrutBinderSwap_maybe :: OutExpr -> Maybe (OutVar, MCoercion)
    -- If (scrutBinderSwap_maybe e = Just (v, mco), then
    --    v = e |> mco
    -- See Note [Case of cast]
    -- See Note [Care with binder-swap on dictionaries]
    --
    -- We use this same function in SpecConstr, and Simplify.Iteration,
    -- when something binder-swap-like is happening
    scrutBinderSwap_maybe :: CoreExpr -> Maybe (Id, MCoercion)
    scrutBinderSwap_maybe (Var Id
    v)    = (Id, MCoercion) -> Maybe (Id, MCoercion)
    forall a. a -> Maybe a
    Just (Id
    v, MCoercion
    MRefl)
    scrutBinderSwap_maybe (Cast (Var Id
    v) CoercionR
    co)
      | Bool -> Bool
    not (Id -> Bool
    isDictId Id
    v)             = (Id, MCoercion) -> Maybe (Id, MCoercion)
    forall a. a -> Maybe a
    Just (Id
    v, CoercionR -> MCoercion
    MCo (CoercionR -> CoercionR
    mkSymCo CoercionR
    co))
            -- Cast: see Note [Case of cast]
            -- isDictId: see Note [Care with binder-swap on dictionaries]
            -- The isDictId rejects a Constraint/Constraint binder-swap, perhaps
            -- over-conservatively. But I have never seen one, so I'm leaving
            -- the code as simple as possible. Losing the binder-swap in a
            -- rare case probably has very low impact.
    scrutBinderSwap_maybe (Tick CoreTickish
    _ CoreExpr
    e) = CoreExpr -> Maybe (Id, MCoercion)
    scrutBinderSwap_maybe CoreExpr
    e  -- Drop ticks
    scrutBinderSwap_maybe CoreExpr
    _          = Maybe (Id, MCoercion)
    forall a. Maybe a
    Nothing

    lookupBndrSwap :: OccEnv -> Id -> (CoreExpr, Id)
    -- See Note [The binder-swap substitution]
    -- Returns an expression of the same type as Id
    lookupBndrSwap :: OccEnv -> Id -> (CoreExpr, Id)
    lookupBndrSwap env :: OccEnv
    env@(OccEnv { occ_bs_env :: OccEnv -> IdEnv (Id, MCoercion)
    occ_bs_env = IdEnv (Id, MCoercion)
    bs_env })  Id
    bndr
      = case IdEnv (Id, MCoercion) -> Id -> Maybe (Id, MCoercion)
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv IdEnv (Id, MCoercion)
    bs_env Id
    bndr of {
           Maybe (Id, MCoercion)
    Nothing           -> (Id -> CoreExpr
    forall b. Id -> Expr b
    Var Id
    bndr, Id
    bndr) ;
           Just (Id
    bndr1, MCoercion
    mco) ->

        -- Why do we iterate here?
        -- See (BS2) in Note [The binder-swap substitution]
        case OccEnv -> Id -> (CoreExpr, Id)
    lookupBndrSwap OccEnv
    env Id
    bndr1 of
          (CoreExpr
    fun, Id
    fun_id) -> (CoreExpr -> MCoercion -> CoreExpr
    mkCastMCo CoreExpr
    fun MCoercion
    mco, Id
    fun_id) }

    {- Historical note [Proxy let-bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We used to do the binder-swap transformation by introducing
    a proxy let-binding, thus;

       case x of b { pi -> ri }
          ==>
       case x of b { pi -> let x = b in ri }

    But that had two problems:

    1. If 'x' is an imported GlobalId, we'd end up with a GlobalId
       on the LHS of a let-binding which isn't allowed.  We worked
       around this for a while by "localising" x, but it turned
       out to be very painful #16296,

    2. In CorePrep we use the occurrence analyser to do dead-code
       elimination (see Note [Dead code in CorePrep]).  But that
       occasionally led to an unlifted let-binding
           case x of b { DEFAULT -> let x::Int# = b in ... }
       which disobeys one of CorePrep's output invariants (no unlifted
       let-bindings) -- see #5433.

    Doing a substitution (via occ_bs_env) is much better.

    Historical Note [no-case-of-case]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We *used* to suppress the binder-swap in case expressions when
    -fno-case-of-case is on.  Old remarks:
        "This happens in the first simplifier pass,
        and enhances full laziness.  Here's the bad case:
                f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
        If we eliminate the inner case, we trap it inside the I# v -> arm,
        which might prevent some full laziness happening.  I've seen this
        in action in spectral/cichelli/Prog.hs:
                 [(m,n) | m <- [1..max], n <- [1..max]]
        Hence the check for NoCaseOfCase."
    However, now the full-laziness pass itself reverses the binder-swap, so this
    check is no longer necessary.

    Historical Note [Suppressing the case binder-swap]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    This old note describes a problem that is also fixed by doing the
    binder-swap in OccAnal:

        There is another situation when it might make sense to suppress the
        case-expression binde-swap. If we have

            case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
                           ...other cases .... }

        We'll perform the binder-swap for the outer case, giving

            case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
                           ...other cases .... }

        But there is no point in doing it for the inner case, because w1 can't
        be inlined anyway.  Furthermore, doing the case-swapping involves
        zapping w2's occurrence info (see paragraphs that follow), and that
        forces us to bind w2 when doing case merging.  So we get

            case x of w1 { A -> let w2 = w1 in e1
                           B -> let w2 = w1 in e2
                           ...other cases .... }

        This is plain silly in the common case where w2 is dead.

        Even so, I can't see a good way to implement this idea.  I tried
        not doing the binder-swap if the scrutinee was already evaluated
        but that failed big-time:

                data T = MkT !Int

                case v of w  { MkT x ->
                case x of x1 { I# y1 ->
                case x of x2 { I# y2 -> ...

        Notice that because MkT is strict, x is marked "evaluated".  But to
        eliminate the last case, we must either make sure that x (as well as
        x1) has unfolding MkT y1.  The straightforward thing to do is to do
        the binder-swap.  So this whole note is a no-op.

    It's fixed by doing the binder-swap in OccAnal because we can do the
    binder-swap unconditionally and still get occurrence analysis
    information right.

    ************************************************************************
    *                                                                      *
    \subsection[OccurAnal-types]{OccEnv}
    *                                                                      *
    ************************************************************************

    Note [UsageDetails and zapping]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    On many occasions, we must modify all gathered occurrence data at once. For
    instance, all occurrences underneath a (non-one-shot) lambda set the
    'occ_in_lam' flag to become 'True'. We could use 'mapVarEnv' to do this, but
    that takes O(n) time and we will do this often---in particular, there are many
    places where tail calls are not allowed, and each of these causes all variables
    to get marked with 'NoTailCallInfo'.

    Instead of relying on `mapVarEnv`, then, we carry three 'IdEnv's around along
    with the 'OccInfoEnv'. Each of these extra environments is a "zapped set"
    recording which variables have been zapped in some way. Zapping all occurrence
    info then simply means setting the corresponding zapped set to the whole
    'OccInfoEnv', a fast O(1) operation.

    Note [LocalOcc]
    ~~~~~~~~~~~~~~~
    LocalOcc is used purely internally, in the occurrence analyser.  It differs from
    GHC.Types.Basic.OccInfo because it has only OneOcc and ManyOcc; it does not need
    IAmDead or IAmALoopBreaker.

    Note that `OneOccL` doesn't meant that it occurs /syntactially/ only once; it
    means that it is /used/ only once. It might occur syntactically many times.
    For example, in (case x of A -> y; B -> y; C -> True),
    * `y` is used only once
    * but it occurs syntactically twice

    -}

    type OccInfoEnv = IdEnv LocalOcc  -- A finite map from an expression's
                                      -- free variables to their usage

    data LocalOcc  -- See Note [LocalOcc]
         = OneOccL { LocalOcc -> JoinArity
    lo_n_br  :: {-# UNPACK #-} !BranchCount  -- Number of syntactic occurrences
                   , LocalOcc -> TailCallInfo
    lo_tail  :: !TailCallInfo
                       -- Combining (AlwaysTailCalled 2) and (AlwaysTailCalled 3)
                       -- gives NoTailCallInfo
                  , LocalOcc -> InterestingCxt
    lo_int_cxt :: !InterestingCxt }
        | ManyOccL !TailCallInfo

    instance Outputable LocalOcc where
      ppr :: LocalOcc -> SDoc
    ppr (OneOccL { lo_n_br :: LocalOcc -> JoinArity
    lo_n_br = JoinArity
    n, lo_tail :: LocalOcc -> TailCallInfo
    lo_tail = TailCallInfo
    tci })
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "OneOccL" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces (JoinArity -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr JoinArity
    n SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc
    forall doc. IsLine doc => doc
    comma SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> TailCallInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TailCallInfo
    tci)
      ppr (ManyOccL TailCallInfo
    tci) = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ManyOccL" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces (TailCallInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TailCallInfo
    tci)

    localTailCallInfo :: LocalOcc -> TailCallInfo
    localTailCallInfo :: LocalOcc -> TailCallInfo
    localTailCallInfo (OneOccL  { lo_tail :: LocalOcc -> TailCallInfo
    lo_tail = TailCallInfo
    tci }) = TailCallInfo
    tci
    localTailCallInfo (ManyOccL TailCallInfo
    tci)               = TailCallInfo
    tci

    type ZappedSet = OccInfoEnv -- Values are ignored

    data UsageDetails
      = UD { UsageDetails -> VarEnv LocalOcc
    ud_env       :: !OccInfoEnv
           , UsageDetails -> VarEnv LocalOcc
    ud_z_many    :: !ZappedSet   -- apply 'markMany' to these
           , UsageDetails -> VarEnv LocalOcc
    ud_z_in_lam  :: !ZappedSet   -- apply 'markInsideLam' to these
           , UsageDetails -> VarEnv LocalOcc
    ud_z_tail    :: !ZappedSet   -- zap tail-call info for these
           }
      -- INVARIANT: All three zapped sets are subsets of ud_env

    instance Outputable UsageDetails where
      ppr :: UsageDetails -> SDoc
    ppr ud :: UsageDetails
    ud@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env, ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail = VarEnv LocalOcc
    z_tail })
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "UD" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> (SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces (SDoc -> SDoc) -> SDoc -> SDoc
    forall a b. (a -> b) -> a -> b
    $ [SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    fsep ([SDoc] -> SDoc) -> [SDoc] -> SDoc
    forall a b. (a -> b) -> a -> b
    $ SDoc -> [SDoc] -> [SDoc]
    forall doc. IsLine doc => doc -> [doc] -> [doc]
    punctuate SDoc
    forall doc. IsLine doc => doc
    comma ([SDoc] -> [SDoc]) -> [SDoc] -> [SDoc]
    forall a b. (a -> b) -> a -> b
    $
          [ Unique -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Unique
    uq SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    ":->" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OccInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (UsageDetails -> Unique -> OccInfo
    lookupOccInfoByUnique UsageDetails
    ud Unique
    uq)
          | (Unique
    uq, LocalOcc
    _) <- (Unique
     -> LocalOcc -> [(Unique, LocalOcc)] -> [(Unique, LocalOcc)])
    -> [(Unique, LocalOcc)] -> VarEnv LocalOcc -> [(Unique, LocalOcc)]
    forall a r. (Unique -> a -> r -> r) -> r -> VarEnv a -> r
    nonDetStrictFoldVarEnv_Directly Unique -> LocalOcc -> [(Unique, LocalOcc)] -> [(Unique, LocalOcc)]
    do_one [] VarEnv LocalOcc
    env ])
          SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ JoinArity -> SDoc -> SDoc
    nest JoinArity
    2 (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ud_z_tail" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> VarEnv LocalOcc -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr VarEnv LocalOcc
    z_tail)
        where
          do_one :: Unique -> LocalOcc -> [(Unique,LocalOcc)] -> [(Unique,LocalOcc)]
          do_one :: Unique -> LocalOcc -> [(Unique, LocalOcc)] -> [(Unique, LocalOcc)]
    do_one Unique
    uniq LocalOcc
    occ [(Unique, LocalOcc)]
    occs = (Unique
    uniq, LocalOcc
    occ) (Unique, LocalOcc) -> [(Unique, LocalOcc)] -> [(Unique, LocalOcc)]
    forall a. a -> [a] -> [a]
    : [(Unique, LocalOcc)]
    occs

    ---------------------
    -- | TailUsageDetails captures the result of applying 'occAnalLamTail'
    --   to a function `\xyz.body`. The TailUsageDetails pairs together
    --   * the number of lambdas (including type lambdas: a JoinArity)
    --   * UsageDetails for the `body` of the lambda, unadjusted by `adjustTailUsage`.
    -- If the binding turns out to be a join point with the indicated join
    -- arity, this unadjusted usage details is just what we need; otherwise we
    -- need to discard tail calls. That's what `adjustTailUsage` does.
    data TailUsageDetails = TUD !JoinArity !UsageDetails

    instance Outputable TailUsageDetails where
      ppr :: TailUsageDetails -> SDoc
    ppr (TUD JoinArity
    ja UsageDetails
    uds) = SDoc
    lambda SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> JoinArity -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr JoinArity
    ja SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> UsageDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr UsageDetails
    uds

    ---------------------
    data WithUsageDetails     a = WUD  !UsageDetails     !a
    data WithTailUsageDetails a = WTUD !TailUsageDetails !a

    -------------------
    -- UsageDetails API

    andUDs, orUDs
            :: UsageDetails -> UsageDetails -> UsageDetails
    andUDs :: UsageDetails -> UsageDetails -> UsageDetails
    andUDs = (LocalOcc -> LocalOcc -> LocalOcc)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith LocalOcc -> LocalOcc -> LocalOcc
    andLocalOcc
    orUDs :: UsageDetails -> UsageDetails -> UsageDetails
    orUDs  = (LocalOcc -> LocalOcc -> LocalOcc)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith LocalOcc -> LocalOcc -> LocalOcc
    orLocalOcc

    mkOneOcc :: OccEnv -> Id -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc :: OccEnv -> Id -> InterestingCxt -> JoinArity -> UsageDetails
    mkOneOcc !OccEnv
    env Id
    id InterestingCxt
    int_cxt JoinArity
    arity
      | Bool -> Bool
    not (Id -> Bool
    isLocalId Id
    id)
      = UsageDetails
    emptyDetails

      | Just VarEnv LocalOcc
    join_uds <- JoinPointInfo -> Id -> Maybe (VarEnv LocalOcc)
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv (OccEnv -> JoinPointInfo
    occ_join_points OccEnv
    env) Id
    id
      = -- See Note [Occurrence analysis for join points]
        Bool -> SDoc -> UsageDetails -> UsageDetails
    forall a. HasCallStack => Bool -> SDoc -> a -> a
    assertPpr (Bool -> Bool
    not (VarEnv LocalOcc -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv LocalOcc
    join_uds)) (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    id) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
           -- We only put non-empty join-points into occ_join_points
        VarEnv LocalOcc -> UsageDetails
    mkSimpleDetails (VarEnv LocalOcc -> Id -> LocalOcc -> VarEnv LocalOcc
    forall a. VarEnv a -> Id -> a -> VarEnv a
    extendVarEnv VarEnv LocalOcc
    join_uds Id
    id LocalOcc
    occ)

      | Bool
    otherwise
      = VarEnv LocalOcc -> UsageDetails
    mkSimpleDetails (Id -> LocalOcc -> VarEnv LocalOcc
    forall a. Id -> a -> VarEnv a
    unitVarEnv Id
    id LocalOcc
    occ)

      where
        occ :: LocalOcc
    occ = OneOccL { lo_n_br :: JoinArity
    lo_n_br = JoinArity
    1, lo_int_cxt :: InterestingCxt
    lo_int_cxt = InterestingCxt
    int_cxt
                      , lo_tail :: TailCallInfo
    lo_tail = JoinArity -> TailCallInfo
    AlwaysTailCalled JoinArity
    arity }

    -- Add several occurrences, assumed not to be tail calls
    add_many_occ :: Var -> OccInfoEnv -> OccInfoEnv
    add_many_occ :: Id -> VarEnv LocalOcc -> VarEnv LocalOcc
    add_many_occ Id
    v VarEnv LocalOcc
    env | Id -> Bool
    isId Id
    v    = VarEnv LocalOcc -> Id -> LocalOcc -> VarEnv LocalOcc
    forall a. VarEnv a -> Id -> a -> VarEnv a
    extendVarEnv VarEnv LocalOcc
    env Id
    v (TailCallInfo -> LocalOcc
    ManyOccL TailCallInfo
    NoTailCallInfo)
                       | Bool
    otherwise = VarEnv LocalOcc
    env
            -- Give a non-committal binder info (i.e noOccInfo) because
            --   a) Many copies of the specialised thing can appear
            --   b) We don't want to substitute a BIG expression inside a RULE
            --      even if that's the only occurrence of the thing
            --      (Same goes for INLINE.)

    addManyOccs :: UsageDetails -> VarSet -> UsageDetails
    addManyOccs :: UsageDetails -> VarSet -> UsageDetails
    addManyOccs UsageDetails
    uds VarSet
    var_set
      | VarSet -> Bool
    isEmptyVarSet VarSet
    var_set = UsageDetails
    uds
      | Bool
    otherwise             = UsageDetails
    uds { ud_env = add_to (ud_env uds) }
      where
        add_to :: VarEnv LocalOcc -> VarEnv LocalOcc
    add_to VarEnv LocalOcc
    env = (Id -> VarEnv LocalOcc -> VarEnv LocalOcc)
    -> VarEnv LocalOcc -> VarSet -> VarEnv LocalOcc
    forall elt a. (elt -> a -> a) -> a -> UniqSet elt -> a
    nonDetStrictFoldUniqSet Id -> VarEnv LocalOcc -> VarEnv LocalOcc
    add_many_occ VarEnv LocalOcc
    env VarSet
    var_set
        -- It's OK to use nonDetStrictFoldUniqSet here because add_many_occ commutes

    addLamCoVarOccs :: UsageDetails -> [Var] -> UsageDetails
    -- Add any CoVars free in the type of a lambda-binder
    -- See Note [Gather occurrences of coercion variables]
    addLamCoVarOccs :: UsageDetails -> [Id] -> UsageDetails
    addLamCoVarOccs UsageDetails
    uds [Id]
    bndrs
      = (Id -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [Id] -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr Id -> UsageDetails -> UsageDetails
    add UsageDetails
    uds [Id]
    bndrs
      where
        add :: Id -> UsageDetails -> UsageDetails
    add Id
    bndr UsageDetails
    uds = UsageDetails
    uds UsageDetails -> VarSet -> UsageDetails
    `addManyOccs` Type -> VarSet
    coVarsOfType (Id -> Type
    varType Id
    bndr)

    emptyDetails :: UsageDetails
    emptyDetails :: UsageDetails
    emptyDetails = VarEnv LocalOcc -> UsageDetails
    mkSimpleDetails VarEnv LocalOcc
    forall a. VarEnv a
    emptyVarEnv

    isEmptyDetails :: UsageDetails -> Bool
    isEmptyDetails :: UsageDetails -> Bool
    isEmptyDetails (UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = VarEnv LocalOcc -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv LocalOcc
    env

    mkSimpleDetails :: OccInfoEnv -> UsageDetails
    mkSimpleDetails :: VarEnv LocalOcc -> UsageDetails
    mkSimpleDetails VarEnv LocalOcc
    env = UD { ud_env :: VarEnv LocalOcc
    ud_env       = VarEnv LocalOcc
    env
                             , ud_z_many :: VarEnv LocalOcc
    ud_z_many    = VarEnv LocalOcc
    forall a. VarEnv a
    emptyVarEnv
                             , ud_z_in_lam :: VarEnv LocalOcc
    ud_z_in_lam  = VarEnv LocalOcc
    forall a. VarEnv a
    emptyVarEnv
                             , ud_z_tail :: VarEnv LocalOcc
    ud_z_tail    = VarEnv LocalOcc
    forall a. VarEnv a
    emptyVarEnv }

    modifyUDEnv :: (OccInfoEnv -> OccInfoEnv) -> UsageDetails -> UsageDetails
    modifyUDEnv :: (VarEnv LocalOcc -> VarEnv LocalOcc)
    -> UsageDetails -> UsageDetails
    modifyUDEnv VarEnv LocalOcc -> VarEnv LocalOcc
    f uds :: UsageDetails
    uds@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = UsageDetails
    uds { ud_env = f env }

    delBndrsFromUDs :: [Var] -> UsageDetails -> UsageDetails
    -- Delete these binders from the UsageDetails
    delBndrsFromUDs :: [Id] -> UsageDetails -> UsageDetails
    delBndrsFromUDs [Id]
    bndrs (UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env, ud_z_many :: UsageDetails -> VarEnv LocalOcc
    ud_z_many = VarEnv LocalOcc
    z_many
                              , ud_z_in_lam :: UsageDetails -> VarEnv LocalOcc
    ud_z_in_lam  = VarEnv LocalOcc
    z_in_lam, ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail = VarEnv LocalOcc
    z_tail })
      = UD { ud_env :: VarEnv LocalOcc
    ud_env       = VarEnv LocalOcc
    env      VarEnv LocalOcc -> [Id] -> VarEnv LocalOcc
    forall a. VarEnv a -> [Id] -> VarEnv a
    `delVarEnvList` [Id]
    bndrs
           , ud_z_many :: VarEnv LocalOcc
    ud_z_many    = VarEnv LocalOcc
    z_many   VarEnv LocalOcc -> [Id] -> VarEnv LocalOcc
    forall a. VarEnv a -> [Id] -> VarEnv a
    `delVarEnvList` [Id]
    bndrs
           , ud_z_in_lam :: VarEnv LocalOcc
    ud_z_in_lam  = VarEnv LocalOcc
    z_in_lam VarEnv LocalOcc -> [Id] -> VarEnv LocalOcc
    forall a. VarEnv a -> [Id] -> VarEnv a
    `delVarEnvList` [Id]
    bndrs
           , ud_z_tail :: VarEnv LocalOcc
    ud_z_tail    = VarEnv LocalOcc
    z_tail   VarEnv LocalOcc -> [Id] -> VarEnv LocalOcc
    forall a. VarEnv a -> [Id] -> VarEnv a
    `delVarEnvList` [Id]
    bndrs }

    markAllMany, markAllInsideLam, markAllNonTail, markAllManyNonTail
      :: UsageDetails -> UsageDetails
    markAllMany :: UsageDetails -> UsageDetails
    markAllMany      ud :: UsageDetails
    ud@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = UsageDetails
    ud { ud_z_many   = env }
    markAllInsideLam :: UsageDetails -> UsageDetails
    markAllInsideLam ud :: UsageDetails
    ud@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = UsageDetails
    ud { ud_z_in_lam = env }
    markAllNonTail :: UsageDetails -> UsageDetails
    markAllNonTail   ud :: UsageDetails
    ud@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = UsageDetails
    ud { ud_z_tail   = env }
    markAllManyNonTail :: UsageDetails -> UsageDetails
    markAllManyNonTail = UsageDetails -> UsageDetails
    markAllMany (UsageDetails -> UsageDetails)
    -> (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . UsageDetails -> UsageDetails
    markAllNonTail -- effectively sets to noOccInfo

    markAllInsideLamIf, markAllNonTailIf :: Bool -> UsageDetails -> UsageDetails

    markAllInsideLamIf :: Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf  Bool
    True  UsageDetails
    ud = UsageDetails -> UsageDetails
    markAllInsideLam UsageDetails
    ud
    markAllInsideLamIf  Bool
    False UsageDetails
    ud = UsageDetails
    ud

    markAllNonTailIf :: Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf Bool
    True  UsageDetails
    ud = UsageDetails -> UsageDetails
    markAllNonTail UsageDetails
    ud
    markAllNonTailIf Bool
    False UsageDetails
    ud = UsageDetails
    ud

    lookupTailCallInfo :: UsageDetails -> Id -> TailCallInfo
    lookupTailCallInfo :: UsageDetails -> Id -> TailCallInfo
    lookupTailCallInfo UsageDetails
    uds Id
    id
      | UD { ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail = VarEnv LocalOcc
    z_tail, ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env } <- UsageDetails
    uds
      , Bool -> Bool
    not (Id
    id Id -> VarEnv LocalOcc -> Bool
    forall a. Id -> VarEnv a -> Bool
    `elemVarEnv` VarEnv LocalOcc
    z_tail)
      , Just LocalOcc
    occ <- VarEnv LocalOcc -> Id -> Maybe LocalOcc
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv VarEnv LocalOcc
    env Id
    id
      = LocalOcc -> TailCallInfo
    localTailCallInfo LocalOcc
    occ
      | Bool
    otherwise
      = TailCallInfo
    NoTailCallInfo

    udFreeVars :: VarSet -> UsageDetails -> VarSet
    -- Find the subset of bndrs that are mentioned in uds
    udFreeVars :: VarSet -> UsageDetails -> VarSet
    udFreeVars VarSet
    bndrs (UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env }) = VarSet -> VarEnv LocalOcc -> VarSet
    restrictFreeVars VarSet
    bndrs VarEnv LocalOcc
    env

    restrictFreeVars :: VarSet -> OccInfoEnv -> VarSet
    restrictFreeVars :: VarSet -> VarEnv LocalOcc -> VarSet
    restrictFreeVars VarSet
    bndrs VarEnv LocalOcc
    fvs = VarSet -> VarEnv LocalOcc -> VarSet
    forall key b. UniqSet key -> UniqFM key b -> UniqSet key
    restrictUniqSetToUFM VarSet
    bndrs VarEnv LocalOcc
    fvs

    -------------------
    -- Auxiliary functions for UsageDetails implementation

    combineUsageDetailsWith :: (LocalOcc -> LocalOcc -> LocalOcc)
                            -> UsageDetails -> UsageDetails -> UsageDetails
    {-# INLINE combineUsageDetailsWith #-}
    combineUsageDetailsWith :: (LocalOcc -> LocalOcc -> LocalOcc)
    -> UsageDetails -> UsageDetails -> UsageDetails
    combineUsageDetailsWith LocalOcc -> LocalOcc -> LocalOcc
    plus_occ_info
        uds1 :: UsageDetails
    uds1@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env1, ud_z_many :: UsageDetails -> VarEnv LocalOcc
    ud_z_many = VarEnv LocalOcc
    z_many1, ud_z_in_lam :: UsageDetails -> VarEnv LocalOcc
    ud_z_in_lam = VarEnv LocalOcc
    z_in_lam1, ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail = VarEnv LocalOcc
    z_tail1 })
        uds2 :: UsageDetails
    uds2@(UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env = VarEnv LocalOcc
    env2, ud_z_many :: UsageDetails -> VarEnv LocalOcc
    ud_z_many = VarEnv LocalOcc
    z_many2, ud_z_in_lam :: UsageDetails -> VarEnv LocalOcc
    ud_z_in_lam = VarEnv LocalOcc
    z_in_lam2, ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail = VarEnv LocalOcc
    z_tail2 })
      | VarEnv LocalOcc -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv LocalOcc
    env1 = UsageDetails
    uds2
      | VarEnv LocalOcc -> Bool
    forall a. VarEnv a -> Bool
    isEmptyVarEnv VarEnv LocalOcc
    env2 = UsageDetails
    uds1
      | Bool
    otherwise
      = UD { ud_env :: VarEnv LocalOcc
    ud_env       = (LocalOcc -> LocalOcc -> LocalOcc)
    -> VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall a. (a -> a -> a) -> VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv_C LocalOcc -> LocalOcc -> LocalOcc
    plus_occ_info VarEnv LocalOcc
    env1 VarEnv LocalOcc
    env2
           , ud_z_many :: VarEnv LocalOcc
    ud_z_many    = VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv VarEnv LocalOcc
    z_many1   VarEnv LocalOcc
    z_many2
           , ud_z_in_lam :: VarEnv LocalOcc
    ud_z_in_lam  = VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv VarEnv LocalOcc
    z_in_lam1 VarEnv LocalOcc
    z_in_lam2
           , ud_z_tail :: VarEnv LocalOcc
    ud_z_tail    = VarEnv LocalOcc -> VarEnv LocalOcc -> VarEnv LocalOcc
    forall a. VarEnv a -> VarEnv a -> VarEnv a
    plusVarEnv VarEnv LocalOcc
    z_tail1   VarEnv LocalOcc
    z_tail2 }

    lookupLetOccInfo :: UsageDetails -> Id -> OccInfo
    -- Don't use locally-generated occ_info for exported (visible-elsewhere)
    -- things.  Instead just give noOccInfo.
    -- NB: setBinderOcc will (rightly) erase any LoopBreaker info;
    --     we are about to re-generate it and it shouldn't be "sticky"
    lookupLetOccInfo :: UsageDetails -> Id -> OccInfo
    lookupLetOccInfo UsageDetails
    ud Id
    id
     | Id -> Bool
    isExportedId Id
    id = OccInfo
    noOccInfo
     | Bool
    otherwise       = UsageDetails -> Unique -> OccInfo
    lookupOccInfoByUnique UsageDetails
    ud (Id -> Unique
    idUnique Id
    id)

    lookupOccInfo :: UsageDetails -> Id -> OccInfo
    lookupOccInfo :: UsageDetails -> Id -> OccInfo
    lookupOccInfo UsageDetails
    ud Id
    id = UsageDetails -> Unique -> OccInfo
    lookupOccInfoByUnique UsageDetails
    ud (Id -> Unique
    idUnique Id
    id)

    lookupOccInfoByUnique :: UsageDetails -> Unique -> OccInfo
    lookupOccInfoByUnique :: UsageDetails -> Unique -> OccInfo
    lookupOccInfoByUnique (UD { ud_env :: UsageDetails -> VarEnv LocalOcc
    ud_env       = VarEnv LocalOcc
    env
                              , ud_z_many :: UsageDetails -> VarEnv LocalOcc
    ud_z_many    = VarEnv LocalOcc
    z_many
                              , ud_z_in_lam :: UsageDetails -> VarEnv LocalOcc
    ud_z_in_lam  = VarEnv LocalOcc
    z_in_lam
                              , ud_z_tail :: UsageDetails -> VarEnv LocalOcc
    ud_z_tail    = VarEnv LocalOcc
    z_tail })
                      Unique
    uniq
      = case VarEnv LocalOcc -> Unique -> Maybe LocalOcc
    forall a. VarEnv a -> Unique -> Maybe a
    lookupVarEnv_Directly VarEnv LocalOcc
    env Unique
    uniq of
          Maybe LocalOcc
    Nothing -> OccInfo
    IAmDead
          Just (OneOccL { lo_n_br :: LocalOcc -> JoinArity
    lo_n_br = JoinArity
    n_br, lo_int_cxt :: LocalOcc -> InterestingCxt
    lo_int_cxt = InterestingCxt
    int_cxt
                        , lo_tail :: LocalOcc -> TailCallInfo
    lo_tail = TailCallInfo
    tail_info })
              | Unique
    uniq Unique -> VarEnv LocalOcc -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey`VarEnv LocalOcc
    z_many
              -> ManyOccs { occ_tail :: TailCallInfo
    occ_tail = TailCallInfo -> TailCallInfo
    mk_tail_info TailCallInfo
    tail_info }
              | Bool
    otherwise
              -> OneOcc { occ_in_lam :: InsideLam
    occ_in_lam  = InsideLam
    in_lam
                        , occ_n_br :: JoinArity
    occ_n_br    = JoinArity
    n_br
                        , occ_int_cxt :: InterestingCxt
    occ_int_cxt = InterestingCxt
    int_cxt
                        , occ_tail :: TailCallInfo
    occ_tail    = TailCallInfo -> TailCallInfo
    mk_tail_info TailCallInfo
    tail_info }
             where
               in_lam :: InsideLam
    in_lam | Unique
    uniq Unique -> VarEnv LocalOcc -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` VarEnv LocalOcc
    z_in_lam = InsideLam
    IsInsideLam
                      | Bool
    otherwise                       = InsideLam
    NotInsideLam

          Just (ManyOccL TailCallInfo
    tail_info) -> ManyOccs { occ_tail :: TailCallInfo
    occ_tail = TailCallInfo -> TailCallInfo
    mk_tail_info TailCallInfo
    tail_info }
      where
        mk_tail_info :: TailCallInfo -> TailCallInfo
    mk_tail_info TailCallInfo
    ti
            | Unique
    uniq Unique -> VarEnv LocalOcc -> Bool
    forall a. Unique -> VarEnv a -> Bool
    `elemVarEnvByKey` VarEnv LocalOcc
    z_tail = TailCallInfo
    NoTailCallInfo
            | Bool
    otherwise                     = TailCallInfo
    ti

    -------------------
    -- See Note [Adjusting right-hand sides]

    adjustNonRecRhs :: JoinPointHood
                    -> WithTailUsageDetails CoreExpr
                    -> WithUsageDetails CoreExpr
    -- ^ This function concentrates shared logic between occAnalNonRecBind and the
    -- AcyclicSCC case of occAnalRec.
    -- It returns the adjusted rhs UsageDetails combined with the body usage
    adjustNonRecRhs :: JoinPointHood
    -> WithTailUsageDetails CoreExpr -> WithUsageDetails CoreExpr
    adjustNonRecRhs JoinPointHood
    mb_join_arity rhs_wuds :: WithTailUsageDetails CoreExpr
    rhs_wuds@(WTUD TailUsageDetails
    _ CoreExpr
    rhs)
      = UsageDetails -> CoreExpr -> WithUsageDetails CoreExpr
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD (JoinPointHood -> WithTailUsageDetails CoreExpr -> UsageDetails
    adjustTailUsage JoinPointHood
    mb_join_arity WithTailUsageDetails CoreExpr
    rhs_wuds) CoreExpr
    rhs

    adjustTailUsage :: JoinPointHood
                    -> WithTailUsageDetails CoreExpr    -- Rhs usage, AFTER occAnalLamTail
                    -> UsageDetails
    adjustTailUsage :: JoinPointHood -> WithTailUsageDetails CoreExpr -> UsageDetails
    adjustTailUsage JoinPointHood
    mb_join_arity (WTUD (TUD JoinArity
    rhs_ja UsageDetails
    uds) CoreExpr
    rhs)
      = -- c.f. occAnal (Lam {})
        Bool -> UsageDetails -> UsageDetails
    markAllInsideLamIf (Bool -> Bool
    not Bool
    one_shot) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
        Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf (Bool -> Bool
    not Bool
    exact_join) (UsageDetails -> UsageDetails) -> UsageDetails -> UsageDetails
    forall a b. (a -> b) -> a -> b
    $
        UsageDetails
    uds
      where
        one_shot :: Bool
    one_shot   = CoreExpr -> Bool
    isOneShotFun CoreExpr
    rhs
        exact_join :: Bool
    exact_join = JoinPointHood
    mb_join_arity JoinPointHood -> JoinPointHood -> Bool
    forall a. Eq a => a -> a -> Bool
    == JoinArity -> JoinPointHood
    JoinPoint JoinArity
    rhs_ja

    adjustTailArity :: JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity :: JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity JoinPointHood
    mb_rhs_ja (TUD JoinArity
    ja UsageDetails
    usage)
      = Bool -> UsageDetails -> UsageDetails
    markAllNonTailIf (JoinPointHood
    mb_rhs_ja JoinPointHood -> JoinPointHood -> Bool
    forall a. Eq a => a -> a -> Bool
    /= JoinArity -> JoinPointHood
    JoinPoint JoinArity
    ja) UsageDetails
    usage

    type IdWithOccInfo = Id

    tagLamBinders :: UsageDetails        -- Of scope
                  -> [Id]                -- Binders
                  -> [IdWithOccInfo]     -- Tagged binders
    tagLamBinders :: UsageDetails -> [Id] -> [Id]
    tagLamBinders UsageDetails
    usage [Id]
    binders
      = (Id -> Id) -> [Id] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (UsageDetails -> Id -> Id
    tagLamBinder UsageDetails
    usage) [Id]
    binders

    tagLamBinder :: UsageDetails       -- Of scope
                 -> Id                 -- Binder
                 -> IdWithOccInfo      -- Tagged binders
    -- Used for lambda and case binders
    -- No-op on TyVars
    -- A lambda binder never has an unfolding, so no need to look for that
    tagLamBinder :: UsageDetails -> Id -> Id
    tagLamBinder UsageDetails
    usage Id
    bndr
      = OccInfo -> Id -> Id
    setBinderOcc (OccInfo -> OccInfo
    markNonTail OccInfo
    occ) Id
    bndr
          -- markNonTail: don't try to make an argument into a join point
      where
        occ :: OccInfo
    occ = UsageDetails -> Id -> OccInfo
    lookupOccInfo UsageDetails
    usage Id
    bndr

    tagNonRecBinder :: TopLevelFlag           -- At top level?
                    -> OccInfo                -- Of scope
                    -> CoreBndr               -- Binder
                    -> (IdWithOccInfo, JoinPointHood)  -- Tagged binder
    -- No-op on TyVars
    -- Precondition: OccInfo is not IAmDead
    tagNonRecBinder :: TopLevelFlag -> OccInfo -> Id -> (Id, JoinPointHood)
    tagNonRecBinder TopLevelFlag
    lvl OccInfo
    occ Id
    bndr
      | TopLevelFlag -> Id -> TailCallInfo -> Bool
    okForJoinPoint TopLevelFlag
    lvl Id
    bndr TailCallInfo
    tail_call_info
      , AlwaysTailCalled JoinArity
    ar <- TailCallInfo
    tail_call_info
      = (OccInfo -> Id -> Id
    setBinderOcc OccInfo
    occ Id
    bndr,        JoinArity -> JoinPointHood
    JoinPoint JoinArity
    ar)
      | Bool
    otherwise
      = (OccInfo -> Id -> Id
    setBinderOcc OccInfo
    zapped_occ Id
    bndr, JoinPointHood
    NotJoinPoint)
     where
        tail_call_info :: TailCallInfo
    tail_call_info = OccInfo -> TailCallInfo
    tailCallInfo OccInfo
    occ
        zapped_occ :: OccInfo
    zapped_occ     = OccInfo -> OccInfo
    markNonTail OccInfo
    occ

    tagRecBinders :: TopLevelFlag           -- At top level?
                  -> UsageDetails           -- Of body of let ONLY
                  -> [NodeDetails]
                  -> WithUsageDetails       -- Adjusted details for whole scope,
                                            -- with binders removed
                      [IdWithOccInfo]       -- Tagged binders
    -- Substantially more complicated than non-recursive case. Need to adjust RHS
    -- details *before* tagging binders (because the tags depend on the RHSes).
    tagRecBinders :: TopLevelFlag
    -> UsageDetails -> [NodeDetails] -> WithUsageDetails [Id]
    tagRecBinders TopLevelFlag
    lvl UsageDetails
    body_uds [NodeDetails]
    details_s
     = let
         bndrs :: [Id]
    bndrs = (NodeDetails -> Id) -> [NodeDetails] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map NodeDetails -> Id
    nd_bndr [NodeDetails]
    details_s

         -- 1. See Note [Join arity prediction based on joinRhsArity]
         --    Determine possible join-point-hood of whole group, by testing for
         --    manifest join arity M.
         --    This (re-)asserts that makeNode had made tuds for that same arity M!
         unadj_uds :: UsageDetails
    unadj_uds = (NodeDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [NodeDetails] -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (UsageDetails -> UsageDetails -> UsageDetails
    andUDs (UsageDetails -> UsageDetails -> UsageDetails)
    -> (NodeDetails -> UsageDetails)
    -> NodeDetails
    -> UsageDetails
    -> UsageDetails
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . NodeDetails -> UsageDetails
    test_manifest_arity) UsageDetails
    body_uds [NodeDetails]
    details_s
         test_manifest_arity :: NodeDetails -> UsageDetails
    test_manifest_arity ND{nd_rhs :: NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs = WTUD TailUsageDetails
    tuds CoreExpr
    rhs}
           = JoinPointHood -> TailUsageDetails -> UsageDetails
    adjustTailArity (JoinArity -> JoinPointHood
    JoinPoint (CoreExpr -> JoinArity
    joinRhsArity CoreExpr
    rhs)) TailUsageDetails
    tuds

         will_be_joins :: Bool
    will_be_joins = TopLevelFlag -> UsageDetails -> [Id] -> Bool
    decideRecJoinPointHood TopLevelFlag
    lvl UsageDetails
    unadj_uds [Id]
    bndrs

         mb_join_arity :: Id -> JoinPointHood
         -- mb_join_arity: See Note [Join arity prediction based on joinRhsArity]
         -- This is the source O
         mb_join_arity :: Id -> JoinPointHood
    mb_join_arity Id
    bndr
             -- Can't use willBeJoinId_maybe here because we haven't tagged
             -- the binder yet (the tag depends on these adjustments!)
           | Bool
    will_be_joins
           , AlwaysTailCalled JoinArity
    arity <- UsageDetails -> Id -> TailCallInfo
    lookupTailCallInfo UsageDetails
    unadj_uds Id
    bndr
           = JoinArity -> JoinPointHood
    JoinPoint JoinArity
    arity
           | Bool
    otherwise
           = Bool -> JoinPointHood -> JoinPointHood
    forall a. HasCallStack => Bool -> a -> a
    assert (Bool -> Bool
    not Bool
    will_be_joins) -- Should be AlwaysTailCalled if
             JoinPointHood
    NotJoinPoint               -- we are making join points!

         -- 2. Adjust usage details of each RHS, taking into account the
         --    join-point-hood decision
         rhs_udss' :: [UsageDetails]
    rhs_udss' = [ JoinPointHood -> WithTailUsageDetails CoreExpr -> UsageDetails
    adjustTailUsage (Id -> JoinPointHood
    mb_join_arity Id
    bndr) WithTailUsageDetails CoreExpr
    rhs_wuds
                         -- Matching occAnalLamTail in makeNode
                     | ND { nd_bndr :: NodeDetails -> Id
    nd_bndr = Id
    bndr, nd_rhs :: NodeDetails -> WithTailUsageDetails CoreExpr
    nd_rhs = WithTailUsageDetails CoreExpr
    rhs_wuds } <- [NodeDetails]
    details_s ]

         -- 3. Compute final usage details from adjusted RHS details
         adj_uds :: UsageDetails
    adj_uds = (UsageDetails -> UsageDetails -> UsageDetails)
    -> UsageDetails -> [UsageDetails] -> UsageDetails
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr UsageDetails -> UsageDetails -> UsageDetails
    andUDs UsageDetails
    body_uds [UsageDetails]
    rhs_udss'

         -- 4. Tag each binder with its adjusted details
         bndrs' :: [Id]
    bndrs'    = [ OccInfo -> Id -> Id
    setBinderOcc (UsageDetails -> Id -> OccInfo
    lookupLetOccInfo UsageDetails
    adj_uds Id
    bndr) Id
    bndr
                     | Id
    bndr <- [Id]
    bndrs ]

       in
       UsageDetails -> [Id] -> WithUsageDetails [Id]
    forall a. UsageDetails -> a -> WithUsageDetails a
    WUD UsageDetails
    adj_uds [Id]
    bndrs'

    setBinderOcc :: OccInfo -> CoreBndr -> CoreBndr
    setBinderOcc :: OccInfo -> Id -> Id
    setBinderOcc OccInfo
    occ_info Id
    bndr
      | Id -> Bool
    isTyVar Id
    bndr               = Id
    bndr
      | OccInfo
    occ_info OccInfo -> OccInfo -> Bool
    forall a. Eq a => a -> a -> Bool
    == Id -> OccInfo
    idOccInfo Id
    bndr = Id
    bndr
      | Bool
    otherwise                  = Id -> OccInfo -> Id
    setIdOccInfo Id
    bndr OccInfo
    occ_info

    -- | Decide whether some bindings should be made into join points or not, based
    -- on its occurrences. This is
    -- Returns `False` if they can't be join points. Note that it's an
    -- all-or-nothing decision, as if multiple binders are given, they're
    -- assumed to be mutually recursive.
    --
    -- It must, however, be a final decision. If we say `True` for 'f',
    -- and then subsequently decide /not/ make 'f' into a join point, then
    -- the decision about another binding 'g' might be invalidated if (say)
    -- 'f' tail-calls 'g'.
    --
    -- See Note [Invariants on join points] in "GHC.Core".
    decideRecJoinPointHood :: TopLevelFlag -> UsageDetails
                           -> [CoreBndr] -> Bool
    decideRecJoinPointHood :: TopLevelFlag -> UsageDetails -> [Id] -> Bool
    decideRecJoinPointHood TopLevelFlag
    lvl UsageDetails
    usage [Id]
    bndrs
      = (Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all Id -> Bool
    ok [Id]
    bndrs  -- Invariant 3: Either all are join points or none are
      where
        ok :: Id -> Bool
    ok Id
    bndr = TopLevelFlag -> Id -> TailCallInfo -> Bool
    okForJoinPoint TopLevelFlag
    lvl Id
    bndr (UsageDetails -> Id -> TailCallInfo
    lookupTailCallInfo UsageDetails
    usage Id
    bndr)

    okForJoinPoint :: TopLevelFlag -> Id -> TailCallInfo -> Bool
        -- See Note [Invariants on join points]; invariants cited by number below.
        -- Invariant 2 is always satisfiable by the simplifier by eta expansion.
    okForJoinPoint :: TopLevelFlag -> Id -> TailCallInfo -> Bool
    okForJoinPoint TopLevelFlag
    lvl Id
    bndr TailCallInfo
    tail_call_info
      | Id -> Bool
    isJoinId Id
    bndr        -- A current join point should still be one!
      = Bool -> String -> SDoc -> Bool -> Bool
    forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
    warnPprTrace Bool
    lost_join String
    "Lost join point" SDoc
    lost_join_doc (Bool -> Bool) -> Bool -> Bool
    forall a b. (a -> b) -> a -> b
    $
        Bool
    True
      | Bool
    valid_join
      = Bool
    True
      | Bool
    otherwise
      = Bool
    False
      where
        valid_join :: Bool
    valid_join | TopLevelFlag
    NotTopLevel <- TopLevelFlag
    lvl
                   , AlwaysTailCalled JoinArity
    arity <- TailCallInfo
    tail_call_info

                   , -- Invariant 1 as applied to LHSes of rules
                     (CoreRule -> Bool) -> [CoreRule] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all (JoinArity -> CoreRule -> Bool
    ok_rule JoinArity
    arity) (Id -> [CoreRule]
    idCoreRules Id
    bndr)

                     -- Invariant 2a: stable unfoldings
                      -- See Note [Join points and INLINE pragmas]
                   , JoinArity -> Unfolding -> Bool
    ok_unfolding JoinArity
    arity (IdUnfoldingFun
    realIdUnfolding Id
    bndr)

                     -- Invariant 4: Satisfies polymorphism rule
                   , JoinArity -> Type -> Bool
    isValidJoinPointType JoinArity
    arity (Id -> Type
    idType Id
    bndr)
                   = Bool
    True
                   | Bool
    otherwise
                   = Bool
    False

        lost_join :: Bool
    lost_join | JoinPoint JoinArity
    ja <- Id -> JoinPointHood
    idJoinPointHood Id
    bndr
                  = Bool -> Bool
    not Bool
    valid_join Bool -> Bool -> Bool
    ||
                    (case TailCallInfo
    tail_call_info of  -- Valid join but arity differs
                       AlwaysTailCalled JoinArity
    ja' -> JoinArity
    ja JoinArity -> JoinArity -> Bool
    forall a. Eq a => a -> a -> Bool
    /= JoinArity
    ja'
                       TailCallInfo
    _                    -> Bool
    False)
                  | Bool
    otherwise = Bool
    False

        ok_rule :: JoinArity -> CoreRule -> Bool
    ok_rule JoinArity
    _ BuiltinRule{} = Bool
    False -- only possible with plugin shenanigans
        ok_rule JoinArity
    join_arity (Rule { ru_args :: CoreRule -> [CoreExpr]
    ru_args = [CoreExpr]
    args })
          = [CoreExpr]
    args [CoreExpr] -> JoinArity -> Bool
    forall a. [a] -> JoinArity -> Bool
    `lengthIs` JoinArity
    join_arity
            -- Invariant 1 as applied to LHSes of rules

        -- ok_unfolding returns False if we should /not/ convert a non-join-id
        -- into a join-id, even though it is AlwaysTailCalled
        ok_unfolding :: JoinArity -> Unfolding -> Bool
    ok_unfolding JoinArity
    join_arity (CoreUnfolding { uf_src :: Unfolding -> UnfoldingSource
    uf_src = UnfoldingSource
    src, uf_tmpl :: Unfolding -> CoreExpr
    uf_tmpl = CoreExpr
    rhs })
          = Bool -> Bool
    not (UnfoldingSource -> Bool
    isStableSource UnfoldingSource
    src Bool -> Bool -> Bool
    && JoinArity
    join_arity JoinArity -> JoinArity -> Bool
    forall a. Ord a => a -> a -> Bool
    > CoreExpr -> JoinArity
    joinRhsArity CoreExpr
    rhs)
        ok_unfolding JoinArity
    _ (DFunUnfolding {})
          = Bool
    False
        ok_unfolding JoinArity
    _ Unfolding
    _
          = Bool
    True

        lost_join_doc :: SDoc
    lost_join_doc
          = [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "bndr:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    bndr
                 , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "tc:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> TailCallInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr TailCallInfo
    tail_call_info
                 , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "rules:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [CoreRule] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Id -> [CoreRule]
    idCoreRules Id
    bndr)
                 , case TailCallInfo
    tail_call_info of
                     AlwaysTailCalled JoinArity
    arity ->
                        [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ok_unf:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Bool -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (JoinArity -> Unfolding -> Bool
    ok_unfolding JoinArity
    arity (IdUnfoldingFun
    realIdUnfolding Id
    bndr))
                             , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "ok_type:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Bool -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (JoinArity -> Type -> Bool
    isValidJoinPointType JoinArity
    arity (Id -> Type
    idType Id
    bndr)) ]
                     TailCallInfo
    _ -> SDoc
    forall doc. IsOutput doc => doc
    empty ]

    {- Note [Join points and INLINE pragmas]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       f x = let g = \x. not  -- Arity 1
                 {-# INLINE g #-}
             in case x of
                  A -> g True True
                  B -> g True False
                  C -> blah2

    Here 'g' is always tail-called applied to 2 args, but the stable
    unfolding captured by the INLINE pragma has arity 1.  If we try to
    convert g to be a join point, its unfolding will still have arity 1
    (since it is stable, and we don't meddle with stable unfoldings), and
    Lint will complain (see Note [Invariants on join points], (2a), in
    GHC.Core.  #13413.

    Moreover, since g is going to be inlined anyway, there is no benefit
    from making it a join point.

    If it is recursive, and uselessly marked INLINE, this will stop us
    making it a join point, which is annoying.  But occasionally
    (notably in class methods; see Note [Instances and loop breakers] in
    GHC.Tc.TyCl.Instance) we mark recursive things as INLINE but the recursion
    unravels; so ignoring INLINE pragmas on recursive things isn't good
    either.

    See Invariant 2a of Note [Invariants on join points] in GHC.Core

    ************************************************************************
    *                                                                      *
    \subsection{Operations over OccInfo}
    *                                                                      *
    ************************************************************************
    -}

    markNonTail :: OccInfo -> OccInfo
    markNonTail :: OccInfo -> OccInfo
    markNonTail OccInfo
    IAmDead = OccInfo
    IAmDead
    markNonTail OccInfo
    occ     = OccInfo
    occ { occ_tail = NoTailCallInfo }

    andLocalOcc :: LocalOcc -> LocalOcc -> LocalOcc
    andLocalOcc :: LocalOcc -> LocalOcc -> LocalOcc
    andLocalOcc LocalOcc
    occ1 LocalOcc
    occ2 = TailCallInfo -> LocalOcc
    ManyOccL (TailCallInfo
    tci1 TailCallInfo -> TailCallInfo -> TailCallInfo
    `andTailCallInfo` TailCallInfo
    tci2)
      where
        !tci1 :: TailCallInfo
    tci1 = LocalOcc -> TailCallInfo
    localTailCallInfo LocalOcc
    occ1
        !tci2 :: TailCallInfo
    tci2 = LocalOcc -> TailCallInfo
    localTailCallInfo LocalOcc
    occ2

    orLocalOcc :: LocalOcc -> LocalOcc -> LocalOcc
    -- (orLocalOcc occ1 occ2) is used
    -- when combining occurrence info from branches of a case
    orLocalOcc :: LocalOcc -> LocalOcc -> LocalOcc
    orLocalOcc (OneOccL { lo_n_br :: LocalOcc -> JoinArity
    lo_n_br = JoinArity
    nbr1, lo_int_cxt :: LocalOcc -> InterestingCxt
    lo_int_cxt = InterestingCxt
    int_cxt1, lo_tail :: LocalOcc -> TailCallInfo
    lo_tail = TailCallInfo
    tci1 })
               (OneOccL { lo_n_br :: LocalOcc -> JoinArity
    lo_n_br = JoinArity
    nbr2, lo_int_cxt :: LocalOcc -> InterestingCxt
    lo_int_cxt = InterestingCxt
    int_cxt2, lo_tail :: LocalOcc -> TailCallInfo
    lo_tail = TailCallInfo
    tci2 })
      = OneOccL { lo_n_br :: JoinArity
    lo_n_br    = JoinArity
    nbr1 JoinArity -> JoinArity -> JoinArity
    forall a. Num a => a -> a -> a
    + JoinArity
    nbr2
                , lo_int_cxt :: InterestingCxt
    lo_int_cxt = InterestingCxt
    int_cxt1 InterestingCxt -> InterestingCxt -> InterestingCxt
    forall a. Monoid a => a -> a -> a
    `mappend` InterestingCxt
    int_cxt2
                , lo_tail :: TailCallInfo
    lo_tail    = TailCallInfo
    tci1 TailCallInfo -> TailCallInfo -> TailCallInfo
    `andTailCallInfo` TailCallInfo
    tci2 }
    orLocalOcc LocalOcc
    occ1 LocalOcc
    occ2 = LocalOcc -> LocalOcc -> LocalOcc
    andLocalOcc LocalOcc
    occ1 LocalOcc
    occ2

    andTailCallInfo :: TailCallInfo -> TailCallInfo -> TailCallInfo
    andTailCallInfo :: TailCallInfo -> TailCallInfo -> TailCallInfo
    andTailCallInfo info :: TailCallInfo
    info@(AlwaysTailCalled JoinArity
    arity1) (AlwaysTailCalled JoinArity
    arity2)
      | JoinArity
    arity1 JoinArity -> JoinArity -> Bool
    forall a. Eq a => a -> a -> Bool
    == JoinArity
    arity2 = TailCallInfo
    info
    andTailCallInfo TailCallInfo
    _ TailCallInfo
    _  = TailCallInfo
    NoTailCallInfo