    {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}

    {-
    (c) The GRASP/AQUA Project, Glasgow University, 1993-1998

    \section[Specialise]{Stamping out overloading, and (optionally) polymorphism}
    -}

    module GHC.Core.Opt.Specialise ( specProgram, specUnfolding ) where

    import GHC.Prelude

    import GHC.Driver.DynFlags
    import GHC.Driver.Config
    import GHC.Driver.Config.Diagnostic
    import GHC.Driver.Config.Core.Rules ( initRuleOpts )

    import GHC.Core.Type  hiding( substTy, substCo, extendTvSubst, zapSubst )
    import GHC.Core.Multiplicity
    import GHC.Core.SimpleOpt( defaultSimpleOpts, simpleOptExprWith )
    import GHC.Core.Predicate
    import GHC.Core.Coercion( Coercion )
    import GHC.Core.Opt.Monad
    import qualified GHC.Core.Subst as Core
    import GHC.Core.Unfold.Make
    import GHC.Core
    import GHC.Core.Make      ( mkLitRubbish )
    import GHC.Core.Unify     ( tcMatchTy )
    import GHC.Core.Rules
    import GHC.Core.Utils     ( exprIsTrivial, exprIsTopLevelBindable
                              , mkCast, exprType
                              , stripTicksTop, mkInScopeSetBndrs )
    import GHC.Core.FVs
    import GHC.Core.TyCo.FVs ( tyCoVarsOfTypeList )
    import GHC.Core.Opt.Arity( collectBindersPushingCo )
    -- import GHC.Core.Ppr( pprIds )

    import GHC.Builtin.Types  ( unboxedUnitTy )

    import GHC.Data.Maybe     ( maybeToList, isJust )
    import GHC.Data.Bag
    import GHC.Data.OrdList
    import GHC.Data.List.SetOps

    import GHC.Types.Basic
    import GHC.Types.Unique.Supply
    import GHC.Types.Unique.DFM
    import GHC.Types.Name
    import GHC.Types.Tickish
    import GHC.Types.Id.Make  ( voidArgId, voidPrimId )
    import GHC.Types.Var      ( PiTyBinder(..), isLocalVar, isInvisibleFunArg, mkLocalVar )
    import GHC.Types.Var.Set
    import GHC.Types.Var.Env
    import GHC.Types.Id
    import GHC.Types.Id.Info
    import GHC.Types.Error

    import GHC.Utils.Error ( mkMCDiagnostic )
    import GHC.Utils.Monad    ( foldlM )
    import GHC.Utils.Misc
    import GHC.Utils.Outputable
    import GHC.Utils.Panic

    import GHC.Unit.Module( Module )
    import GHC.Unit.Module.ModGuts
    import GHC.Core.Unfold

    import Data.List( partition )
    import Data.List.NonEmpty ( NonEmpty (..) )
    import GHC.Core.Subst (substTickish)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[notes-Specialise]{Implementation notes [SLPJ, Aug 18 1993]}
    *                                                                      *
    ************************************************************************

    These notes describe how we implement specialisation to eliminate
    overloading.

    The specialisation pass works on Core
    syntax, complete with all the explicit dictionary application,
    abstraction and construction as added by the type checker.  The
    existing type checker remains largely as it is.

    One important thought: the {\em types} passed to an overloaded
    function, and the {\em dictionaries} passed are mutually redundant.
    If the same function is applied to the same type(s) then it is sure to
    be applied to the same dictionary(s)---or rather to the same {\em
    values}.  (The arguments might look different but they will evaluate
    to the same value.)

    Second important thought: we know that we can make progress by
    treating dictionary arguments as static and worth specialising on.  So
    we can do without binding-time analysis, and instead specialise on
    dictionary arguments and no others.

    The basic idea
    ~~~~~~~~~~~~~~
    Suppose we have

            let f = <f_rhs>
            in <body>

    and suppose f is overloaded.

    STEP 1: CALL-INSTANCE COLLECTION

    We traverse <body>, accumulating all applications of f to types and
    dictionaries.

    (Might there be partial applications, to just some of its types and
    dictionaries?  In principle yes, but in practice the type checker only
    builds applications of f to all its types and dictionaries, so partial
    applications could only arise as a result of transformation, and even
    then I think it's unlikely.  In any case, we simply don't accumulate such
    partial applications.)

    STEP 2: EQUIVALENCES

    So now we have a collection of calls to f:
            f t1 t2 d1 d2
            f t3 t4 d3 d4
            ...
    Notice that f may take several type arguments.  To avoid ambiguity, we
    say that f is called at type t1/t2 and t3/t4.

    We take equivalence classes using equality of the *types* (ignoring
    the dictionary args, which as mentioned previously are redundant).

    STEP 3: SPECIALISATION

    For each equivalence class, choose a representative (f t1 t2 d1 d2),
    and create a local instance of f, defined thus:

            f@t1/t2 = <f_rhs> t1 t2 d1 d2

    f_rhs presumably has some big lambdas and dictionary lambdas, so lots
    of simplification will now result.  However we don't actually *do* that
    simplification.  Rather, we leave it for the simplifier to do.  If we
    *did* do it, though, we'd get more call instances from the specialised
    RHS.  We can work out what they are by instantiating the call-instance
    set from f's RHS with the types t1, t2.

    Add this new id to f's IdInfo, to record that f has a specialised version.

    Before doing any of this, check that f's IdInfo doesn't already
    tell us about an existing instance of f at the required type/s.
    (This might happen if specialisation was applied more than once, or
    it might arise from user SPECIALIZE pragmas.)

    Recursion
    ~~~~~~~~~
    Wait a minute!  What if f is recursive?  Then we can't just plug in
    its right-hand side, can we?

    But it's ok.  The type checker *always* creates non-recursive definitions
    for overloaded recursive functions.  For example:

            f x = f (x+x)           -- Yes I know its silly

    becomes

            f a (d::Num a) = let p = +.sel a d
                             in
                             letrec fl (y::a) = fl (p y y)
                             in
                             fl

    We still have recursion for non-overloaded functions which we
    specialise, but the recursive call should get specialised to the
    same recursive version.

    Polymorphism 1
    ~~~~~~~~~~~~~~

    All this is crystal clear when the function is applied to *constant
    types*; that is, types which have no type variables inside.  But what if
    it is applied to non-constant types?  Suppose we find a call of f at type
    t1/t2.  There are two possibilities:

    (a) The free type variables of t1, t2 are in scope at the definition point
    of f.  In this case there's no problem, we proceed just as before.  A common
    example is as follows.  Here's the Haskell:

            g y = let f x = x+x
                  in f y + f y

    After typechecking we have

            g a (d::Num a) (y::a) = let f b (d'::Num b) (x::b) = +.sel b d' x x
                                    in +.sel a d (f a d y) (f a d y)

    Notice that the call to f is at type type "a"; a non-constant type.
    Both calls to f are at the same type, so we can specialise to give:

            g a (d::Num a) (y::a) = let f@a (x::a) = +.sel a d x x
                                    in +.sel a d (f@a y) (f@a y)

    (b) The other case is when the type variables in the instance types
    are *not* in scope at the definition point of f.  The example we are
    working with above is a good case.  There are two instances of (+.sel a d),
    but "a" is not in scope at the definition of +.sel.  Can we do anything?
    Yes, we can "common them up", a sort of limited common sub-expression deal.
    This would give:

            g a (d::Num a) (y::a) = let +.sel@a = +.sel a d
                                        f@a (x::a) = +.sel@a x x
                                    in +.sel@a (f@a y) (f@a y)

    This can save work, and can't be spotted by the type checker, because
    the two instances of +.sel weren't originally at the same type.

    Further notes on (b)

    * There are quite a few variations here.  For example, the defn of
      +.sel could be floated outside the \y, to attempt to gain laziness.
      It certainly mustn't be floated outside the \d because the d has to
      be in scope too.

    * We don't want to inline f_rhs in this case, because
    that will duplicate code.  Just commoning up the call is the point.

    * Nothing gets added to +.sel's IdInfo.

    * Don't bother unless the equivalence class has more than one item!

    Not clear whether this is all worth it.  It is of course OK to
    simply discard call-instances when passing a big lambda.

    Polymorphism 2 -- Overloading
    ~~~~~~~~~~~~~~
    Consider a function whose most general type is

            f :: forall a b. Ord a => [a] -> b -> b

    There is really no point in making a version of g at Int/Int and another
    at Int/Bool, because it's only instantiating the type variable "a" which
    buys us any efficiency. Since g is completely polymorphic in b there
    ain't much point in making separate versions of g for the different
    b types.

    That suggests that we should identify which of g's type variables
    are constrained (like "a") and which are unconstrained (like "b").
    Then when taking equivalence classes in STEP 2, we ignore the type args
    corresponding to unconstrained type variable.  In STEP 3 we make
    polymorphic versions.  Thus:

            f@t1/ = /\b -> <f_rhs> t1 b d1 d2

    We do this.

    Dictionary floating
    ~~~~~~~~~~~~~~~~~~~
    Consider this

            f a (d::Num a) = let g = ...
                             in
                             ...(let d1::Ord a = Num.Ord.sel a d in g a d1)...

    Here, g is only called at one type, but the dictionary isn't in scope at the
    definition point for g.  Usually the type checker would build a
    definition for d1 which enclosed g, but the transformation system
    might have moved d1's defn inward.  Solution: float dictionary bindings
    outwards along with call instances.

    Consider

            f x = let g p q = p==q
                      h r s = (r+s, g r s)
                  in
                  h x x

    Before specialisation, leaving out type abstractions we have

            f df x = let g :: Eq a => a -> a -> Bool
                         g dg p q = == dg p q
                         h :: Num a => a -> a -> (a, Bool)
                         h dh r s = let deq = eqFromNum dh
                                    in (+ dh r s, g deq r s)
                  in
                  h df x x

    After specialising h we get a specialised version of h, like this:

                        h' r s = let deq = eqFromNum df
                                 in (+ df r s, g deq r s)

    But we can't naively make an instance for g from this, because deq is not in scope
    at the defn of g.  Instead, we have to float out the (new) defn of deq
    to widen its scope.  Notice that this floating can't be done in advance -- it only
    shows up when specialisation is done.

    User SPECIALIZE pragmas
    ~~~~~~~~~~~~~~~~~~~~~~~
    Specialisation pragmas can be digested by the type checker, and implemented
    by adding extra definitions along with that of f, in the same way as before

            f@t1/t2 = <f_rhs> t1 t2 d1 d2

    Indeed the pragmas *have* to be dealt with by the type checker, because
    only it knows how to build the dictionaries d1 and d2!  For example

            g :: Ord a => [a] -> [a]
            {-# SPECIALIZE f :: [Tree Int] -> [Tree Int] #-}

    Here, the specialised version of g is an application of g's rhs to the
    Ord dictionary for (Tree Int), which only the type checker can conjure
    up.  There might not even *be* one, if (Tree Int) is not an instance of
    Ord!  (All the other specialisation has suitable dictionaries to hand
    from actual calls.)

    Problem.  The type checker doesn't have to hand a convenient <f_rhs>, because
    it is buried in a complex (as-yet-un-desugared) binding group.
    Maybe we should say

            f@t1/t2 = f* t1 t2 d1 d2

    where f* is the Id f with an IdInfo which says "inline me regardless!".
    Indeed all the specialisation could be done in this way.
    That in turn means that the simplifier has to be prepared to inline absolutely
    any in-scope let-bound thing.

    Again, the pragma should permit polymorphism in unconstrained variables:

            h :: Ord a => [a] -> b -> b
            {-# SPECIALIZE h :: [Int] -> b -> b #-}

    We *insist* that all overloaded type variables are specialised to ground types,
    (and hence there can be no context inside a SPECIALIZE pragma).
    We *permit* unconstrained type variables to be specialised to
            - a ground type
            - or left as a polymorphic type variable
    but nothing in between.  So

            {-# SPECIALIZE h :: [Int] -> [c] -> [c] #-}

    is *illegal*.  (It can be handled, but it adds complication, and gains the
    programmer nothing.)

    SPECIALISING INSTANCE DECLARATIONS
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider

            instance Foo a => Foo [a] where
                    ...
            {-# SPECIALIZE instance Foo [Int] #-}

    The original instance decl creates a dictionary-function
    definition:

            dfun.Foo.List :: forall a. Foo a -> Foo [a]

    The SPECIALIZE pragma just makes a specialised copy, just as for
    ordinary function definitions:

            dfun.Foo.List@Int :: Foo [Int]
            dfun.Foo.List@Int = dfun.Foo.List Int dFooInt

    The information about what instance of the dfun exist gets added to
    the dfun's IdInfo in the same way as a user-defined function too.

    Automatic instance decl specialisation?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Can instance decls be specialised automatically?  It's tricky.
    We could collect call-instance information for each dfun, but
    then when we specialised their bodies we'd get new call-instances
    for ordinary functions; and when we specialised their bodies, we might get
    new call-instances of the dfuns, and so on.  This all arises because of
    the unrestricted mutual recursion between instance decls and value decls.

    Still, there's no actual problem; it just means that we may not do all
    the specialisation we could theoretically do.

    Furthermore, instance decls are usually exported and used non-locally,
    so we'll want to compile enough to get those specialisations done.

    Lastly, there's no such thing as a local instance decl, so we can
    survive solely by spitting out *usage* information, and then reading that
    back in as a pragma when next compiling the file.  So for now,
    we only specialise instance decls in response to pragmas.

    SPITTING OUT USAGE INFORMATION
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    To spit out usage information we need to traverse the code collecting
    call-instance information for all imported (non-prelude?) functions
    and data types. Then we equivalence-class it and spit it out.

    This is done at the top-level when all the call instances which escape
    must be for imported functions and data types.

    *** Not currently done ***

    Partial specialisation by pragmas
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    What about partial specialisation:

            k :: (Ord a, Eq b) => [a] -> b -> b -> [a]
            {-# SPECIALIZE k :: Eq b => [Int] -> b -> b -> [a] #-}

    or even

            {-# SPECIALIZE k :: Eq b => [Int] -> [b] -> [b] -> [a] #-}

    Seems quite reasonable.  Similar things could be done with instance decls:

            instance (Foo a, Foo b) => Foo (a,b) where
                    ...
            {-# SPECIALIZE instance Foo a => Foo (a,Int) #-}
            {-# SPECIALIZE instance Foo b => Foo (Int,b) #-}

    Ho hum.  Things are complex enough without this.  I pass.

    Requirements for the simplifier
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The simplifier has to be able to take advantage of the specialisation.

    * When the simplifier finds an application of a polymorphic f, it looks in
    f's IdInfo in case there is a suitable instance to call instead.  This converts

            f t1 t2 d1 d2   ===>   f_t1_t2

    Note that the dictionaries get eaten up too!

    * Dictionary selection operations on constant dictionaries must be
      short-circuited:

            +.sel Int d     ===>  +Int

    The obvious way to do this is in the same way as other specialised
    calls: +.sel has inside it some IdInfo which tells that if it's applied
    to the type Int then it should eat a dictionary and transform to +Int.

    In short, dictionary selectors need IdInfo inside them for constant
    methods.

    * Exactly the same applies if a superclass dictionary is being
      extracted:

            Eq.sel Int d   ===>   dEqInt

    * Something similar applies to dictionary construction too.  Suppose
    dfun.Eq.List is the function taking a dictionary for (Eq a) to
    one for (Eq [a]).  Then we want

            dfun.Eq.List Int d      ===> dEq.List_Int

    Where does the Eq [Int] dictionary come from?  It is built in
    response to a SPECIALIZE pragma on the Eq [a] instance decl.

    In short, dfun Ids need IdInfo with a specialisation for each
    constant instance of their instance declaration.

    All this uses a single mechanism: the SpecEnv inside an Id

    What does the specialisation IdInfo look like?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The SpecEnv of an Id maps a list of types (the template) to an expression

            [Type]  |->  Expr

    For example, if f has this RuleInfo:

            [Int, a]  ->  \d:Ord Int. f' a

    it means that we can replace the call

            f Int t  ===>  (\d. f' t)

    This chucks one dictionary away and proceeds with the
    specialised version of f, namely f'.

    What can't be done this way?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    There is no way, post-typechecker, to get a dictionary for (say)
    Eq a from a dictionary for Eq [a].  So if we find

            ==.sel [t] d

    we can't transform to

            eqList (==.sel t d')

    where
            eqList :: (a->a->Bool) -> [a] -> [a] -> Bool

    Of course, we currently have no way to automatically derive
    eqList, nor to connect it to the Eq [a] instance decl, but you
    can imagine that it might somehow be possible.  Taking advantage
    of this is permanently ruled out.

    Still, this is no great hardship, because we intend to eliminate
    overloading altogether anyway!

    A note about non-tyvar dictionaries
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Some Ids have types like

            forall a,b,c. Eq a -> Ord [a] -> tau

    This seems curious at first, because we usually only have dictionary
    args whose types are of the form (C a) where a is a type variable.
    But this doesn't hold for the functions arising from instance decls,
    which sometimes get arguments with types of form (C (T a)) for some
    type constructor T.

    Should we specialise wrt this compound-type dictionary?  We used to say
    "no", saying:
            "This is a heuristic judgement, as indeed is the fact that we
            specialise wrt only dictionaries.  We choose *not* to specialise
            wrt compound dictionaries because at the moment the only place
            they show up is in instance decls, where they are simply plugged
            into a returned dictionary.  So nothing is gained by specialising
            wrt them."

    But it is simpler and more uniform to specialise wrt these dicts too;
    and in future GHC is likely to support full fledged type signatures
    like
            f :: Eq [(a,b)] => ...

    Note [Specialisation and overlapping instances]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Here is at tricky case (see a comment in MR !8916):

        module A where
          class C a where
            meth :: a -> String
          instance {-# OVERLAPPABLE #-} C (Maybe a) where
            meth _ = "Maybe"

          {-# SPECIALISE f :: Maybe a -> Bool -> String #-}
          f :: C a => a -> Bool -> String
          f a True = f a False
          f a _    = meth a

        module B where
          import A

          instance C (Maybe Int) where
            meth _ = "Int"

          main = putStrLn $ f (Just 42 :: Maybe Int) True

    Running main without optimisations yields "Int", the correct answer.
    Activating optimisations yields "Maybe" due to a rewrite rule in module
    A generated by the SPECIALISE pragma:

        RULE "USPEC f" forall a (d :: C a). f @a d = $sf

    In B we get the call (f @(Maybe Int) (d :: C (Maybe Int))), and
    that rewrites to $sf, but that isn't really right.

    Overlapping instances mean that `C (Maybe Int)` is not a singleton
    type: there two distinct dictionaries that have this type.  And that
    spells trouble for specialistion, which really asssumes singleton
    types.

    For now, we just accept this problem, but it may bite us one day.
    One solution would be to decline to expose any specialisation rules
    to an importing module -- but that seems a bit drastic.

    ************************************************************************
    *                                                                      *
    \subsubsection{The new specialiser}
    *                                                                      *
    ************************************************************************

    Our basic game plan is this.  For let(rec) bound function
            f :: (C a, D c) => (a,b,c,d) -> Bool

    * Find any specialised calls of f, (f ts ds), where
      ts are the type arguments t1 .. t4, and
      ds are the dictionary arguments d1 .. d2.

    * Add a new definition for f1 (say):

            f1 = /\ b d -> (..body of f..) t1 b t3 d d1 d2

      Note that we abstract over the unconstrained type arguments.

    * Add the mapping

            [t1,b,t3,d]  |->  \d1 d2 -> f1 b d

      to the specialisations of f.  This will be used by the
      simplifier to replace calls
                    (f t1 t2 t3 t4) da db
      by
                    (\d1 d1 -> f1 t2 t4) da db

      All the stuff about how many dictionaries to discard, and what types
      to apply the specialised function to, are handled by the fact that the
      SpecEnv contains a template for the result of the specialisation.

    We don't build *partial* specialisations for f.  For example:

      f :: Eq a => a -> a -> Bool
      {-# SPECIALISE f :: (Eq b, Eq c) => (b,c) -> (b,c) -> Bool #-}

    Here, little is gained by making a specialised copy of f.
    There's a distinct danger that the specialised version would
    first build a dictionary for (Eq b, Eq c), and then select the (==)
    method from it!  Even if it didn't, not a great deal is saved.

    We do, however, generate polymorphic, but not overloaded, specialisations:

      f :: Eq a => [a] -> b -> b -> b
      ... SPECIALISE f :: [Int] -> b -> b -> b ...

    Hence, the invariant is this:

            *** no specialised version is overloaded ***

    ************************************************************************
    *                                                                      *
    \subsubsection{The exported function}
    *                                                                      *
    ************************************************************************
    -}

    -- | Specialise calls to type-class overloaded functions occurring in a program.
    specProgram :: ModGuts -> CoreM ModGuts
    specProgram :: ModGuts -> CoreM ModGuts
    specProgram guts :: ModGuts
    guts@(ModGuts { mg_module :: ModGuts -> Module
    mg_module = Module
    this_mod
                              , mg_rules :: ModGuts -> [CoreRule]
    mg_rules  = [CoreRule]
    local_rules
                              , mg_binds :: ModGuts -> CoreProgram
    mg_binds  = CoreProgram
    binds })
      = do { dflags   <- CoreM DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags
           ; rule_env <- initRuleEnv guts
                         -- See Note [Fire rules in the specialiser]

                  -- We need to start with a Subst that knows all the things
                  -- that are in scope, so that the substitution engine doesn't
                  -- accidentally re-use a unique that's already in use
                  -- Easiest thing is to do it all at once, as if all the top-level
                  -- decls were mutually recursive
           ; let top_env = SE { se_subst :: Subst
    se_subst = InScopeSet -> Subst
    Core.mkEmptySubst (InScopeSet -> Subst) -> InScopeSet -> Subst
    forall a b. (a -> b) -> a -> b
    $
                                            CoreProgram -> InScopeSet
    mkInScopeSetBndrs CoreProgram
    binds
                                          --    mkInScopeSetList $
                                          --  bindersOfBinds binds
                              , se_module :: Module
    se_module = Module
    this_mod
                              , se_rules :: RuleEnv
    se_rules  = RuleEnv
    rule_env
                              , se_dflags :: DynFlags
    se_dflags = DynFlags
    dflags }

                 go []           = (CoreProgram, UsageDetails) -> SpecM (CoreProgram, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    emptyUDs)
                 go (InBind
    bind:CoreProgram
    binds) = do (bind', binds', uds') <- TopLevelFlag
    -> SpecEnv
    -> InBind
    -> (SpecEnv -> SpecM (CoreProgram, UsageDetails))
    -> SpecM (CoreProgram, CoreProgram, UsageDetails)
    forall body.
    TopLevelFlag
    -> SpecEnv
    -> InBind
    -> (SpecEnv -> SpecM (body, UsageDetails))
    -> SpecM (CoreProgram, body, UsageDetails)
    specBind TopLevelFlag
    TopLevel SpecEnv
    top_env InBind
    bind ((SpecEnv -> SpecM (CoreProgram, UsageDetails))
     -> SpecM (CoreProgram, CoreProgram, UsageDetails))
    -> (SpecEnv -> SpecM (CoreProgram, UsageDetails))
    -> SpecM (CoreProgram, CoreProgram, UsageDetails)
    forall a b. (a -> b) -> a -> b
    $ \SpecEnv
    _ ->
                                                               CoreProgram -> SpecM (CoreProgram, UsageDetails)
    go CoreProgram
    binds
                                      return (bind' ++ binds', uds')

                 -- Specialise the bindings of this module
           ; (binds', uds) <- runSpecM (go binds)

           ; (spec_rules, spec_binds) <- specImports top_env uds

           ; return (guts { mg_binds = spec_binds ++ binds'
                          , mg_rules = spec_rules ++ local_rules }) }

    {-
    Note [Wrap bindings returned by specImports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    'specImports' returns a set of specialized bindings. However, these are lacking
    necessary floated dictionary bindings, which are returned by
    UsageDetails(ud_binds). These dictionaries need to be brought into scope with
    'wrapDictBinds' before the bindings returned by 'specImports' can be used. See,
    for instance, the 'specImports' call in 'specProgram'.

    Note [Disabling cross-module specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Since GHC 7.10 we have performed specialisation of INLINABLE bindings living
    in modules outside of the current module. This can sometimes uncover user code
    which explodes in size when aggressively optimized. The
    -fno-cross-module-specialise option was introduced to allow users to being
    bitten by such instances to revert to the pre-7.10 behavior.

    See #10491
    -}

    {- *********************************************************************
    *                                                                      *
                       Specialising imported functions
    *                                                                      *
    ********************************************************************* -}

    {- Note [Specialising imported functions]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    specImports specialises imported functions, based on calls in this module.

    When -fspecialise-aggressively is on, we specialise any imported
    function for which we have an unfolding.  The
    -fspecialise-aggressively flag is usually off, because we risk lots of
    orphan modules from over-vigorous specialisation.  (See Note [Orphans]
    in GHC.Core.) However it's not a big deal: anything non-recursive with
    an unfolding-template will probably have been inlined already.

    When -fspecialise-aggressively is off, we are more selective about
    specialisation (see canSpecImport):

    (1) Without -fspecialise-aggressively, do not specialise
        DFunUnfoldings. Note [Do not specialise imported DFuns].

    (2) Without -fspecialise-aggressively, specialise only imported things
        that have a /user-supplied/ INLINE or INLINABLE pragma (hence
        isAnyInlinePragma rather than isStableSource).

        In particular, we don't want to specialise workers created by
        worker/wrapper (for functions with no pragma) because they won't
        specialise usefully, and they generate quite a bit of useless code
        bloat.

        Specialise even INLINE things; it hasn't inlined yet, so perhaps
        it never will.  Moreover it may have calls inside it that we want
        to specialise

    Wrinkle (W1): If we specialise an imported Id M.foo, we make a /local/
    binding $sfoo.  But specImports may further specialise $sfoo. So we end up
    with RULES for both M.foo (imported) and $sfoo (local).  Rules for local
    Ids should be attached to the Ids themselves (see GHC.HsToCore
    Note [Attach rules to local ids]); so we must partition the rules and
    attach the local rules.  That is done in specImports, via addRulesToId.

    Note [Glom the bindings if imported functions are specialised]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we have an imported, *recursive*, INLINABLE function
       f :: Eq a => a -> a
       f = /\a \d x. ...(f a d)...
    In the module being compiled we have
       g x = f (x::Int)
    Now we'll make a specialised function
       f_spec :: Int -> Int
       f_spec = \x -> ...(f Int dInt)...
       {-# RULE  f Int _ = f_spec #-}
       g = \x. f Int dInt x
    Note that f_spec doesn't look recursive
    After rewriting with the RULE, we get
       f_spec = \x -> ...(f_spec)...
    BUT since f_spec was non-recursive before it'll *stay* non-recursive.
    The occurrence analyser never turns a NonRec into a Rec.  So we must
    make sure that f_spec is recursive.  Easiest thing is to make all
    the specialisations for imported bindings recursive.
    -}

    specImports :: SpecEnv
                -> UsageDetails
                -> CoreM ([CoreRule], [CoreBind])
    specImports :: SpecEnv -> UsageDetails -> CoreM ([CoreRule], CoreProgram)
    specImports SpecEnv
    top_env (MkUD { ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    dict_binds, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls })
      | Bool -> Bool
    not (Bool -> Bool) -> Bool -> Bool
    forall a b. (a -> b) -> a -> b
    $ GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_CrossModuleSpecialise (SpecEnv -> DynFlags
    se_dflags SpecEnv
    top_env)
        -- See Note [Disabling cross-module specialisation]
      = ([CoreRule], CoreProgram) -> CoreM ([CoreRule], CoreProgram)
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], FloatedDictBinds -> CoreProgram -> CoreProgram
    wrapDictBinds FloatedDictBinds
    dict_binds [])

      | Bool
    otherwise
      = do { let env_w_dict_bndrs :: SpecEnv
    env_w_dict_bndrs = SpecEnv
    top_env SpecEnv -> FloatedDictBinds -> SpecEnv
    `bringFloatedDictsIntoScope` FloatedDictBinds
    dict_binds
           ; (_env, spec_rules, spec_binds) <- SpecEnv
    -> [Id]
    -> FloatedDictBinds
    -> CallDetails
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    spec_imports SpecEnv
    env_w_dict_bndrs [] FloatedDictBinds
    dict_binds CallDetails
    calls

                 -- Make a Rec: see Note [Glom the bindings if imported functions are specialised]
                 --
                 -- wrapDictBinds: don't forget to wrap the specialized bindings with
                 --   bindings for the needed dictionaries.
                 --   See Note [Wrap bindings returned by specImports]
                 --
                 -- addRulesToId: see Wrinkle (W1) in Note [Specialising imported functions]
                 --               c.f. GHC.HsToCore.addExportFlagsAndRules
           ; let (rules_for_locals, rules_for_imps) = partition isLocalRule spec_rules
                 local_rule_base = RuleBase -> [CoreRule] -> RuleBase
    extendRuleBaseList RuleBase
    emptyRuleBase [CoreRule]
    rules_for_locals
                 final_binds
                   | CoreProgram -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null CoreProgram
    spec_binds = FloatedDictBinds -> CoreProgram -> CoreProgram
    wrapDictBinds FloatedDictBinds
    dict_binds []
                   | Bool
    otherwise       = [[(Id, OutExpr)] -> InBind
    forall b. [(b, Expr b)] -> Bind b
    Rec ([(Id, OutExpr)] -> InBind) -> [(Id, OutExpr)] -> InBind
    forall a b. (a -> b) -> a -> b
    $ (Id -> Id) -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall (f :: * -> *) a c b.
    Functor f =>
    (a -> c) -> f (a, b) -> f (c, b)
    mapFst (RuleBase -> Id -> Id
    addRulesToId RuleBase
    local_rule_base) ([(Id, OutExpr)] -> [(Id, OutExpr)])
    -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a b. (a -> b) -> a -> b
    $
                                              CoreProgram -> [(Id, OutExpr)]
    forall b. [Bind b] -> [(b, Expr b)]
    flattenBinds                          (CoreProgram -> [(Id, OutExpr)]) -> CoreProgram -> [(Id, OutExpr)]
    forall a b. (a -> b) -> a -> b
    $
                                              FloatedDictBinds -> CoreProgram -> CoreProgram
    wrapDictBinds FloatedDictBinds
    dict_binds              (CoreProgram -> CoreProgram) -> CoreProgram -> CoreProgram
    forall a b. (a -> b) -> a -> b
    $
                                              CoreProgram
    spec_binds]

           ; return (rules_for_imps, final_binds)
        }

    -- | Specialise a set of calls to imported bindings
    spec_imports :: SpecEnv          -- Passed in so that all top-level Ids are in scope
                                     ---In-scope set includes the FloatedDictBinds
                 -> [Id]             -- Stack of imported functions being specialised
                                     -- See Note [specImport call stack]
                 -> FloatedDictBinds -- Dict bindings, used /only/ for filterCalls
                                     -- See Note [Avoiding loops in specImports]
                 -> CallDetails      -- Calls for imported things
                 -> CoreM ( SpecEnv      -- Env contains the new rules
                          , [CoreRule]   -- New rules
                          , [CoreBind] ) -- Specialised bindings
    spec_imports :: SpecEnv
    -> [Id]
    -> FloatedDictBinds
    -> CallDetails
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    spec_imports SpecEnv
    env [Id]
    callers FloatedDictBinds
    dict_binds CallDetails
    calls
      = do { let import_calls :: [CallInfoSet]
    import_calls = CallDetails -> [CallInfoSet]
    forall a. DVarEnv a -> [a]
    dVarEnvElts CallDetails
    calls
    --       ; debugTraceMsg (text "specImports {" <+>
    --                         vcat [ text "calls:" <+> ppr import_calls
    --                              , text "dict_binds:" <+> ppr dict_binds ])
           ; (env, rules, spec_binds) <- SpecEnv
    -> [CallInfoSet] -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    go SpecEnv
    env [CallInfoSet]
    import_calls
    --       ; debugTraceMsg (text "End specImports }" <+> ppr import_calls)

           ; return (env, rules, spec_binds) }
      where
        go :: SpecEnv -> [CallInfoSet] -> CoreM (SpecEnv, [CoreRule], [CoreBind])
        go :: SpecEnv
    -> [CallInfoSet] -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    go SpecEnv
    env [] = (SpecEnv, [CoreRule], CoreProgram)
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, [], [])
        go SpecEnv
    env (CallInfoSet
    cis : [CallInfoSet]
    other_calls)
          = do { -- debugTraceMsg (text "specImport {" <+> ppr cis)
               ; (env, rules1, spec_binds1) <- SpecEnv
    -> [Id]
    -> FloatedDictBinds
    -> CallInfoSet
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    spec_import SpecEnv
    env [Id]
    callers FloatedDictBinds
    dict_binds CallInfoSet
    cis
               ; -- debugTraceMsg (text "specImport }" <+> ppr cis)

               ; (env, rules2, spec_binds2) <- go env other_calls
               ; return (env, rules1 ++ rules2, spec_binds1 ++ spec_binds2) }

    spec_import :: SpecEnv               -- Passed in so that all top-level Ids are in scope
                                         ---In-scope set includes the FloatedDictBinds
                -> [Id]                  -- Stack of imported functions being specialised
                                         -- See Note [specImport call stack]
                -> FloatedDictBinds      -- Dict bindings, used /only/ for filterCalls
                                         -- See Note [Avoiding loops in specImports]
                -> CallInfoSet           -- Imported function and calls for it
                -> CoreM ( SpecEnv
                         , [CoreRule]    -- New rules
                         , [CoreBind] )  -- Specialised bindings
    spec_import :: SpecEnv
    -> [Id]
    -> FloatedDictBinds
    -> CallInfoSet
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    spec_import SpecEnv
    env [Id]
    callers FloatedDictBinds
    dict_binds cis :: CallInfoSet
    cis@(CIS Id
    fn Bag CallInfo
    _)
      | String -> Id -> [Id] -> Bool
    forall a. Eq a => String -> a -> [a] -> Bool
    isIn String
    "specImport" Id
    fn [Id]
    callers
      = (SpecEnv, [CoreRule], CoreProgram)
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, [], [])  -- No warning.  This actually happens all the time
                              -- when specialising a recursive function, because
                              -- the RHS of the specialised function contains a recursive
                              -- call to the original function

      | [CallInfo] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [CallInfo]
    good_calls
      = (SpecEnv, [CoreRule], CoreProgram)
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, [], [])

      | Just OutExpr
    rhs <- DynFlags -> Id -> Maybe OutExpr
    canSpecImport DynFlags
    dflags Id
    fn
      = do {     -- Get rules from the external package state
                 -- We keep doing this in case we "page-fault in"
                 -- more rules as we go along
           ; eps_rules <- CoreM RuleBase
    getExternalRuleBase
           ; let rule_env = SpecEnv -> RuleEnv
    se_rules SpecEnv
    env RuleEnv -> RuleBase -> RuleEnv
    `updExternalPackageRules` RuleBase
    eps_rules

    --       ; debugTraceMsg (text "specImport1" <+> vcat
    --           [ text "function:" <+> ppr fn
    --           , text "good calls:" <+> ppr good_calls
    --           , text "existing rules:" <+> ppr (getRules rule_env fn)
    --           , text "rhs:" <+> ppr rhs
    --           , text "dict_binds:" <+> ppr dict_binds ])

           ; (rules1, spec_pairs, MkUD { ud_binds = dict_binds1, ud_calls = new_calls })
                <- runSpecM $ specCalls True env (getRules rule_env fn) good_calls fn rhs

           ; let spec_binds1 = [Id -> OutExpr -> InBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    b OutExpr
    r | (Id
    b,OutExpr
    r) <- [(Id, OutExpr)]
    spec_pairs]
                 -- After the rules kick in, via fireRewriteRules, we may get recursion,
                 -- but we rely on a global GlomBinds to sort that out later
                 -- See Note [Glom the bindings if imported functions are specialised]
                 -- Meanwhile, though, bring the binders into scope

                 new_subst = SpecEnv -> Subst
    se_subst SpecEnv
    env Subst -> [Id] -> Subst
    `Core.extendSubstInScopeList` ((Id, OutExpr) -> Id) -> [(Id, OutExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, OutExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, OutExpr)]
    spec_pairs
                 new_env   = SpecEnv
    env { se_rules = rule_env `addLocalRules` rules1
                                 , se_subst = new_subst }
                             SpecEnv -> FloatedDictBinds -> SpecEnv
    `bringFloatedDictsIntoScope` FloatedDictBinds
    dict_binds1

           -- Now specialise any cascaded calls
    --       ; debugTraceMsg (text "specImport 2" <+> vcat
    --           [ text "function:" <+> ppr fn
    --           , text "rules1:" <+> ppr rules1
    --           , text "spec_binds1" <+> ppr spec_binds1
    --           , text "dict_binds1" <+> ppr dict_binds1
    --           , text "new_calls" <+> ppr new_calls ])

           ; (env, rules2, spec_binds2)
                <- spec_imports new_env (fn:callers)
                                        (dict_binds `thenFDBs` dict_binds1)
                                        new_calls

           ; let final_binds = FloatedDictBinds -> CoreProgram -> CoreProgram
    wrapDictBinds FloatedDictBinds
    dict_binds1 (CoreProgram -> CoreProgram) -> CoreProgram -> CoreProgram
    forall a b. (a -> b) -> a -> b
    $
                               CoreProgram
    spec_binds2 CoreProgram -> CoreProgram -> CoreProgram
    forall a. [a] -> [a] -> [a]
    ++ CoreProgram
    spec_binds1

           ; return (env, rules2 ++ rules1, final_binds) }

      | Bool
    otherwise
      = do { DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    tryWarnMissingSpecs DynFlags
    dflags [Id]
    callers Id
    fn [CallInfo]
    good_calls
           ; (SpecEnv, [CoreRule], CoreProgram)
    -> CoreM (SpecEnv, [CoreRule], CoreProgram)
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, [], [])}

      where
        dflags :: DynFlags
    dflags = SpecEnv -> DynFlags
    se_dflags SpecEnv
    env
        good_calls :: [CallInfo]
    good_calls = CallInfoSet -> FloatedDictBinds -> [CallInfo]
    filterCalls CallInfoSet
    cis FloatedDictBinds
    dict_binds
           -- SUPER IMPORTANT!  Drop calls that (directly or indirectly) refer to fn
           -- See Note [Avoiding loops in specImports]

    canSpecImport :: DynFlags -> Id -> Maybe CoreExpr
    canSpecImport :: DynFlags -> Id -> Maybe OutExpr
    canSpecImport DynFlags
    dflags Id
    fn
      | Id -> Bool
    isDataConWrapId Id
    fn
      = Maybe OutExpr
    forall a. Maybe a
    Nothing   -- Don't specialise data-con wrappers, even if they
                  -- have dict args; there is no benefit.

      | CoreUnfolding { uf_tmpl :: Unfolding -> OutExpr
    uf_tmpl = OutExpr
    rhs } <- Unfolding
    unf
        -- CoreUnfolding: see Note [Specialising imported functions] point (1).
      , InlinePragma -> Bool
    isAnyInlinePragma (Id -> InlinePragma
    idInlinePragma Id
    fn)
        -- See Note [Specialising imported functions] point (2).
      = OutExpr -> Maybe OutExpr
    forall a. a -> Maybe a
    Just OutExpr
    rhs

      | GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_SpecialiseAggressively DynFlags
    dflags
      = Unfolding -> Maybe OutExpr
    maybeUnfoldingTemplate Unfolding
    unf
        -- With -fspecialise-aggressively, specialise anything
        -- with an unfolding, stable or not, DFun or not

      | Bool
    otherwise = Maybe OutExpr
    forall a. Maybe a
    Nothing
      where
        unf :: Unfolding
    unf = Id -> Unfolding
    realIdUnfolding Id
    fn   -- We want to see the unfolding even for loop breakers

    -- | Returns whether or not to show a missed-spec warning.
    -- If -Wall-missed-specializations is on, show the warning.
    -- Otherwise, if -Wmissed-specializations is on, only show a warning
    -- if there is at least one imported function being specialized,
    -- and if all imported functions are marked with an inline pragma
    -- Use the most specific warning as the reason.
    tryWarnMissingSpecs :: DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    -- See Note [Warning about missed specialisations]
    tryWarnMissingSpecs :: DynFlags -> [Id] -> Id -> [CallInfo] -> CoreM ()
    tryWarnMissingSpecs DynFlags
    dflags [Id]
    callers Id
    fn [CallInfo]
    calls_for_fn
      | Id -> Bool
    isClassOpId Id
    fn = () -> CoreM ()
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return () -- See Note [Missed specialisation for ClassOps]
      | WarningFlag -> DynFlags -> Bool
    wopt WarningFlag
    Opt_WarnMissedSpecs DynFlags
    dflags
        Bool -> Bool -> Bool
    && Bool -> Bool
    not ([Id] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    callers)
        Bool -> Bool -> Bool
    && Bool
    allCallersInlined                  = DiagnosticReason -> CoreM ()
    doWarn (DiagnosticReason -> CoreM ()) -> DiagnosticReason -> CoreM ()
    forall a b. (a -> b) -> a -> b
    $ WarningFlag -> DiagnosticReason
    WarningWithFlag WarningFlag
    Opt_WarnMissedSpecs
      | WarningFlag -> DynFlags -> Bool
    wopt WarningFlag
    Opt_WarnAllMissedSpecs DynFlags
    dflags    = DiagnosticReason -> CoreM ()
    doWarn (DiagnosticReason -> CoreM ()) -> DiagnosticReason -> CoreM ()
    forall a b. (a -> b) -> a -> b
    $ WarningFlag -> DiagnosticReason
    WarningWithFlag WarningFlag
    Opt_WarnAllMissedSpecs
      | Bool
    otherwise                             = () -> CoreM ()
    forall a. a -> CoreM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      where
        allCallersInlined :: Bool
    allCallersInlined = (Id -> Bool) -> [Id] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    all (InlinePragma -> Bool
    isAnyInlinePragma (InlinePragma -> Bool) -> (Id -> InlinePragma) -> Id -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Id -> InlinePragma
    idInlinePragma) [Id]
    callers
        diag_opts :: DiagOpts
    diag_opts = DynFlags -> DiagOpts
    initDiagOpts DynFlags
    dflags
        doWarn :: DiagnosticReason -> CoreM ()
    doWarn DiagnosticReason
    reason =
          MessageClass -> SDoc -> CoreM ()
    msg (DiagOpts
    -> DiagnosticReason -> Maybe DiagnosticCode -> MessageClass
    mkMCDiagnostic DiagOpts
    diag_opts DiagnosticReason
    reason Maybe DiagnosticCode
    forall a. Maybe a
    Nothing)
            ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ SDoc -> Int -> SDoc -> SDoc
    hang (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text (String
    "Could not specialise imported function") SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn))
                    Int
    2 ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "when specialising" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    caller)
                            | Id
    caller <- [Id]
    callers])
              , SDoc -> SDoc
    forall doc. IsOutput doc => doc -> doc
    whenPprDebug (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "calls:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat ((CallInfo -> SDoc) -> [CallInfo] -> [SDoc]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id -> CallInfo -> SDoc
    pprCallInfo Id
    fn) [CallInfo]
    calls_for_fn))
              , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "Probable fix: add INLINABLE pragma on" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc -> SDoc
    quotes (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn) ])

    {- Note [Missed specialisation for ClassOps]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In #19592 I saw a number of missed specialisation warnings
    which were the result of things like:

        case isJumpishInstr @X86.Instr $dInstruction_s7f8 eta3_a78C of { ...

    where isJumpishInstr is part of the Instruction class and defined like
    this:

        class Instruction instr where
            ...
            isJumpishInstr :: instr -> Bool
            ...

    isJumpishInstr is a ClassOp which will select the right method
    from within the dictionary via our built in rules. See also
    Note [ClassOp/DFun selection] in GHC.Tc.TyCl.Instance.

    We don't give these unfoldings, and as a result the specialiser
    complains. But usually this doesn't matter. The simplifier will
    apply the rule and we end up with

        case isJumpishInstrImplX86 eta3_a78C of { ...

    Since isJumpishInstrImplX86 is defined for a concrete instance (given
    by the dictionary) it is usually already well specialised!
    Theoretically the implementation of a method could still be overloaded
    over a different type class than what it's a method of. But I wasn't able
    to make this go wrong, and SPJ thinks this should be fine as well.

    So I decided to remove the warnings for failed specialisations on ClassOps
    alltogether as they do more harm than good.
    -}

    {- Note [Do not specialise imported DFuns]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Ticket #18223 shows that specialising calls of DFuns is can cause a huge
    and entirely unnecessary blowup in program size.  Consider a call to
        f @[[[[[[[[T]]]]]]]] d1 x
    where df :: C a => C [a]
          d1 :: C [[[[[[[[T]]]]]]]] = dfC[] @[[[[[[[T]]]]]]] d1
          d2 :: C [[[[[[[T]]]]]]]   = dfC[] @[[[[[[T]]]]]] d3
          ...
    Now we'll specialise f's RHS, which may give rise to calls to 'g',
    also overloaded, which we will specialise, and so on.  However, if
    we specialise the calls to dfC[], we'll generate specialised copies of
    all methods of C, at all types; and the same for C's superclasses.

    And many of these specialised functions will never be called.  We are
    going to call the specialised 'f', and the specialised 'g', but DFuns
    group functions into a tuple, many of whose elements may never be used.

    With deeply-nested types this can lead to a simply overwhelming number
    of specialisations: see #18223 for a simple example (from the wild).
    I measured the number of specialisations for various numbers of calls
    of `flip evalStateT ()`, and got this

                           Size after one simplification
      #calls    #SPEC rules    Terms     Types
          5         56          3100     10600
          9        108         13660     77206

    The real tests case has 60+ calls, which blew GHC out of the water.

    Solution: don't specialise DFuns.  The downside is that if we end
    up with (h (dfun d)), /and/ we don't specialise 'h', then we won't
    pass to 'h' a tuple of specialised functions.

    However, the flag -fspecialise-aggressively (experimental, off by default)
    allows DFuns to specialise as well.

    Note [Avoiding loops in specImports]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We must take great care when specialising instance declarations
    (DFuns like $fOrdList) lest we accidentally build a recursive
    dictionary. See Note [Avoiding loops (DFuns)].

    The basic strategy of Note [Avoiding loops (DFuns)] is to use filterCalls
    to discard loopy specialisations.  But to do that we must ensure
    that the in-scope dict-binds (passed to filterCalls) contains
    all the needed dictionary bindings.  In particular, in the recursive
    call to spec_imports in spec_import, we must include the dict-binds
    from the parent.  Lacking this caused #17151, a really nasty bug.

    Here is what happened.
    * Class structure:
        Source is a superclass of Mut
        Index is a superclass of Source

    * We started with these dict binds
        dSource = $fSourcePix @Int $fIndexInt
        dIndex  = sc_sel dSource
        dMut    = $fMutPix @Int dIndex
      and these calls to specialise
        $fMutPix @Int dIndex
        $fSourcePix @Int $fIndexInt

    * We specialised the call ($fMutPix @Int dIndex)
      ==> new call ($fSourcePix @Int dIndex)
          (because Source is a superclass of Mut)

    * We specialised ($fSourcePix @Int dIndex)
      ==> produces specialised dict $s$fSourcePix,
          a record with dIndex as a field
          plus RULE forall d. ($fSourcePix @Int d) = $s$fSourcePix
      *** This is the bogus step ***

    * Now we decide not to specialise the call
        $fSourcePix @Int $fIndexInt
      because we alredy have a RULE that matches it

    * Finally the simplifer rewrites
        dSource = $fSourcePix @Int $fIndexInt
        ==>  dSource = $s$fSourcePix

    Disaster. Now we have

    Rewrite dSource's RHS to $s$fSourcePix   Disaster
        dSource = $s$fSourcePix
        dIndex  = sc_sel dSource
        $s$fSourcePix = MkSource dIndex ...

    Solution: filterCalls should have stopped the bogus step,
    by seeing that dIndex transitively uses $fSourcePix. But
    it can only do that if it sees all the dict_binds.  Wow.

    --------------
    Here's another example (#13429).  Suppose we have
      class Monoid v => C v a where ...

    We start with a call
       f @ [Integer] @ Integer $fC[]Integer

    Specialising call to 'f' gives dict bindings
       $dMonoid_1 :: Monoid [Integer]
       $dMonoid_1 = M.$p1C @ [Integer] $fC[]Integer

       $dC_1 :: C [Integer] (Node [Integer] Integer)
       $dC_1 = M.$fCvNode @ [Integer] $dMonoid_1

    ...plus a recursive call to
       f @ [Integer] @ (Node [Integer] Integer) $dC_1

    Specialising that call gives
       $dMonoid_2  :: Monoid [Integer]
       $dMonoid_2  = M.$p1C @ [Integer] $dC_1

       $dC_2 :: C [Integer] (Node [Integer] Integer)
       $dC_2 = M.$fCvNode @ [Integer] $dMonoid_2

    Now we have two calls to the imported function
      M.$fCvNode :: Monoid v => C v a
      M.$fCvNode @v @a m = C m some_fun

    But we must /not/ use the call (M.$fCvNode @ [Integer] $dMonoid_2)
    for specialisation, else we get:

      $dC_1 = M.$fCvNode @ [Integer] $dMonoid_1
      $dMonoid_2 = M.$p1C @ [Integer] $dC_1
      $s$fCvNode = C $dMonoid_2 ...
        RULE M.$fCvNode [Integer] _ _ = $s$fCvNode

    Now use the rule to rewrite the call in the RHS of $dC_1
    and we get a loop!

    Note [specImport call stack]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising an imports function 'f', we may get new calls
    of an imported function 'g', which we want to specialise in turn,
    and similarly specialising 'g' might expose a new call to 'h'.

    We track the stack of enclosing functions. So when specialising 'h' we
    have a specImport call stack of [g,f]. We do this for two reasons:
    * Note [Warning about missed specialisations]
    * Note [Avoiding recursive specialisation]

    Note [Warning about missed specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose
     * In module Lib, you carefully mark a function 'foo' INLINABLE
     * Import Lib(foo) into another module M
     * Call 'foo' at some specialised type in M
    Then you jolly well expect it to be specialised in M.  But what if
    'foo' calls another function 'Lib.bar'.  Then you'd like 'bar' to be
    specialised too.  But if 'bar' is not marked INLINABLE it may well
    not be specialised.  The warning Opt_WarnMissedSpecs warns about this.

    It's more noisy to warning about a missed specialisation opportunity
    for /every/ overloaded imported function, but sometimes useful. That
    is what Opt_WarnAllMissedSpecs does.

    ToDo: warn about missed opportunities for local functions.

    Note [Avoiding recursive specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we specialise 'f' we may find new overloaded calls to 'g', 'h' in
    'f's RHS.  So we want to specialise g,h.  But we don't want to
    specialise f any more!  It's possible that f's RHS might have a
    recursive yet-more-specialised call, so we'd diverge in that case.
    And if the call is to the same type, one specialisation is enough.
    Avoiding this recursive specialisation loop is one reason for the
    'callers' stack passed to specImports and specImport.

    ************************************************************************
    *                                                                      *
    \subsubsection{@specExpr@: the main function}
    *                                                                      *
    ************************************************************************
    -}

    data SpecEnv
      = SE { SpecEnv -> Subst
    se_subst :: Core.Subst
                 -- We carry a substitution down:
                 -- a) we must clone any binding that might float outwards,
                 --    to avoid name clashes
                 -- b) we carry a type substitution to use when analysing
                 --    the RHS of specialised bindings (no type-let!)

           , SpecEnv -> Module
    se_module :: Module
           , SpecEnv -> RuleEnv
    se_rules  :: RuleEnv  -- From the home package and this module
           , SpecEnv -> DynFlags
    se_dflags :: DynFlags
         }

    instance Outputable SpecEnv where
      ppr :: SpecEnv -> SDoc
    ppr (SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst })
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SE" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc
    braces (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "subst =" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Subst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Subst
    subst)

    specVar :: SpecEnv -> InId -> SpecM (OutExpr, UsageDetails)
    specVar :: SpecEnv -> Id -> SpecM (OutExpr, UsageDetails)
    specVar env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Core.Subst InScopeSet
    in_scope IdSubstEnv
    ids TvSubstEnv
    _ CvSubstEnv
    _ }) Id
    v
      | Bool -> Bool
    not (Id -> Bool
    isLocalId Id
    v)                   = (OutExpr, UsageDetails) -> SpecM (OutExpr, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    v, UsageDetails
    emptyUDs)
      | Just OutExpr
    e  <- IdSubstEnv -> Id -> Maybe OutExpr
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv IdSubstEnv
    ids       Id
    v = SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr (SpecEnv -> SpecEnv
    zapSubst SpecEnv
    env) OutExpr
    e  -- Note (1)
      | Just Id
    v' <- InScopeSet -> Id -> Maybe Id
    lookupInScope InScopeSet
    in_scope Id
    v = (OutExpr, UsageDetails) -> SpecM (OutExpr, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    v', UsageDetails
    emptyUDs)
      | Bool
    otherwise = String -> SDoc -> SpecM (OutExpr, UsageDetails)
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "specVar" (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    v SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ InScopeSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr InScopeSet
    in_scope)
      -- c.f. GHC.Core.Subst.lookupIdSubst
      -- Note (1): we recurse so we do the lookupInScope thing on any Vars in e
      --           probably has little effect, but it's the right thing.
      --           We need zapSubst because `e` is an OutExpr

    specExpr :: SpecEnv -> CoreExpr -> SpecM (CoreExpr, UsageDetails)

    ---------------- First the easy cases --------------------
    specExpr :: SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env (Var Id
    v)       = SpecEnv -> Id -> SpecM (OutExpr, UsageDetails)
    specVar SpecEnv
    env Id
    v
    specExpr SpecEnv
    env (Type Kind
    ty)     = (OutExpr, UsageDetails) -> SpecM (OutExpr, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Kind -> OutExpr
    forall b. Kind -> Expr b
    Type     (SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env Kind
    ty), UsageDetails
    emptyUDs)
    specExpr SpecEnv
    env (Coercion Coercion
    co) = (OutExpr, UsageDetails) -> SpecM (OutExpr, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Coercion -> OutExpr
    forall b. Coercion -> Expr b
    Coercion (SpecEnv -> Coercion -> Coercion
    substCo SpecEnv
    env Coercion
    co), UsageDetails
    emptyUDs)
    specExpr SpecEnv
    _   (Lit Literal
    lit)     = (OutExpr, UsageDetails) -> SpecM (OutExpr, UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (Literal -> OutExpr
    forall b. Literal -> Expr b
    Lit Literal
    lit,                   UsageDetails
    emptyUDs)
    specExpr SpecEnv
    env (Cast OutExpr
    e Coercion
    co)
      = do { (e', uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    e
           ; return ((mkCast e' (substCo env co)), uds) }
    specExpr SpecEnv
    env (Tick CoreTickish
    tickish OutExpr
    body)
      = do { (body', uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    body
           ; return (Tick (specTickish env tickish) body', uds) }

    ---------------- Applications might generate a call instance --------------------
    specExpr SpecEnv
    env expr :: OutExpr
    expr@(App {})
      = do { let (OutExpr
    fun_in, [OutExpr]
    args_in) = OutExpr -> (OutExpr, [OutExpr])
    forall b. Expr b -> (Expr b, [Expr b])
    collectArgs OutExpr
    expr
           ; (args_out, uds_args) <- (OutExpr -> SpecM (OutExpr, UsageDetails))
    -> [OutExpr] -> SpecM ([OutExpr], UsageDetails)
    forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM (SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env) [OutExpr]
    args_in
           ; let env_args = SpecEnv
    env SpecEnv -> FloatedDictBinds -> SpecEnv
    `bringFloatedDictsIntoScope` UsageDetails -> FloatedDictBinds
    ud_binds UsageDetails
    uds_args
                    -- Some dicts may have floated out of args_in;
                    -- they should be in scope for fireRewriteRules (#21689)
                 (fun_in', args_out') = fireRewriteRules env_args fun_in args_out
           ; (fun_out', uds_fun) <- specExpr env fun_in'
           ; let uds_call = SpecEnv -> OutExpr -> [OutExpr] -> UsageDetails
    mkCallUDs SpecEnv
    env OutExpr
    fun_out' [OutExpr]
    args_out'
           ; return (fun_out' `mkApps` args_out', uds_fun `thenUDs` uds_call `thenUDs` uds_args) }

    ---------------- Lambda/case require dumping of usage details --------------------
    specExpr SpecEnv
    env e :: OutExpr
    e@(Lam {})
      = SpecEnv -> [Id] -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specLam SpecEnv
    env' [Id]
    bndrs' OutExpr
    body
      where
        ([Id]
    bndrs, OutExpr
    body)  = OutExpr -> ([Id], OutExpr)
    forall b. Expr b -> ([b], Expr b)
    collectBinders OutExpr
    e
        (SpecEnv
    env', [Id]
    bndrs') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bndrs
            -- More efficient to collect a group of binders together all at once
            -- and we don't want to split a lambda group with dumped bindings

    specExpr SpecEnv
    env (Case OutExpr
    scrut Id
    case_bndr Kind
    ty [Alt Id]
    alts)
      = do { (scrut', scrut_uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    scrut
           ; (scrut'', case_bndr', alts', alts_uds)
                 <- specCase env scrut' case_bndr alts
    --       ; pprTrace "specExpr:case" (vcat
    --            [ text "scrut" <+> ppr scrut, text "scrut'" <+> ppr scrut'
    --            , text "case_bndr'" <+> ppr case_bndr'
    --            , text "alts_uds" <+> ppr alts_uds
    --            ])
           ; return (Case scrut'' case_bndr' (substTy env ty) alts'
                    , scrut_uds `thenUDs` alts_uds) }

    ---------------- Finally, let is the interesting case --------------------
    specExpr SpecEnv
    env (Let InBind
    bind OutExpr
    body)
      = do { (binds', body', uds) <- TopLevelFlag
    -> SpecEnv
    -> InBind
    -> (SpecEnv -> SpecM (OutExpr, UsageDetails))
    -> SpecM (CoreProgram, OutExpr, UsageDetails)
    forall body.
    TopLevelFlag
    -> SpecEnv
    -> InBind
    -> (SpecEnv -> SpecM (body, UsageDetails))
    -> SpecM (CoreProgram, body, UsageDetails)
    specBind TopLevelFlag
    NotTopLevel SpecEnv
    env InBind
    bind ((SpecEnv -> SpecM (OutExpr, UsageDetails))
     -> SpecM (CoreProgram, OutExpr, UsageDetails))
    -> (SpecEnv -> SpecM (OutExpr, UsageDetails))
    -> SpecM (CoreProgram, OutExpr, UsageDetails)
    forall a b. (a -> b) -> a -> b
    $ \SpecEnv
    body_env ->
                                     -- pprTrace "specExpr:let" (ppr (se_subst body_env) $$ ppr body) $
                                     SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    body_env OutExpr
    body
             -- All done
           ; return (foldr Let body' binds', uds) }

    -- See Note [Specialisation modulo dictionary selectors]
    --     Note [ClassOp/DFun selection]
    --     Note [Fire rules in the specialiser]
    fireRewriteRules :: SpecEnv -> InExpr -> [OutExpr] -> (InExpr, [OutExpr])
    fireRewriteRules :: SpecEnv -> OutExpr -> [OutExpr] -> (OutExpr, [OutExpr])
    fireRewriteRules SpecEnv
    env (Var Id
    f) [OutExpr]
    args
      | Just (CoreRule
    rule, OutExpr
    expr) <- SpecEnv
    -> Id
    -> [OutExpr]
    -> CompilerPhase
    -> [CoreRule]
    -> Maybe (CoreRule, OutExpr)
    specLookupRule SpecEnv
    env Id
    f [OutExpr]
    args CompilerPhase
    InitialPhase (RuleEnv -> Id -> [CoreRule]
    getRules (SpecEnv -> RuleEnv
    se_rules SpecEnv
    env) Id
    f)
      , let rest_args :: [OutExpr]
    rest_args    = Int -> [OutExpr] -> [OutExpr]
    forall a. Int -> [a] -> [a]
    drop (CoreRule -> Int
    ruleArity CoreRule
    rule) [OutExpr]
    args -- See Note [Extra args in the target]
            zapped_subst :: Subst
    zapped_subst = Subst -> Subst
    Core.zapSubst (SpecEnv -> Subst
    se_subst SpecEnv
    env)
            expr' :: OutExpr
    expr'        = HasDebugCallStack => SimpleOpts -> Subst -> OutExpr -> OutExpr
    SimpleOpts -> Subst -> OutExpr -> OutExpr
    simpleOptExprWith SimpleOpts
    defaultSimpleOpts Subst
    zapped_subst OutExpr
    expr
                           -- simplOptExpr needed because lookupRule returns
                           --   (\x y. rhs) arg1 arg2
      , (OutExpr
    fun, [OutExpr]
    args) <- OutExpr -> (OutExpr, [OutExpr])
    forall b. Expr b -> (Expr b, [Expr b])
    collectArgs OutExpr
    expr'
      = SpecEnv -> OutExpr -> [OutExpr] -> (OutExpr, [OutExpr])
    fireRewriteRules SpecEnv
    env OutExpr
    fun ([OutExpr]
    args[OutExpr] -> [OutExpr] -> [OutExpr]
    forall a. [a] -> [a] -> [a]
    ++[OutExpr]
    rest_args)
    fireRewriteRules SpecEnv
    _ OutExpr
    fun [OutExpr]
    args = (OutExpr
    fun, [OutExpr]
    args)

    --------------
    specLam :: SpecEnv -> [OutBndr] -> InExpr -> SpecM (OutExpr, UsageDetails)
    -- The binders have been substituted, but the body has not
    specLam :: SpecEnv -> [Id] -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specLam SpecEnv
    env [Id]
    bndrs OutExpr
    body
      | [Id] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    bndrs
      = SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    body
      | Bool
    otherwise
      = do { (body', uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    body
           ; let (free_uds, dumped_dbs) = dumpUDs bndrs uds
           ; return (mkLams bndrs (wrapDictBindsE dumped_dbs body'), free_uds) }

    --------------
    specTickish :: SpecEnv -> CoreTickish -> CoreTickish
    specTickish :: SpecEnv -> CoreTickish -> CoreTickish
    specTickish (SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst }) CoreTickish
    bp = Subst -> CoreTickish -> CoreTickish
    substTickish Subst
    subst CoreTickish
    bp

    --------------
    specCase :: SpecEnv
             -> OutExpr             -- Scrutinee, already done
             -> InId -> [InAlt]
             -> SpecM ( OutExpr     -- New scrutinee
                      , OutId
                      , [OutAlt]
                      , UsageDetails)
    specCase :: SpecEnv
    -> OutExpr
    -> Id
    -> [Alt Id]
    -> SpecM (OutExpr, Id, [Alt Id], UsageDetails)
    specCase SpecEnv
    env OutExpr
    scrut' Id
    case_bndr [Alt AltCon
    con [Id]
    args OutExpr
    rhs]
      | -- See Note [Floating dictionaries out of cases]
        OutExpr -> Kind -> Bool
    interestingDict OutExpr
    scrut' (Id -> Kind
    idType Id
    case_bndr)
      , Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    case_bndr Bool -> Bool -> Bool
    && [Id] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    sc_args')
      = do { case_bndr_flt :| sc_args_flt <- (Id -> UniqSM Id) -> NonEmpty Id -> UniqSM (NonEmpty Id)
    forall (t :: * -> *) (m :: * -> *) a b.
    (Traversable t, Monad m) =>
    (a -> m b) -> t a -> m (t b)
    forall (m :: * -> *) a b.
    Monad m =>
    (a -> m b) -> NonEmpty a -> m (NonEmpty b)
    mapM Id -> UniqSM Id
    forall {m :: * -> *}. MonadUnique m => Id -> m Id
    clone_me (Id
    case_bndr' Id -> [Id] -> NonEmpty Id
    forall a. a -> [a] -> NonEmpty a
    :| [Id]
    sc_args')

           ; let case_bndr_flt' = Id
    case_bndr_flt Id -> OutExpr -> Id
    `addDictUnfolding` OutExpr
    scrut'
                 scrut_bind     = InBind -> DictBind
    mkDB (Id -> OutExpr -> InBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    case_bndr_flt OutExpr
    scrut')

                 sc_args_flt' = (Id -> OutExpr -> Id) -> [Id] -> [OutExpr] -> [Id]
    forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
    zipWith Id -> OutExpr -> Id
    addDictUnfolding [Id]
    sc_args_flt [OutExpr]
    sc_rhss
                 sc_rhss      = [ OutExpr -> Id -> Kind -> [Alt Id] -> OutExpr
    forall b. Expr b -> b -> Kind -> [Alt b] -> Expr b
    Case (Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    case_bndr_flt') Id
    case_bndr' (Id -> Kind
    idType Id
    sc_arg')
                                       [AltCon -> [Id] -> OutExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args' (Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    sc_arg')]
                                | Id
    sc_arg' <- [Id]
    sc_args' ]
                 cb_set       = Id -> VarSet
    unitVarSet Id
    case_bndr_flt'
                 sc_binds     = [ DB { db_bind :: InBind
    db_bind = Id -> OutExpr -> InBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    sc_arg_flt OutExpr
    sc_rhs, db_fvs :: VarSet
    db_fvs  = VarSet
    cb_set }
                                | (Id
    sc_arg_flt, OutExpr
    sc_rhs) <- [Id]
    sc_args_flt' [Id] -> [OutExpr] -> [(Id, OutExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [OutExpr]
    sc_rhss ]

                 flt_binds    = DictBind
    scrut_bind DictBind -> [DictBind] -> [DictBind]
    forall a. a -> [a] -> [a]
    : [DictBind]
    sc_binds

                 -- Extend the substitution for RHS to map the *original* binders
                 -- to their floated versions.
                 mb_sc_flts :: [Maybe DictId]
                 mb_sc_flts = (Id -> Maybe Id) -> [Id] -> [Maybe Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (VarEnv Id -> Id -> Maybe Id
    forall a. VarEnv a -> Id -> Maybe a
    lookupVarEnv VarEnv Id
    clone_env) [Id]
    args'
                 clone_env  = [Id] -> [Id] -> VarEnv Id
    forall a. [Id] -> [a] -> VarEnv a
    zipVarEnv [Id]
    sc_args' [Id]
    sc_args_flt'

                 subst_prs  = (Id
    case_bndr, Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    case_bndr_flt)
                            (Id, OutExpr) -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a. a -> [a] -> [a]
    : [ (Id
    arg, Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    sc_flt)
                              | (Id
    arg, Just Id
    sc_flt) <- [Id]
    args [Id] -> [Maybe Id] -> [(Id, Maybe Id)]
    forall a b. [a] -> [b] -> [(a, b)]
    `zip` [Maybe Id]
    mb_sc_flts ]
                 subst'   = SpecEnv -> Subst
    se_subst SpecEnv
    env_rhs
                            Subst -> [Id] -> Subst
    `Core.extendSubstInScopeList` (Id
    case_bndr_flt' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    sc_args_flt')
                            Subst -> [(Id, OutExpr)] -> Subst
    `Core.extendIdSubstList`      [(Id, OutExpr)]
    subst_prs
                 env_rhs' = SpecEnv
    env_rhs { se_subst = subst' }

           ; (rhs', rhs_uds)   <- specExpr env_rhs' rhs
           ; let (free_uds, dumped_dbs) = dumpUDs (case_bndr':args') rhs_uds
                 all_uds = [DictBind]
    flt_binds [DictBind] -> UsageDetails -> UsageDetails
    `consDictBinds` UsageDetails
    free_uds
                 alt'    = AltCon -> [Id] -> OutExpr -> Alt Id
    forall b. AltCon -> [b] -> Expr b -> Alt b
    Alt AltCon
    con [Id]
    args' (OrdList DictBind -> OutExpr -> OutExpr
    wrapDictBindsE OrdList DictBind
    dumped_dbs OutExpr
    rhs')
    --       ; pprTrace "specCase" (ppr case_bndr $$ ppr scrut_bind) $
           ; return (Var case_bndr_flt, case_bndr', [alt'], all_uds) }
      where
        (SpecEnv
    env_rhs, (Id
    case_bndr':[Id]
    args')) = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env (Id
    case_bndrId -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    :[Id]
    args)
        sc_args' :: [Id]
    sc_args' = (Id -> Bool) -> [Id] -> [Id]
    forall a. (a -> Bool) -> [a] -> [a]
    filter Id -> Bool
    is_flt_sc_arg [Id]
    args'

        clone_me :: Id -> m Id
    clone_me Id
    bndr = do { uniq <- m Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
                           ; return (mkUserLocalOrCoVar occ uniq wght ty loc) }
           where
             name :: Name
    name = Id -> Name
    idName Id
    bndr
             wght :: Kind
    wght = Id -> Kind
    idMult Id
    bndr
             ty :: Kind
    ty   = Id -> Kind
    idType Id
    bndr
             occ :: OccName
    occ  = Name -> OccName
    nameOccName Name
    name
             loc :: SrcSpan
    loc  = Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    name

        arg_set :: VarSet
    arg_set = [Id] -> VarSet
    mkVarSet [Id]
    args'
        is_flt_sc_arg :: Id -> Bool
    is_flt_sc_arg Id
    var =  Id -> Bool
    isId Id
    var
                          Bool -> Bool -> Bool
    && Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    var)
                          Bool -> Bool -> Bool
    && Kind -> Bool
    isDictTy Kind
    var_ty
                          Bool -> Bool -> Bool
    && Kind -> VarSet
    tyCoVarsOfType Kind
    var_ty VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    arg_set
           where
             var_ty :: Kind
    var_ty = Id -> Kind
    idType Id
    var

    specCase SpecEnv
    env OutExpr
    scrut Id
    case_bndr [Alt Id]
    alts
      = do { (alts', uds_alts) <- (Alt Id -> SpecM (Alt Id, UsageDetails))
    -> [Alt Id] -> SpecM ([Alt Id], UsageDetails)
    forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM Alt Id -> SpecM (Alt Id, UsageDetails)
    spec_alt [Alt Id]
    alts
           ; return (scrut, case_bndr', alts', uds_alts) }
      where
        (SpecEnv
    env_alt, Id
    case_bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    case_bndr
        spec_alt :: Alt Id -> SpecM (Alt Id, UsageDetails)
    spec_alt (Alt AltCon
    con [Id]
    args OutExpr
    rhs)
          = do { (rhs', uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env_rhs OutExpr
    rhs
               ; let (free_uds, dumped_dbs) = dumpUDs (case_bndr' : args') uds
    --           ; unless (isNilOL dumped_dbs) $
    --             pprTrace "specAlt" (vcat
    --                 [text "case_bndr', args" <+> (ppr case_bndr' $$ ppr args)
    --                 ,text "dumped" <+> ppr dumped_dbs ]) return ()
               ; return (Alt con args' (wrapDictBindsE dumped_dbs rhs'), free_uds) }
            where
              (SpecEnv
    env_rhs, [Id]
    args') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env_alt [Id]
    args

    {- Note [Fire rules in the specialiser]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this (#21851)

        module A where
          f :: Num b => b -> (b, b)
          f x = (x + 1, snd (f x))
          {-# SPECIALIZE f :: Int -> (Int, Int) #-}

        module B (g') where
          import A

          g :: Num a => a -> a
          g x = fst (f x)
          {-# NOINLINE[99] g #-}

          h :: Int -> Int
          h = g

    Note that `f` has the CPR property, and so will worker/wrapper.

    The call to `g` in `h` will make us specialise `g @Int`. And the specialised
    version of `g` will contain the call `f @Int`; but in the subsequent run of
    the Simplifier, there will be a competition between:
    * The user-supplied SPECIALISE rule for `f`
    * The inlining of the wrapper for `f`
    In fact, the latter wins -- see Note [Rewrite rules and inlining] in
    GHC.Core.Opt.Simplify.Iteration.  However, it a bit fragile.

    Moreover consider (test T21851_2):

        module A
          f :: (Ord a, Show b) => a -> b -> blah
          {-# RULE forall b. f @Int @b = wombat #-}

          wombat :: Show b => Int -> b -> blah
          wombat = blah

        module B
          import A
          g :: forall a. Ord a => blah
          g @a = ...g...f @a @Char....

          h = ....g @Int....

    Now, in module B, GHC will specialise `g @Int`, which will lead to a
    call `f @Int @Char`.  If we immediately (in the specialiser) rewrite
    that to `womabat @Char`, we have a chance to specialise `wombat`.

    Conclusion: it's treat if the Specialiser fires RULEs itself.
    It's not hard to achieve: see `fireRewriteRules`. The only tricky bit is
    making sure that we have a reasonably up to date EPS rule base. Currently
    we load it up just once, in `initRuleEnv`, called at the beginning of
    `specProgram`.

    NB: you might wonder if running rules in the specialiser (this Note)
    renders Note [Rewrite rules and inlining] in the Simplifier redundant.
    That is, if we run rules in the specialiser, does it matter if we make
    rules "win" over inlining in the Simplifier?  Yes, it does!  See the
    discussion in #21851.

    Note [Floating dictionaries out of cases]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       g = \d. case d of { MkD sc ... -> ...(f sc)... }
    Naively we can't float d2's binding out of the case expression,
    because 'sc' is bound by the case, and that in turn means we can't
    specialise f, which seems a pity.

    So we invert the case, by floating out a binding
    for 'sc_flt' thus:
        sc_flt = case d of { MkD sc ... -> sc }
    Now we can float the call instance for 'f'.  Indeed this is just
    what'll happen if 'sc' was originally bound with a let binding,
    but case is more efficient, and necessary with equalities. So it's
    good to work with both.

    You might think that this won't make any difference, because the
    call instance will only get nuked by the \d.  BUT if 'g' itself is
    specialised, then transitively we should be able to specialise f.

    In general, given
       case e of cb { MkD sc ... -> ...(f sc)... }
    we transform to
       let cb_flt = e
           sc_flt = case cb_flt of { MkD sc ... -> sc }
       in
       case cb_flt of bg { MkD sc ... -> ....(f sc_flt)... }

    The "_flt" things are the floated binds; we use the current substitution
    to substitute sc -> sc_flt in the RHS

    ************************************************************************
    *                                                                      *
                         Dealing with a binding
    *                                                                      *
    ************************************************************************
    -}

    bringFloatedDictsIntoScope :: SpecEnv -> FloatedDictBinds -> SpecEnv
    bringFloatedDictsIntoScope :: SpecEnv -> FloatedDictBinds -> SpecEnv
    bringFloatedDictsIntoScope SpecEnv
    env (FDB { fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    dx_bndrs })
      = -- pprTrace "brought into scope" (ppr dx_bndrs) $
        SpecEnv
    env {se_subst=subst'}
      where
       subst' :: Subst
    subst' = SpecEnv -> Subst
    se_subst SpecEnv
    env Subst -> VarSet -> Subst
    `Core.extendSubstInScopeSet` VarSet
    dx_bndrs

    specBind :: TopLevelFlag
             -> SpecEnv    -- At top-level only, this env already has the
                           -- top level binders in scope
             -> InBind
             -> (SpecEnv -> SpecM (body, UsageDetails))    -- Process the body
             -> SpecM ( [OutBind]           -- New bindings
                      , body                -- Body
                      , UsageDetails)       -- And info to pass upstream

    -- Returned UsageDetails:
    --    No calls for binders of this bind
    specBind :: forall body.
    TopLevelFlag
    -> SpecEnv
    -> InBind
    -> (SpecEnv -> SpecM (body, UsageDetails))
    -> SpecM (CoreProgram, body, UsageDetails)
    specBind TopLevelFlag
    top_lvl SpecEnv
    env (NonRec Id
    fn OutExpr
    rhs) SpecEnv -> SpecM (body, UsageDetails)
    do_body
      = do { (rhs', rhs_uds) <- SpecEnv -> OutExpr -> SpecM (OutExpr, UsageDetails)
    specExpr SpecEnv
    env OutExpr
    rhs

           ; (body_env1, fn1) <- case top_lvl of
                                   TopLevelFlag
    TopLevel    -> (SpecEnv, Id) -> UniqSM (SpecEnv, Id)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, Id
    fn)
                                   TopLevelFlag
    NotTopLevel -> SpecEnv -> Id -> UniqSM (SpecEnv, Id)
    cloneBndrSM SpecEnv
    env Id
    fn

           ; let fn2 | Unfolding -> Bool
    isStableUnfolding (Id -> Unfolding
    idUnfolding Id
    fn1) = Id
    fn1
                     | Bool
    otherwise = Id
    fn1 Id -> Unfolding -> Id
    `setIdUnfolding` UnfoldingOpts -> OutExpr -> Unfolding
    mkSimpleUnfolding UnfoldingOpts
    defaultUnfoldingOpts OutExpr
    rhs'
                 -- Update the unfolding with the perhaps-simpler or more specialised rhs'
                 -- This is important: see Note [Update unfolding after specialisation]
                 -- And in any case cloneBndrSM discards non-Stable unfoldings

                 fn3 = Id -> Id
    floatifyIdDemandInfo Id
    fn2
                 -- We zap the demand info because the binding may float,
                 -- which would invalidate the demand info (see #17810 for example).
                 -- Destroying demand info is not terrible; specialisation is
                 -- always followed soon by demand analysis.
                 -- See Note [Floatifying demand info when floating] in GHC.Core.Opt.SetLevels

                 body_env2 = SpecEnv
    body_env1 SpecEnv -> FloatedDictBinds -> SpecEnv
    `bringFloatedDictsIntoScope` UsageDetails -> FloatedDictBinds
    ud_binds UsageDetails
    rhs_uds
                                       SpecEnv -> Id -> SpecEnv
    `extendInScope` Id
    fn3
                                       -- bringFloatedDictsIntoScope: see #23567

           ; (body', body_uds) <- do_body body_env2

           ; (fn4, spec_defns, body_uds1) <- specDefn env body_uds fn3 rhs

           ; let (free_uds, dump_dbs, float_all) = dumpBindUDs [fn4] body_uds1
                 all_free_uds                    = UsageDetails
    free_uds UsageDetails -> UsageDetails -> UsageDetails
    `thenUDs` UsageDetails
    rhs_uds

                 pairs = [(Id, OutExpr)]
    spec_defns [(Id, OutExpr)] -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id
    fn4, OutExpr
    rhs')]
                            -- fn4 mentions the spec_defns in its rules,
                            -- so put the latter first

                 final_binds :: [DictBind]
                 -- See Note [From non-recursive to recursive]
                 final_binds | Bool -> Bool
    not (OrdList DictBind -> Bool
    forall a. OrdList a -> Bool
    isNilOL OrdList DictBind
    dump_dbs)
                             , Bool -> Bool
    not ([(Id, OutExpr)] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [(Id, OutExpr)]
    spec_defns)
                             = [[(Id, OutExpr)] -> OrdList DictBind -> DictBind
    recWithDumpedDicts [(Id, OutExpr)]
    pairs OrdList DictBind
    dump_dbs]
                             | Bool
    otherwise
                             = [InBind -> DictBind
    mkDB (InBind -> DictBind) -> InBind -> DictBind
    forall a b. (a -> b) -> a -> b
    $ Id -> OutExpr -> InBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    b OutExpr
    r | (Id
    b,OutExpr
    r) <- [(Id, OutExpr)]
    pairs]
                               [DictBind] -> [DictBind] -> [DictBind]
    forall a. [a] -> [a] -> [a]
    ++ OrdList DictBind -> [DictBind]
    forall a. OrdList a -> [a]
    fromOL OrdList DictBind
    dump_dbs

                 can_float_this_one = OutExpr -> Kind -> Bool
    exprIsTopLevelBindable OutExpr
    rhs (Id -> Kind
    idType Id
    fn)
                 -- exprIsTopLevelBindable: see Note [Care with unlifted bindings]

           ; if float_all && can_float_this_one then
                 -- Rather than discard the calls mentioning the bound variables
                 -- we float this (dictionary) binding along with the others
                  return ([], body', all_free_uds `snocDictBinds` final_binds)
             else
                 -- No call in final_uds mentions bound variables,
                 -- so we can just leave the binding here
                  return (map db_bind final_binds, body', all_free_uds) }

    specBind TopLevelFlag
    top_lvl SpecEnv
    env (Rec [(Id, OutExpr)]
    pairs) SpecEnv -> SpecM (body, UsageDetails)
    do_body
           -- Note [Specialising a recursive group]
      = do { let ([Id]
    bndrs,[OutExpr]
    rhss) = [(Id, OutExpr)] -> ([Id], [OutExpr])
    forall a b. [(a, b)] -> ([a], [b])
    unzip [(Id, OutExpr)]
    pairs

           ; (rec_env, bndrs1) <- case TopLevelFlag
    top_lvl of
                                     TopLevelFlag
    TopLevel    -> (SpecEnv, [Id]) -> UniqSM (SpecEnv, [Id])
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return (SpecEnv
    env, [Id]
    bndrs)
                                     TopLevelFlag
    NotTopLevel -> SpecEnv -> [Id] -> UniqSM (SpecEnv, [Id])
    cloneRecBndrsSM SpecEnv
    env [Id]
    bndrs

           ; (rhss', rhs_uds)  <- mapAndCombineSM (specExpr rec_env) rhss
           ; (body', body_uds) <- do_body rec_env

           ; let scope_uds = UsageDetails
    body_uds UsageDetails -> UsageDetails -> UsageDetails
    `thenUDs` UsageDetails
    rhs_uds
                           -- Includes binds and calls arising from rhss

           ; (bndrs2, spec_defns2, uds2) <- specDefns rec_env scope_uds (bndrs1 `zip` rhss)
             -- bndrs2 is like bndrs1, but with RULES added

           ; (bndrs3, spec_defns3, uds3)
                 <- if null spec_defns2  -- Common case: no specialisation
                    then return (bndrs2, [], uds2)
                    else do {            -- Specialisation occurred; do it again
                              (bndrs3, spec_defns3, uds3)
                                  <- specDefns rec_env uds2 (bndrs2 `zip` rhss)
                            ; return (bndrs3, spec_defns3 ++ spec_defns2, uds3) }

           ; let (final_uds, dumped_dbs, float_all) = dumpBindUDs bndrs1 uds3
                 final_bind = [(Id, OutExpr)] -> OrdList DictBind -> DictBind
    recWithDumpedDicts ([(Id, OutExpr)]
    spec_defns3 [(Id, OutExpr)] -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [Id] -> [OutExpr] -> [(Id, OutExpr)]
    forall a b. [a] -> [b] -> [(a, b)]
    zip [Id]
    bndrs3 [OutExpr]
    rhss')
                                                 OrdList DictBind
    dumped_dbs

           ; if float_all then
                  return ([], body', final_uds `snocDictBind` final_bind)
             else
                  return ([db_bind final_bind], body', final_uds) }

    ---------------------------
    specDefns :: SpecEnv
              -> UsageDetails               -- Info on how it is used in its scope
              -> [(OutId,InExpr)]           -- The things being bound and their un-processed RHS
              -> SpecM ([OutId],            -- Original Ids with RULES added
                        [(OutId,OutExpr)],  -- Extra, specialised bindings
                        UsageDetails)       -- Stuff to fling upwards from the specialised versions

    -- Specialise a list of bindings (the contents of a Rec), but flowing usages
    -- upwards binding by binding.  Example: { f = ...g ...; g = ...f .... }
    -- Then if the input CallDetails has a specialised call for 'g', whose specialisation
    -- in turn generates a specialised call for 'f', we catch that in this one sweep.
    -- But not vice versa (it's a fixpoint problem).

    specDefns :: SpecEnv
    -> UsageDetails
    -> [(Id, OutExpr)]
    -> SpecM ([Id], [(Id, OutExpr)], UsageDetails)
    specDefns SpecEnv
    _env UsageDetails
    uds []
      = ([Id], [(Id, OutExpr)], UsageDetails)
    -> SpecM ([Id], [(Id, OutExpr)], UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [], UsageDetails
    uds)
    specDefns SpecEnv
    env UsageDetails
    uds ((Id
    bndr,OutExpr
    rhs):[(Id, OutExpr)]
    pairs)
      = do { (bndrs1, spec_defns1, uds1) <- SpecEnv
    -> UsageDetails
    -> [(Id, OutExpr)]
    -> SpecM ([Id], [(Id, OutExpr)], UsageDetails)
    specDefns SpecEnv
    env UsageDetails
    uds  [(Id, OutExpr)]
    pairs
           ; (bndr1, spec_defns2, uds2)  <- specDefn  env uds1 bndr rhs
           ; return (bndr1 : bndrs1, spec_defns1 ++ spec_defns2, uds2) }

    ---------------------------
    specDefn :: SpecEnv
             -> UsageDetails                -- Info on how it is used in its scope
             -> OutId -> InExpr             -- The thing being bound and its un-processed RHS
             -> SpecM (Id,                  -- Original Id with added RULES
                       [(Id,CoreExpr)],     -- Extra, specialised bindings
                       UsageDetails)        -- Stuff to fling upwards from the specialised versions

    specDefn :: SpecEnv
    -> UsageDetails
    -> Id
    -> OutExpr
    -> SpecM (Id, [(Id, OutExpr)], UsageDetails)
    specDefn SpecEnv
    env UsageDetails
    body_uds Id
    fn OutExpr
    rhs
      = do { let (UsageDetails
    body_uds_without_me, [CallInfo]
    calls_for_me) = Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe Id
    fn UsageDetails
    body_uds
                 rules_for_me :: [CoreRule]
    rules_for_me = Id -> [CoreRule]
    idCoreRules Id
    fn
                 -- Bring into scope the binders from the floated dicts
                 env_w_dict_bndrs :: SpecEnv
    env_w_dict_bndrs = SpecEnv -> FloatedDictBinds -> SpecEnv
    bringFloatedDictsIntoScope SpecEnv
    env (UsageDetails -> FloatedDictBinds
    ud_binds UsageDetails
    body_uds)

           ; (rules, spec_defns, spec_uds) <- Bool
    -> SpecEnv
    -> [CoreRule]
    -> [CallInfo]
    -> Id
    -> OutExpr
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    specCalls Bool
    False SpecEnv
    env_w_dict_bndrs
                                                        [CoreRule]
    rules_for_me [CallInfo]
    calls_for_me Id
    fn OutExpr
    rhs

           ; return ( fn `addIdSpecialisations` rules
                    , spec_defns
                    , body_uds_without_me `thenUDs` spec_uds) }
                    -- It's important that the `thenUDs` is this way
                    -- round, because body_uds_without_me may bind
                    -- dictionaries that are used in calls_for_me passed
                    -- to specDefn.  So the dictionary bindings in
                    -- spec_uds may mention dictionaries bound in
                    -- body_uds_without_me

    ---------------------------
    specCalls :: Bool              -- True  =>  specialising imported fn
                                   -- False =>  specialising local fn
              -> SpecEnv
              -> [CoreRule]        -- Existing RULES for the fn
              -> [CallInfo]
              -> OutId -> InExpr
              -> SpecM SpecInfo    -- New rules, specialised bindings, and usage details

    -- This function checks existing rules, and does not create
    -- duplicate ones. So the caller does not need to do this filtering.
    -- See 'already_covered'

    type SpecInfo = ( [CoreRule]       -- Specialisation rules
                    , [(Id,CoreExpr)]  -- Specialised definition
                    , UsageDetails )   -- Usage details from specialised RHSs

    specCalls :: Bool
    -> SpecEnv
    -> [CoreRule]
    -> [CallInfo]
    -> Id
    -> OutExpr
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    specCalls Bool
    spec_imp SpecEnv
    env [CoreRule]
    existing_rules [CallInfo]
    calls_for_me Id
    fn OutExpr
    rhs
            -- The first case is the interesting one
      |  [CallInfo] -> Bool
    forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [CallInfo]
    calls_for_me               -- And there are some calls to specialise
      Bool -> Bool -> Bool
    && Bool -> Bool
    not (Activation -> Bool
    isNeverActive (Id -> Activation
    idInlineActivation Id
    fn))
            -- Don't specialise NOINLINE things
            -- See Note [Auto-specialisation and RULES]
            --
            -- Don't specialise OPAQUE things, see Note [OPAQUE pragma].
            -- Since OPAQUE things are always never-active (see
            -- GHC.Parser.PostProcess.mkOpaquePragma) this guard never fires for
            -- OPAQUE things.

    --   && not (certainlyWillInline (idUnfolding fn))      -- And it's not small
    --      See Note [Inline specialisations] for why we do not
    --      switch off specialisation for inline functions

      = -- pprTrace "specCalls: some" (vcat
        --   [ text "function" <+> ppr fn
        --   , text "calls:" <+> ppr calls_for_me
        --   , text "subst" <+> ppr (se_subst env) ]) $
        (([CoreRule], [(Id, OutExpr)], UsageDetails)
     -> CallInfo -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails))
    -> ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> [CallInfo]
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    forall (t :: * -> *) (m :: * -> *) b a.
    (Foldable t, Monad m) =>
    (b -> a -> m b) -> b -> t a -> m b
    foldlM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> CallInfo -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    spec_call ([], [], UsageDetails
    emptyUDs) [CallInfo]
    calls_for_me

      | Bool
    otherwise   -- No calls or RHS doesn't fit our preconceptions
      = Bool
    -> String
    -> SDoc
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    forall a. HasCallStack => Bool -> String -> SDoc -> a -> a
    warnPprTrace (Bool -> Bool
    not (OutExpr -> Bool
    exprIsTrivial OutExpr
    rhs) Bool -> Bool -> Bool
    && [CallInfo] -> Bool
    forall (f :: * -> *) a. Foldable f => f a -> Bool
    notNull [CallInfo]
    calls_for_me Bool -> Bool -> Bool
    && Bool -> Bool
    not (Id -> Bool
    isClassOpId Id
    fn))
              String
    "Missed specialisation opportunity for" (Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ SDoc
    trace_doc) (SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
     -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails))
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    forall a b. (a -> b) -> a -> b
    $
              -- isClassOpId: class-op Ids never inline; we specialise them
              -- through fireRewriteRules. So don't complain about missed opportunities
              -- Note [Specialisation shape]
        -- pprTrace "specCalls: none" (ppr fn <+> ppr calls_for_me) $
        ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], [], UsageDetails
    emptyUDs)
      where
        trace_doc :: SDoc
    trace_doc = [SDoc] -> SDoc
    forall doc. IsLine doc => [doc] -> doc
    sep [ [Id] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Id]
    rhs_bndrs, Activation -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr (Id -> Activation
    idInlineActivation Id
    fn) ]

        fn_type :: Kind
    fn_type   = Id -> Kind
    idType Id
    fn
        fn_arity :: Int
    fn_arity  = Id -> Int
    idArity Id
    fn
        fn_unf :: Unfolding
    fn_unf    = Id -> Unfolding
    realIdUnfolding Id
    fn  -- Ignore loop-breaker-ness here
        inl_prag :: InlinePragma
    inl_prag  = Id -> InlinePragma
    idInlinePragma Id
    fn
        inl_act :: Activation
    inl_act   = InlinePragma -> Activation
    inlinePragmaActivation InlinePragma
    inl_prag
        is_local :: Bool
    is_local  = Id -> Bool
    isLocalId Id
    fn
        is_dfun :: Bool
    is_dfun   = Id -> Bool
    isDFunId Id
    fn
        dflags :: DynFlags
    dflags    = SpecEnv -> DynFlags
    se_dflags SpecEnv
    env
        this_mod :: Module
    this_mod  = SpecEnv -> Module
    se_module SpecEnv
    env
            -- Figure out whether the function has an INLINE pragma
            -- See Note [Inline specialisations]

        ([Id]
    rhs_bndrs, OutExpr
    rhs_body) = OutExpr -> ([Id], OutExpr)
    collectBindersPushingCo OutExpr
    rhs
                                -- See Note [Account for casts in binding]

        already_covered :: SpecEnv -> [CoreRule] -> [CoreExpr] -> Bool
        already_covered :: SpecEnv -> [CoreRule] -> [OutExpr] -> Bool
    already_covered SpecEnv
    env [CoreRule]
    new_rules [OutExpr]
    args      -- Note [Specialisations already covered]
           = Maybe (CoreRule, OutExpr) -> Bool
    forall a. Maybe a -> Bool
    isJust (SpecEnv
    -> Id
    -> [OutExpr]
    -> CompilerPhase
    -> [CoreRule]
    -> Maybe (CoreRule, OutExpr)
    specLookupRule SpecEnv
    env Id
    fn [OutExpr]
    args (Activation -> CompilerPhase
    beginPhase Activation
    inl_act)
                                    ([CoreRule]
    new_rules [CoreRule] -> [CoreRule] -> [CoreRule]
    forall a. [a] -> [a] -> [a]
    ++ [CoreRule]
    existing_rules))
             -- Rules: we look both in the new_rules (generated by this invocation
             --   of specCalls), and in existing_rules (passed in to specCalls)
             -- inl_act: is the activation we are going to put in the new SPEC
             --   rule; so we want to see if it is covered by another rule with
             --   that same activation.

        ----------------------------------------------------------
            -- Specialise to one particular call pattern
        spec_call :: SpecInfo                         -- Accumulating parameter
                  -> CallInfo                         -- Call instance
                  -> SpecM SpecInfo
        spec_call :: ([CoreRule], [(Id, OutExpr)], UsageDetails)
    -> CallInfo -> SpecM ([CoreRule], [(Id, OutExpr)], UsageDetails)
    spec_call spec_acc :: ([CoreRule], [(Id, OutExpr)], UsageDetails)
    spec_acc@([CoreRule]
    rules_acc, [(Id, OutExpr)]
    pairs_acc, UsageDetails
    uds_acc) _ci :: CallInfo
    _ci@(CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    call_args })
          = -- See Note [Specialising Calls]
            do { let all_call_args :: [SpecArg]
    all_call_args | Bool
    is_dfun   = [SpecArg]
    saturating_call_args -- See Note [Specialising DFuns]
                                   | Bool
    otherwise = [SpecArg]
    call_args
                     saturating_call_args :: [SpecArg]
    saturating_call_args = [SpecArg]
    call_args [SpecArg] -> [SpecArg] -> [SpecArg]
    forall a. [a] -> [a] -> [a]
    ++ (Id -> SpecArg) -> [Id] -> [SpecArg]
    forall a b. (a -> b) -> [a] -> [b]
    map Id -> SpecArg
    mk_extra_dfun_arg ([SpecArg] -> [Id] -> [Id]
    forall b a. [b] -> [a] -> [a]
    dropList [SpecArg]
    call_args [Id]
    rhs_bndrs)
                     mk_extra_dfun_arg :: Id -> SpecArg
    mk_extra_dfun_arg Id
    bndr | Id -> Bool
    isTyVar Id
    bndr = SpecArg
    UnspecType
                                            | Bool
    otherwise = SpecArg
    UnspecArg

               ; ( useful, rhs_env2, leftover_bndrs
                 , rule_bndrs, rule_lhs_args
                 , spec_bndrs1, dx_binds, spec_args) <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    specHeader SpecEnv
    env [Id]
    rhs_bndrs [SpecArg]
    all_call_args

    --           ; pprTrace "spec_call" (vcat
    --                [ text "fun:       "  <+> ppr fn
    --                , text "call info: "  <+> ppr _ci
    --                , text "useful:    "  <+> ppr useful
    --                , text "rule_bndrs:"  <+> ppr rule_bndrs
    --                , text "lhs_args:  "  <+> ppr rule_lhs_args
    --                , text "spec_bndrs1:" <+> ppr spec_bndrs1
    --                , text "leftover_bndrs:" <+> pprIds leftover_bndrs
    --                , text "spec_args: "  <+> ppr spec_args
    --                , text "dx_binds:  "  <+> ppr dx_binds
    --                , text "rhs_bndrs"     <+> ppr rhs_bndrs
    --                , text "rhs_body"     <+> ppr rhs_body
    --                , text "rhs_env2:  "  <+> ppr (se_subst rhs_env2)
    --                , ppr dx_binds ]) $
    --             return ()

               ; if not useful  -- No useful specialisation
                    || already_covered rhs_env2 rules_acc rule_lhs_args
                 then return spec_acc
                 else
            do { -- Run the specialiser on the specialised RHS
                 -- The "1" suffix is before we maybe add the void arg
               ; (rhs_body', rhs_uds) <- specExpr rhs_env2 rhs_body
                    -- Add the { d1' = dx1; d2' = dx2 } usage stuff
                    -- to the rhs_uds; see Note [Specialising Calls]
               ; let rhs_uds_w_dx   = [DictBind]
    dx_binds [DictBind] -> UsageDetails -> UsageDetails
    `consDictBinds` UsageDetails
    rhs_uds
                     spec_rhs_bndrs = [Id]
    spec_bndrs1 [Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    ++ [Id]
    leftover_bndrs
                     (spec_uds, dumped_dbs) = dumpUDs spec_rhs_bndrs rhs_uds_w_dx
                     spec_rhs1 = [Id] -> OutExpr -> OutExpr
    forall b. [b] -> Expr b -> Expr b
    mkLams [Id]
    spec_rhs_bndrs (OutExpr -> OutExpr) -> OutExpr -> OutExpr
    forall a b. (a -> b) -> a -> b
    $
                                 OrdList DictBind -> OutExpr -> OutExpr
    wrapDictBindsE OrdList DictBind
    dumped_dbs OutExpr
    rhs_body'

                     spec_fn_ty1 = HasDebugCallStack => OutExpr -> Kind
    OutExpr -> Kind
    exprType OutExpr
    spec_rhs1

                     -- Maybe add a void arg to the specialised function,
                     -- to avoid unlifted bindings
                     -- See Note [Specialisations Must Be Lifted]
                     -- C.f. GHC.Core.Opt.WorkWrap.Utils.needsVoidWorkerArg
                     add_void_arg = HasDebugCallStack => Kind -> Bool
    Kind -> Bool
    isUnliftedType Kind
    spec_fn_ty1 Bool -> Bool -> Bool
    && Bool -> Bool
    not (Id -> Bool
    isJoinId Id
    fn)
                     (spec_bndrs, spec_rhs, spec_fn_ty)
                       | add_void_arg = ( voidPrimId : spec_bndrs1
                                        , Lam voidArgId spec_rhs1
                                        , mkVisFunTyMany unboxedUnitTy spec_fn_ty1)
                       | otherwise   = (spec_bndrs1, spec_rhs1, spec_fn_ty1)

                     join_arity_decr = [OutExpr] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [OutExpr]
    rule_lhs_args Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - [Id] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [Id]
    spec_bndrs

                     --------------------------------------
                     -- Add a suitable unfolding; see Note [Inline specialisations]
                     -- The wrap_unf_body applies the original unfolding to the specialised
                     -- arguments, not forgetting to wrap the dx_binds around the outside (#22358)
                     simpl_opts = DynFlags -> SimpleOpts
    initSimpleOpts DynFlags
    dflags
                     wrap_unf_body OutExpr
    body = (DictBind -> OutExpr -> OutExpr)
    -> OutExpr -> [DictBind] -> OutExpr
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (InBind -> OutExpr -> OutExpr
    forall b. Bind b -> Expr b -> Expr b
    Let (InBind -> OutExpr -> OutExpr)
    -> (DictBind -> InBind) -> DictBind -> OutExpr -> OutExpr
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictBind -> InBind
    db_bind) (OutExpr
    body OutExpr -> [OutExpr] -> OutExpr
    forall b. Expr b -> [Expr b] -> Expr b
    `mkApps` [OutExpr]
    spec_args) [DictBind]
    dx_binds
                     spec_unf = SimpleOpts
    -> [Id]
    -> (OutExpr -> OutExpr)
    -> [OutExpr]
    -> Unfolding
    -> Unfolding
    specUnfolding SimpleOpts
    simpl_opts [Id]
    spec_bndrs OutExpr -> OutExpr
    wrap_unf_body
                                              [OutExpr]
    rule_lhs_args Unfolding
    fn_unf

                     --------------------------------------
                     -- Adding arity information just propagates it a bit faster
                     --      See Note [Arity decrease] in GHC.Core.Opt.Simplify
                     -- Copy InlinePragma information from the parent Id.
                     -- So if f has INLINE[1] so does spec_fn
                     arity_decr     = (OutExpr -> Bool) -> [OutExpr] -> Int
    forall a. (a -> Bool) -> [a] -> Int
    count OutExpr -> Bool
    forall b. Expr b -> Bool
    isValArg [OutExpr]
    rule_lhs_args Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - (Id -> Bool) -> [Id] -> Int
    forall a. (a -> Bool) -> [a] -> Int
    count Id -> Bool
    isId [Id]
    spec_bndrs

                     spec_inl_prag
                       | Bool -> Bool
    not Bool
    is_local     -- See Note [Specialising imported functions]
                       , OccInfo -> Bool
    isStrongLoopBreaker (Id -> OccInfo
    idOccInfo Id
    fn) -- in GHC.Core.Opt.OccurAnal
                       = InlinePragma
    neverInlinePragma
                       | Bool
    otherwise
                       = InlinePragma
    inl_prag

                     spec_fn_info
                       = IdInfo
    vanillaIdInfo IdInfo -> Int -> IdInfo
    `setArityInfo`      Int -> Int -> Int
    forall a. Ord a => a -> a -> a
    max Int
    0 (Int
    fn_arity Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    arity_decr)
                                       IdInfo -> InlinePragma -> IdInfo
    `setInlinePragInfo` InlinePragma
    spec_inl_prag
                                       IdInfo -> Unfolding -> IdInfo
    `setUnfoldingInfo`  Unfolding
    spec_unf

                     -- Compute the IdDetails of the specialise Id
                     -- See Note [Transfer IdDetails during specialisation]
                     spec_fn_details
                       = case Id -> IdDetails
    idDetails Id
    fn of
                           JoinId Int
    join_arity Maybe [CbvMark]
    _ -> Int -> Maybe [CbvMark] -> IdDetails
    JoinId (Int
    join_arity Int -> Int -> Int
    forall a. Num a => a -> a -> a
    - Int
    join_arity_decr) Maybe [CbvMark]
    forall a. Maybe a
    Nothing
                           DFunId Bool
    is_nt        -> Bool -> IdDetails
    DFunId Bool
    is_nt
                           IdDetails
    _                   -> IdDetails
    VanillaId

               ; spec_fn <- newSpecIdSM (idName fn) spec_fn_ty spec_fn_details spec_fn_info
               ; let
                    -- The rule to put in the function's specialisation is:
                    --      forall x @b d1' d2'.
                    --          f x @T1 @b @T2 d1' d2' = f1 x @b
                    -- See Note [Specialising Calls]
                    herald | Bool
    spec_imp  = -- Specialising imported fn
                                         String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SPEC/" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <> Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    this_mod
                           | Bool
    otherwise = -- Specialising local fn
                                         String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SPEC"

                    spec_rule = DynFlags
    -> Module
    -> Bool
    -> Activation
    -> SDoc
    -> Id
    -> [Id]
    -> [OutExpr]
    -> OutExpr
    -> CoreRule
    mkSpecRule DynFlags
    dflags Module
    this_mod Bool
    True Activation
    inl_act
                                        SDoc
    herald Id
    fn [Id]
    rule_bndrs [OutExpr]
    rule_lhs_args
                                        (OutExpr -> [Id] -> OutExpr
    forall b. Expr b -> [Id] -> Expr b
    mkVarApps (Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    spec_fn) [Id]
    spec_bndrs)

                    spec_f_w_arity = Id
    spec_fn

                    _rule_trace_doc = [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc
    dcolon SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    fn_type
                                           , Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    spec_fn  SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc
    dcolon SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    spec_fn_ty
                                           , [Id] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [Id]
    rhs_bndrs, [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    call_args
                                           , CoreRule -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CoreRule
    spec_rule
                                           ]

               ; -- pprTrace "spec_call: rule" _rule_trace_doc
                 return ( spec_rule                  : rules_acc
                        , (spec_f_w_arity, spec_rhs) : pairs_acc
                        , spec_uds           `thenUDs` uds_acc
                        ) } }

    -- Convenience function for invoking lookupRule from Specialise
    -- The SpecEnv's InScopeSet should include all the Vars in the [CoreExpr]
    specLookupRule :: SpecEnv -> Id -> [CoreExpr]
                   -> CompilerPhase  -- Look up rules as if we were in this phase
                   -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
    specLookupRule :: SpecEnv
    -> Id
    -> [OutExpr]
    -> CompilerPhase
    -> [CoreRule]
    -> Maybe (CoreRule, OutExpr)
    specLookupRule SpecEnv
    env Id
    fn [OutExpr]
    args CompilerPhase
    phase [CoreRule]
    rules
      = RuleOpts
    -> InScopeEnv
    -> (Activation -> Bool)
    -> Id
    -> [OutExpr]
    -> [CoreRule]
    -> Maybe (CoreRule, OutExpr)
    lookupRule RuleOpts
    ropts InScopeEnv
    in_scope_env Activation -> Bool
    is_active Id
    fn [OutExpr]
    args [CoreRule]
    rules
      where
        dflags :: DynFlags
    dflags       = SpecEnv -> DynFlags
    se_dflags SpecEnv
    env
        in_scope :: InScopeSet
    in_scope     = Subst -> InScopeSet
    getSubstInScope (SpecEnv -> Subst
    se_subst SpecEnv
    env)
        in_scope_env :: InScopeEnv
    in_scope_env = InScopeSet -> (Id -> Unfolding) -> InScopeEnv
    ISE InScopeSet
    in_scope ((Activation -> Bool) -> Id -> Unfolding
    whenActiveUnfoldingFun Activation -> Bool
    is_active)
        ropts :: RuleOpts
    ropts        = DynFlags -> RuleOpts
    initRuleOpts DynFlags
    dflags
        is_active :: Activation -> Bool
    is_active    = CompilerPhase -> Activation -> Bool
    isActive CompilerPhase
    phase

    {- Note [Specialising DFuns]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    DFuns have a special sort of unfolding (DFunUnfolding), and it is
    hard to specialise a DFunUnfolding to give another DFunUnfolding
    unless the DFun is fully applied (#18120).  So, in the case of DFunIds
    we simply extend the CallKey with trailing UnspecTypes/UnspecArgs,
    so that we'll generate a rule that completely saturates the DFun.

    There is an ASSERT that checks this, in the DFunUnfolding case of
    GHC.Core.Unfold.Make.specUnfolding.

    Note [Transfer IdDetails during specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising a function, `newSpecIdSM` comes up with a fresh Id the
    specialised RHS will be bound to. It is critical that we get the `IdDetails` of
    the specialised Id correct:

    * JoinId: We want the specialised Id to be a join point, too.  But
      we have to carefully adjust the arity

    * DFunId: It is crucial that we also make the new Id a DFunId.
      - First, because it obviously /is/ a DFun, having a DFunUnfolding and
        all that; see Note [Specialising DFuns]

      - Second, DFuns get very delicate special treatment in the demand analyser;
        see GHC.Core.Opt.DmdAnal.enterDFun.  If the specialised function isn't
        also a DFunId, this special treatment doesn't happen, so the demand
        analyser makes a too-strict DFun, and we get an infinite loop.  See Note
        [Do not strictify a DFun's parameter dictionaries] in GHC.Core.Opt.DmdAnal.
        #22549 describes the loop, and (lower down) a case where a /specialised/
        DFun caused a loop.

    * WorkerLikeId: Introduced by WW, so after Specialise. Nevertheless, they come
      up when specialising imports. We must keep them as VanillaIds because WW
      will detect them as WorkerLikeIds again. That is, unless specialisation
      allows unboxing of all previous CBV args, in which case sticking to
      VanillaIds was the only correct choice to begin with.

    * RecSelId, DataCon*Id, ClassOpId, PrimOpId, FCallId, CoVarId, TickBoxId:
      Never specialised.

    Note [Specialisation Must Preserve Sharing]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a function:

        f :: forall a. Eq a => a -> blah
        f =
          if expensive
             then f1
             else f2

    As written, all calls to 'f' will share 'expensive'. But if we specialise 'f'
    at 'Int', eg:

        $sfInt = SUBST[a->Int,dict->dEqInt] (if expensive then f1 else f2)

        RULE "SPEC f"
          forall (d :: Eq Int).
            f Int _ = $sfIntf

    We've now lost sharing between 'f' and '$sfInt' for 'expensive'. Yikes!

    To avoid this, we only generate specialisations for functions whose arity is
    enough to bind all of the arguments we need to specialise.  This ensures our
    specialised functions don't do any work before receiving all of their dicts,
    and thus avoids the 'f' case above.

    Note [Specialisations Must Be Lifted]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a function 'f':

        f = forall a. Eq a => Array# a

    used like

        case x of
          True -> ...f @Int dEqInt...
          False -> 0

    Naively, we might generate an (expensive) specialisation

        $sfInt :: Array# Int

    even in the case that @x = False@! Instead, we add a dummy 'Void#' argument to
    the specialisation '$sfInt' ($sfInt :: Void# -> Array# Int) in order to
    preserve laziness.

    Note [Care with unlifted bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider (#22998)
        f x = let x::ByteArray# = <some literal>
                  n::Natural    = NB x
              in wombat @192827 (n |> co)
    where
      co :: Natural ~ KnownNat 192827
      wombat :: forall (n:Nat). KnownNat n => blah

    Left to itself, the specialiser would float the bindings for `x` and `n` to top
    level, so we can specialise `wombat`.  But we can't have a top-level ByteArray#
    (see Note [Core letrec invariant] in GHC.Core).  Boo.

    This is pretty exotic, so we take a simple way out: in specBind (the NonRec
    case) do not float the binding itself unless it satisfies exprIsTopLevelBindable.
    This is conservative: maybe the RHS of `x` has a free var that would stop it
    floating to top level anyway; but that is hard to spot (since we don't know what
    the non-top-level in-scope binders are) and rare (since the binding must satisfy
    Note [Core let-can-float invariant] in GHC.Core).

    Note [Specialising Calls]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we have a function with a complicated type:

        f :: forall a b c. Int -> Eq a => Show b => c -> Blah
        f @a @b @c i dEqA dShowA x = blah

    and suppose it is called at:

        f 7 @T1 @T2 @T3 dEqT1 ($dfShow dShowT2) t3

    This call is described as a 'CallInfo' whose 'ci_key' is:

        [ SpecType T1, SpecType T2, UnspecType, UnspecArg, SpecDict dEqT1
        , SpecDict ($dfShow dShowT2), UnspecArg ]

    Why are 'a' and 'b' identified as 'SpecType', while 'c' is 'UnspecType'?
    Because we must specialise the function on type variables that appear
    free in its *dictionary* arguments; but not on type variables that do not
    appear in any dictionaries, i.e. are fully polymorphic.

    Because this call has dictionaries applied, we'd like to specialise
    the call on any type argument that appears free in those dictionaries.
    In this case, those are [a :-> T1, b :-> T2].

    We also need to substitute the dictionary binders with their
    specialised dictionaries. The simplest substitution would be
    [dEqA :-> dEqT1, dShowA :-> $dfShow dShowT2], but this duplicates
    work, since `$dfShow dShowT2` is a function application. Therefore, we
    also want to *float the dictionary out* (via bindAuxiliaryDict),
    creating a new dict binding

        dShow1 = $dfShow dShowT2

    and the substitution [dEqA :-> dEqT1, dShowA :-> dShow1].

    With the substitutions in hand, we can generate a specialised function:

        $sf :: forall c. Int -> c -> Blah
        $sf = SUBST[a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowA :-> dShow1] (\@c i x -> blah)

    Note that the substitution is applied to the whole thing.  This is
    convenient, but just slightly fragile.  Notably:
      * There had better be no name clashes in a/b/c

    We must construct a rewrite rule:

        RULE "SPEC f @T1 @T2 _"
          forall (@c :: Type) (i :: Int) (d1 :: Eq T1) (d2 :: Show T2).
            f @T1 @T2 @c i d1 d2 = $sf @c i

    In the rule, d1 and d2 are just wildcards, not used in the RHS.  Note
    additionally that 'x' isn't captured by this rule --- we bind only
    enough etas in order to capture all of the *specialised* arguments.

    Note [Drop dead args from specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising a function, it’s possible some of the arguments may
    actually be dead. For example, consider:

        f :: forall a. () -> Show a => a -> String
        f x y = show y ++ "!"

    We might generate the following CallInfo for `f @Int`:

        [SpecType Int, UnspecArg, SpecDict $dShowInt, UnspecArg]

    Normally we’d include both the x and y arguments in the
    specialisation, since we’re not specialising on either of them. But
    that’s silly, since x is actually unused! So we might as well drop it
    in the specialisation:

        $sf :: Int -> String
        $sf y = show y ++ "!"

        {-# RULE "SPEC f @Int" forall x. f @Int x $dShow = $sf #-}

    This doesn’t save us much, since the arg would be removed later by
    worker/wrapper, anyway, but it’s easy to do.

    Wrinkles

    * Note that we only drop dead arguments if:
        1. We don’t specialise on them.
        2. They come before an argument we do specialise on.
      Doing the latter would require eta-expanding the RULE, which could
      make it match less often, so it’s not worth it. Doing the former could
      be more useful --- it would stop us from generating pointless
      specialisations --- but it’s more involved to implement and unclear if
      it actually provides much benefit in practice.

    * If the function has a stable unfolding, specHeader has to come up with
      arguments to pass to that stable unfolding, when building the stable
      unfolding of the specialised function: this is the last field in specHeader's
      big result tuple.

      The right thing to do is to produce a LitRubbish; it should rapidly
      disappear.  Rather like GHC.Core.Opt.WorkWrap.Utils.mk_absent_let.

    Note [Specialisation modulo dictionary selectors]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In #19644, we discovered that the ClassOp/DFun rules from
    Note [ClassOp/DFun selection] inhibit transitive specialisation.
    Example, inspired by T17966:

      class C a where
        m :: Show b => a -> b -> String
        dummy :: a -> () -- Force a datatype dictionary representation

      instance C Int where
        m a b = show a ++ show b
        dummy _ = ()

      f :: (C a, Show b) => a -> b -> String
      f a b = m a b ++ "!"
      {-# INLINABLE[0] f #-}

      main = putStrLn (f (42::Int) (True::Bool))

    Here, we specialise `f` at `Int` and `Bool`, giving

      $dC = $fCInt
      $dShow = GHC.Show.$fShowBool
      $sf (a::Int) (b::Bool) =
            ... (m @Int $dC @Bool $dShow a b) ...

    Here `m` is just a DictSel, so there is (apparently) nothing to specialise!
    However, the next Simplifier run will expose the rewritten instance method:

      ... $fCInt_$cm @Bool $fShowBool a b ...

    where $fCInt_$cm is the instance method for `m` in `instance C Int`:

       $fCInt_$cm :: forall b. Show b => Int -> b -> String
       $fCInt_$cm b d x y = show @Int $dShowInt x ++ show @b d y

    We want to specialise this! How? By doing the method-selection rewrite in
    the Specialiser. Hence

    1. In the App case of 'specExpr', try to apply the ClassOp/DFun rule on the
       head of the application, repeatedly, via 'fireRewriteRules'.
    2. Attach an unfolding to freshly-bound dictionary ids such as `$dC` and
       `$dShow` in `bindAuxiliaryDict`, so that we can exploit the unfolding
       in 'fireRewriteRules' to do the ClassOp/DFun rewrite.

    NB: Without (2), (1) would be pointless, because 'lookupRule' wouldn't be able
    to look into the RHS of `$dC` to see the DFun.

    Note [Zap occ info in rule binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we generate a specialisation RULE, we need to drop occurrence
    info on the binders. If we don’t, things go wrong when we specialise a
    function like

        f :: forall a. () -> Show a => a -> String
        f x y = show y ++ "!"

    since we’ll generate a RULE like

        RULE "SPEC f @Int" forall x [Occ=Dead].
          f @Int x $dShow = $sf

    and Core Lint complains, even though x only appears on the LHS (due to
    Note [Drop dead args from specialisations]).

    Why is that a Lint error? Because the arguments on the LHS of a rule
    are syntactically expressions, not patterns, so Lint treats the
    appearance of x as a use rather than a binding. Fortunately, the
    solution is simple: we just make sure to zap the occ info before
    using ids as wildcard binders in a rule.

    Note [Account for casts in binding]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
       f :: Eq a => a -> IO ()
       {-# INLINABLE f
           StableUnf = (/\a \(d:Eq a) (x:a). blah) |> g
         #-}
       f = ...

    In f's stable unfolding we have done some modest simplification which
    has pushed the cast to the outside.  (I wonder if this is the Right
    Thing, but it's what happens now; see GHC.Core.Opt.Simplify.Utils Note [Casts and
    lambdas].)  Now that stable unfolding must be specialised, so we want
    to push the cast back inside. It would be terrible if the cast
    defeated specialisation!  Hence the use of collectBindersPushingCo.

    Note [Evidence foralls]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose (#12212) that we are specialising
       f :: forall a b. (Num a, F a ~ F b) => blah
    with a=b=Int. Then the RULE will be something like
       RULE forall (d:Num Int) (g :: F Int ~ F Int).
            f Int Int d g = f_spec
    But both varToCoreExpr (when constructing the LHS args), and the
    simplifier (when simplifying the LHS args), will transform to
       RULE forall (d:Num Int) (g :: F Int ~ F Int).
            f Int Int d <F Int> = f_spec
    by replacing g with Refl.  So now 'g' is unbound, which results in a later
    crash. So we use Refl right off the bat, and do not forall-quantify 'g':
     * varToCoreExpr generates a Refl
     * exprsFreeIdsList returns the Ids bound by the args,
       which won't include g

    You might wonder if this will match as often, but the simplifier replaces
    complicated Refl coercions with Refl pretty aggressively.

    Note [Orphans and auto-generated rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we specialise an INLINABLE function, or when we have
    -fspecialise-aggressively, we auto-generate RULES that are orphans.
    We don't want to warn about these, or we'd generate a lot of warnings.
    Thus, we only warn about user-specified orphan rules.

    Indeed, we don't even treat the module as an orphan module if it has
    auto-generated *rule* orphans.  Orphan modules are read every time we
    compile, so they are pretty obtrusive and slow down every compilation,
    even non-optimised ones.  (Reason: for type class instances it's a
    type correctness issue.)  But specialisation rules are strictly for
    *optimisation* only so it's fine not to read the interface.

    What this means is that a SPEC rules from auto-specialisation in
    module M will be used in other modules only if M.hi has been read for
    some other reason, which is actually pretty likely.

    Note [From non-recursive to recursive]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Even in the non-recursive case, if any dict-binds depend on 'fn' we might
    have built a recursive knot

          f a d x = <blah>
          MkUD { ud_binds = NonRec d7  (MkD ..f..)
               , ud_calls = ...(f T d7)... }

    The we generate

         Rec { fs x = <blah>[T/a, d7/d]
               f a d x = <blah>
                   RULE f T _ = fs
               d7 = ...f... }

    Here the recursion is only through the RULE.

    However we definitely should /not/ make the Rec in this wildly common
    case:
          d = ...
          MkUD { ud_binds = NonRec d7 (...d...)
               , ud_calls = ...(f T d7)... }

    Here we want simply to add d to the floats, giving
          MkUD { ud_binds = NonRec d (...)
                            NonRec d7 (...d...)
               , ud_calls = ...(f T d7)... }

    In general, we need only make this Rec if
      - there are some specialisations (spec_binds non-empty)
      - there are some dict_binds that depend on f (dump_dbs non-empty)

    Note [Avoiding loops (DFuns)]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When specialising /dictionary functions/ we must be very careful to
    avoid building loops. Here is an example that bit us badly, on
    several distinct occasions.

    Here is one: #3591
         class Eq a => C a
         instance Eq [a] => C [a]

    This translates to
         dfun :: Eq [a] -> C [a]
         dfun a d = MkD a d (meth d)

         d4 :: Eq [T] = <blah>
         d2 ::  C [T] = dfun T d4
         d1 :: Eq [T] = $p1 d2
         d3 ::  C [T] = dfun T d1

    None of these definitions is recursive. What happened was that we
    generated a specialisation:
         RULE forall d. dfun T d = dT  :: C [T]
         dT = (MkD a d (meth d)) [T/a, d1/d]
            = MkD T d1 (meth d1)

    But now we use the RULE on the RHS of d2, to get
        d2 = dT = MkD d1 (meth d1)
        d1 = $p1 d2

    and now d1 is bottom!  The problem is that when specialising 'dfun' we
    should first dump "below" the binding all floated dictionary bindings
    that mention 'dfun' itself.  So d2 and d3 (and hence d1) must be
    placed below 'dfun', and thus unavailable to it when specialising
    'dfun'.  That in turn means that the call (dfun T d1) must be
    discarded.  On the other hand, the call (dfun T d4) is fine, assuming
    d4 doesn't mention dfun.

    Solution:
      Discard all calls that mention dictionaries that depend
      (directly or indirectly) on the dfun we are specialising.
      This is done by 'filterCalls'

    Note [Avoiding loops (non-DFuns)]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The whole Note [Avoiding loops (DFuns)] things applies only to DFuns.
    It's important /not/ to apply filterCalls to non-DFuns. For example:

      class C a where { foo,bar :: [a] -> [a] }

      instance C Int where
         foo x = r_bar x
         bar xs = reverse xs

      r_bar :: C a => [a] -> [a]
      r_bar xs = bar (xs ++ xs)

    That translates to:

        r_bar a (c::C a) (xs::[a]) = bar a d (xs ++ xs)

        Rec { $fCInt :: C Int = MkC foo_help reverse
              foo_help (xs::[Int]) = r_bar Int $fCInt xs }

    The call (r_bar $fCInt) mentions $fCInt,
                            which mentions foo_help,
                            which mentions r_bar

    But we DO want to specialise r_bar at Int:
        Rec { $fCInt :: C Int = MkC foo_help reverse
              foo_help (xs::[Int]) = r_bar Int $fCInt xs

              r_bar a (c::C a) (xs::[a]) = bar a d (xs ++ xs)
                RULE r_bar Int _ = r_bar_Int

              r_bar_Int xs = bar Int $fCInt (xs ++ xs)
               }

    Note that, because of its RULE, r_bar joins the recursive
    group.  (In this case it'll unravel a short moment later.)
    See test simplCore/should_compile/T19599a.

    Another example is #19599, which looked like this:

       class (Show a, Enum a) => MyShow a where
          myShow :: a -> String

       myShow_impl :: MyShow a => a -> String

       foo :: Int -> String
       foo = myShow_impl @Int $fMyShowInt

       Rec { $fMyShowInt = MkMyShowD $fEnumInt $fShowInt $cmyShow
           ; $cmyShow = myShow_impl @Int $fMyShowInt }

    Here, we really do want to specialise `myShow_impl @Int $fMyShowInt`.

    Note [Specialising a recursive group]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
        let rec { f x = ...g x'...
                ; g y = ...f y'.... }
        in f 'a'
    Here we specialise 'f' at Char; but that is very likely to lead to
    a specialisation of 'g' at Char.  We must do the latter, else the
    whole point of specialisation is lost.

    But we do not want to keep iterating to a fixpoint, because in the
    presence of polymorphic recursion we might generate an infinite number
    of specialisations.

    So we use the following heuristic:
      * Arrange the rec block in dependency order, so far as possible
        (the occurrence analyser already does this)

      * Specialise it much like a sequence of lets

      * Then go through the block a second time, feeding call-info from
        the RHSs back in the bottom, as it were

    In effect, the ordering maxmimises the effectiveness of each sweep,
    and we do just two sweeps.   This should catch almost every case of
    monomorphic recursion -- the exception could be a very knotted-up
    recursion with multiple cycles tied up together.

    This plan is implemented in the Rec case of specBindItself.

    Note [Specialisations already covered]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We obviously don't want to generate two specialisations for the same
    argument pattern.  There are two wrinkles

    1. We do the already-covered test in specDefn, not when we generate
    the CallInfo in mkCallUDs.  We used to test in the latter place, but
    we now iterate the specialiser somewhat, and the Id at the call site
    might therefore not have all the RULES that we can see in specDefn

    2. What about two specialisations where the second is an *instance*
    of the first?  If the more specific one shows up first, we'll generate
    specialisations for both.  If the *less* specific one shows up first,
    we *don't* currently generate a specialisation for the more specific
    one.  (See the call to lookupRule in already_covered.)  Reasons:
      (a) lookupRule doesn't say which matches are exact (bad reason)
      (b) if the earlier specialisation is user-provided, it's
          far from clear that we should auto-specialise further

    Note [Auto-specialisation and RULES]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider:
       g :: Num a => a -> a
       g = ...

       f :: (Int -> Int) -> Int
       f w = ...
       {-# RULE f g = 0 #-}

    Suppose that auto-specialisation makes a specialised version of
    g::Int->Int. That version won't appear in the LHS of the RULE for f.
    So if the specialisation rule fires too early, the rule for f may
    never fire.

    It might be possible to add new rules, to "complete" the rewrite system.
    Thus when adding
            RULE forall d. g Int d = g_spec
    also add
            RULE f g_spec = 0

    But that's a bit complicated.  For now we ask the programmer's help,
    by *copying the INLINE activation pragma* to the auto-specialised
    rule.  So if g says {-# NOINLINE[2] g #-}, then the auto-spec rule
    will also not be active until phase 2.  And that's what programmers
    should jolly well do anyway, even aside from specialisation, to ensure
    that g doesn't inline too early.

    This in turn means that the RULE would never fire for a NOINLINE
    thing so not much point in generating a specialisation at all.

    Note [Specialisation shape]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We only specialise a function if it has visible top-level lambdas
    corresponding to its overloading.  E.g. if
            f :: forall a. Eq a => ....
    then its body must look like
            f = /\a. \d. ...

    Reason: when specialising the body for a call (f ty dexp), we want to
    substitute dexp for d, and pick up specialised calls in the body of f.

    We do allow casts, however; see Note [Account for casts in binding].

    This doesn't always work.  One example I came across was this:
            newtype Gen a = MkGen{ unGen :: Int -> a }

            choose :: Eq a => a -> Gen a
            choose n = MkGen (\r -> n)

            oneof = choose (1::Int)

    It's a silly example, but we get
            choose = /\a. g `cast` co
    where choose doesn't have any dict arguments.  Thus far I have not
    tried to fix this (wait till there's a real example).

    Mind you, then 'choose' will be inlined (since RHS is trivial) so
    it doesn't matter.  This comes up with single-method classes

       class C a where { op :: a -> a }
       instance C a => C [a] where ....
    ==>
       $fCList :: C a => C [a]
       $fCList = $copList |> (...coercion>...)
       ....(uses of $fCList at particular types)...

    So we suppress the WARN if the rhs is trivial.

    Note [Inline specialisations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Here is what we do with the InlinePragma of the original function

      * Activation/RuleMatchInfo: both inherited from the original function

      * InlineSpec: inherit from original function

      * Unfolding: transfer a StableUnfolding iff it is UnfWhen
                   See GHC.Core.Unfold.Make.specUnfolding
                   and its Note [Specialising unfoldings]

    InlineSpec: you might wonder why we specialise INLINE functions at all.
    After all they should be inlined, right?  Two reasons:

     * Even INLINE functions are sometimes not inlined, when they aren't
       applied to interesting arguments.  But perhaps the type arguments
       alone are enough to specialise (even though the args are too boring
       to trigger inlining), and it's certainly better to call the
       specialised version.

     * The RHS of an INLINE function might call another overloaded function,
       and we'd like to generate a specialised version of that function too.
       This actually happens a lot. Consider
          replicateM_ :: (Monad m) => Int -> m a -> m ()
          {-# INLINABLE replicateM_ #-}
          replicateM_ d x ma = ...
       The strictness analyser may transform to
          replicateM_ :: (Monad m) => Int -> m a -> m ()
          {-# INLINE replicateM_ #-}
          replicateM_ d x ma = case x of I# x' -> $wreplicateM_ d x' ma

          $wreplicateM_ :: (Monad m) => Int# -> m a -> m ()
          {-# INLINABLE $wreplicateM_ #-}
          $wreplicateM_ = ...
       Now an importing module has a specialised call to replicateM_, say
       (replicateM_ dMonadIO).  We certainly want to specialise $wreplicateM_!
       This particular example had a huge effect on the call to replicateM_
       in nofib/shootout/n-body.
    -}

    {- *********************************************************************
    *                                                                      *
                       SpecArg, and specHeader
    *                                                                      *
    ********************************************************************* -}

    -- | An argument that we might want to specialise.
    -- See Note [Specialising Calls] for the nitty gritty details.
    data SpecArg
      =
        -- | Type arguments that should be specialised, due to appearing
        -- free in the type of a 'SpecDict'.
        SpecType Type

        -- | Type arguments that should remain polymorphic.
      | UnspecType

        -- | Dictionaries that should be specialised. mkCallUDs ensures
        -- that only "interesting" dictionary arguments get a SpecDict;
        -- see Note [Interesting dictionary arguments]
      | SpecDict DictExpr

        -- | Value arguments that should not be specialised.
      | UnspecArg

    instance Outputable SpecArg where
      ppr :: SpecArg -> SDoc
    ppr (SpecType Kind
    t) = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SpecType" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Kind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Kind
    t
      ppr SpecArg
    UnspecType   = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "UnspecType"
      ppr (SpecDict OutExpr
    d) = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "SpecDict" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> OutExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutExpr
    d
      ppr SpecArg
    UnspecArg    = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "UnspecArg"

    specArgFreeIds :: SpecArg -> IdSet
    specArgFreeIds :: SpecArg -> VarSet
    specArgFreeIds (SpecType {}) = VarSet
    emptyVarSet
    specArgFreeIds (SpecDict OutExpr
    dx) = OutExpr -> VarSet
    exprFreeIds OutExpr
    dx
    specArgFreeIds SpecArg
    UnspecType    = VarSet
    emptyVarSet
    specArgFreeIds SpecArg
    UnspecArg     = VarSet
    emptyVarSet

    specArgFreeVars :: SpecArg -> VarSet
    specArgFreeVars :: SpecArg -> VarSet
    specArgFreeVars (SpecType Kind
    ty) = Kind -> VarSet
    tyCoVarsOfType Kind
    ty
    specArgFreeVars (SpecDict OutExpr
    dx) = OutExpr -> VarSet
    exprFreeVars OutExpr
    dx
    specArgFreeVars SpecArg
    UnspecType    = VarSet
    emptyVarSet
    specArgFreeVars SpecArg
    UnspecArg     = VarSet
    emptyVarSet

    isSpecDict :: SpecArg -> Bool
    isSpecDict :: SpecArg -> Bool
    isSpecDict (SpecDict {}) = Bool
    True
    isSpecDict SpecArg
    _             = Bool
    False

    -- | Given binders from an original function 'f', and the 'SpecArg's
    -- corresponding to its usage, compute everything necessary to build
    -- a specialisation.
    --
    -- We will use the running example from Note [Specialising Calls]:
    --
    --     f :: forall a b c. Int -> Eq a => Show b => c -> Blah
    --     f @a @b @c i dEqA dShowB x = blah
    --
    -- Suppose we decide to specialise it at the following pattern:
    --
    --     [ SpecType T1, SpecType T2, UnspecType, UnspecArg
    --     , SpecDict dEqT1, SpecDict ($dfShow dShowT2), UnspecArg ]
    --
    -- We'd eventually like to build the RULE
    --
    --     RULE "SPEC f @T1 @T2 _"
    --       forall (@c :: Type) (i :: Int) (d1 :: Eq T1) (d2 :: Show T2).
    --         f @T1 @T2 @c i d1 d2 = $sf @c i
    --
    -- and the specialisation '$sf'
    --
    --     $sf :: forall c. Int -> c -> Blah
    --     $sf = SUBST[a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowB :-> dShow1] (\@c i x -> blah)
    --
    -- where dShow1 is a floated binding created by bindAuxiliaryDict.
    --
    -- The cases for 'specHeader' below are presented in the same order as this
    -- running example. The result of 'specHeader' for this example is as follows:
    --
    --    ( -- Returned arguments
    --      env + [a :-> T1, b :-> T2, dEqA :-> dEqT1, dShowB :-> dShow1]
    --    , [x]
    --
    --      -- RULE helpers
    --    , [c, i, d1, d2]
    --    , [T1, T2, c, i, d1, d2]
    --
    --      -- Specialised function helpers
    --    , [c, i, x]
    --    , [dShow1 = $dfShow dShowT2]
    --    , [T1, T2, c, i, dEqT1, dShow1]
    --    )
    specHeader
         :: SpecEnv
         -> [InBndr]    -- The binders from the original function 'f'
         -> [SpecArg]   -- From the CallInfo
         -> SpecM ( Bool     -- True <=> some useful specialisation happened
                             -- Not the same as any (isSpecDict args) because
                             -- the args might be longer than bndrs

                    -- Returned arguments
                  , SpecEnv      -- Substitution to apply to the body of 'f'
                  , [OutBndr]    -- Leftover binders from the original function 'f'
                                 --   that don’t have a corresponding SpecArg

                    -- RULE helpers
                  , [OutBndr]    -- Binders for the RULE
                  , [OutExpr]    -- Args for the LHS of the rule

                    -- Specialised function helpers
                  , [OutBndr]    -- Binders for $sf
                  , [DictBind]   -- Auxiliary dictionary bindings
                  , [OutExpr]    -- Specialised arguments for unfolding
                                 -- Same length as "Args for LHS of rule"
                  )

    -- We want to specialise on type 'T1', and so we must construct a substitution
    -- 'a->T1', as well as a LHS argument for the resulting RULE and unfolding
    -- details.
    specHeader :: SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecType Kind
    ty : [SpecArg]
    args)
      = do { -- Find qvars, the type variables to add to the binders for the rule
             -- Namely those free in `ty` that aren't in scope
             -- See (MP2) in Note [Specialising polymorphic dictionaries]
             let in_scope :: InScopeSet
    in_scope = Subst -> InScopeSet
    Core.getSubstInScope (SpecEnv -> Subst
    se_subst SpecEnv
    env)
                 qvars :: [Id]
    qvars    = [Id] -> [Id]
    scopedSort ([Id] -> [Id]) -> [Id] -> [Id]
    forall a b. (a -> b) -> a -> b
    $
                            (Id -> Bool) -> [Id] -> [Id]
    forall a. (a -> Bool) -> [a] -> [a]
    filterOut (Id -> InScopeSet -> Bool
    `elemInScopeSet` InScopeSet
    in_scope) ([Id] -> [Id]) -> [Id] -> [Id]
    forall a b. (a -> b) -> a -> b
    $
                            Kind -> [Id]
    tyCoVarsOfTypeList Kind
    ty
                 (SpecEnv
    env1, [Id]
    qvars') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    qvars
                 ty' :: Kind
    ty'            = SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env1 Kind
    ty
                 env2 :: SpecEnv
    env2           = SpecEnv -> Id -> Kind -> SpecEnv
    extendTvSubst SpecEnv
    env1 Id
    bndr Kind
    ty'
           ; (useful, env3, leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)
                <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    specHeader SpecEnv
    env2 [Id]
    bndrs [SpecArg]
    args
           ; pure ( useful
                  , env3
                  , leftover_bndrs
                  , qvars' ++ rule_bs
                  , Type ty' : rule_es
                  , qvars' ++ bs'
                  , dx
                  , Type ty' : spec_args
                  )
           }

    -- Next we have a type that we don't want to specialise. We need to perform
    -- a substitution on it (in case the type refers to 'a'). Additionally, we need
    -- to produce a binder, LHS argument and RHS argument for the resulting rule,
    -- /and/ a binder for the specialised body.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecArg
    UnspecType : [SpecArg]
    args)
      = do { let (SpecEnv
    env', Id
    bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    bndr
           ; (useful, env'', leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)
                <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args
           ; pure ( useful
                  , env''
                  , leftover_bndrs
                  , bndr' : rule_bs
                  , varToCoreExpr bndr' : rule_es
                  , bndr' : bs'
                  , dx
                  , varToCoreExpr bndr' : spec_args
                  )
           }

    -- Next we want to specialise the 'Eq a' dict away. We need to construct
    -- a wildcard binder to match the dictionary (See Note [Specialising Calls] for
    -- the nitty-gritty), as a LHS rule and unfolding details.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecDict OutExpr
    d : [SpecArg]
    args)
      | Bool -> Bool
    not (Id -> Bool
    isDeadBinder Id
    bndr)
      , (Id -> Bool) -> VarSet -> Bool
    allVarSet (Id -> InScopeSet -> Bool
    `elemInScopeSet` InScopeSet
    in_scope) (OutExpr -> VarSet
    exprFreeVars OutExpr
    d)
        -- See Note [Weird special case for SpecDict]
      = do { (env1, bndr') <- SpecEnv -> Id -> UniqSM (SpecEnv, Id)
    newDictBndr SpecEnv
    env Id
    bndr -- See Note [Zap occ info in rule binders]
           ; let (env2, dx_bind, spec_dict) = bindAuxiliaryDict env1 bndr bndr' d
           ; (_, env3, leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)
                 <- specHeader env2 bndrs args
           ; pure ( True      -- Ha!  A useful specialisation!
                  , env3
                  , leftover_bndrs
                  -- See Note [Evidence foralls]
                  , exprFreeIdsList (varToCoreExpr bndr') ++ rule_bs
                  , varToCoreExpr bndr' : rule_es
                  , bs'
                  , maybeToList dx_bind ++ dx
                  , spec_dict : spec_args
                  )
           }
       where
         in_scope :: InScopeSet
    in_scope = Subst -> InScopeSet
    Core.getSubstInScope (SpecEnv -> Subst
    se_subst SpecEnv
    env)

    -- Finally, we don't want to specialise on this argument 'i':
    --   - It's an UnSpecArg, or
    --   - It's a dead dictionary
    -- We need to produce a binder, LHS and RHS argument for the RULE, and
    -- a binder for the specialised body.
    --
    -- NB: Calls to 'specHeader' will trim off any trailing 'UnspecArg's, which is
    -- why 'i' doesn't appear in our RULE above. But we have no guarantee that
    -- there aren't 'UnspecArg's which come /before/ all of the dictionaries, so
    -- this case must be here.
    specHeader SpecEnv
    env (Id
    bndr : [Id]
    bndrs) (SpecArg
    _ : [SpecArg]
    args)
        -- The "_" can be UnSpecArg, or SpecDict where the bndr is dead
      = do { -- see Note [Zap occ info in rule binders]
             let (SpecEnv
    env', Id
    bndr') = SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env (Id -> Id
    zapIdOccInfo Id
    bndr)
           ; (useful, env'', leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)
                 <- SpecEnv
    -> [Id]
    -> [SpecArg]
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    specHeader SpecEnv
    env' [Id]
    bndrs [SpecArg]
    args

           ; let bndr_ty = Id -> Kind
    idType Id
    bndr'

                 -- See Note [Drop dead args from specialisations]
                 -- C.f. GHC.Core.Opt.WorkWrap.Utils.mk_absent_let
                 (mb_spec_bndr, spec_arg)
                    | isDeadBinder bndr
                    , Just lit_expr <- mkLitRubbish bndr_ty
                    = (Nothing, lit_expr)
                    | otherwise
                    = (Just bndr', varToCoreExpr bndr')

           ; pure ( useful
                  , env''
                  , leftover_bndrs
                  , bndr' : rule_bs
                  , varToCoreExpr bndr' : rule_es
                  , case mb_spec_bndr of
                      Just Id
    b' -> Id
    b' Id -> [Id] -> [Id]
    forall a. a -> [a] -> [a]
    : [Id]
    bs'
                      Maybe Id
    Nothing -> [Id]
    bs'
                  , dx
                  , spec_arg : spec_args
                  )
           }

    -- If we run out of binders, stop immediately
    -- See Note [Specialisation Must Preserve Sharing]
    specHeader SpecEnv
    env [] [SpecArg]
    _ = (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    forall a. a -> UniqSM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Bool
    False, SpecEnv
    env, [], [], [], [], [], [])

    -- Return all remaining binders from the original function. These have the
    -- invariant that they should all correspond to unspecialised arguments, so
    -- it's safe to stop processing at this point.
    specHeader SpecEnv
    env [Id]
    bndrs []
      = (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    -> SpecM
         (Bool, SpecEnv, [Id], [Id], [OutExpr], [Id], [DictBind], [OutExpr])
    forall a. a -> UniqSM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Bool
    False, SpecEnv
    env', [Id]
    bndrs', [], [], [], [], [])
      where
        (SpecEnv
    env', [Id]
    bndrs') = SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bndrs

    -- | Binds a dictionary argument to a fresh name, to preserve sharing
    bindAuxiliaryDict
      :: SpecEnv
      -> InId -> OutId -> OutExpr -- Original dict binder, and the witnessing expression
      -> ( SpecEnv        -- Substitutes for orig_dict_id
         , Maybe DictBind -- Auxiliary dict binding, if any
         , OutExpr)       -- Witnessing expression (always trivial)
    bindAuxiliaryDict :: SpecEnv
    -> Id -> Id -> OutExpr -> (SpecEnv, Maybe DictBind, OutExpr)
    bindAuxiliaryDict env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst })
                      Id
    orig_dict_id Id
    fresh_dict_id OutExpr
    dict_expr

      -- If the dictionary argument is trivial,
      -- don’t bother creating a new dict binding; just substitute
      | OutExpr -> Bool
    exprIsTrivial OutExpr
    dict_expr
      = let env' :: SpecEnv
    env' = SpecEnv
    env { se_subst = Core.extendSubst subst orig_dict_id dict_expr }
        in -- pprTrace "bindAuxiliaryDict:trivial" (ppr orig_dict_id <+> ppr dict_id) $
           (SpecEnv
    env', Maybe DictBind
    forall a. Maybe a
    Nothing, OutExpr
    dict_expr)

      | Bool
    otherwise  -- Non-trivial dictionary arg; make an auxiliary binding
      = let fresh_dict_id' :: Id
    fresh_dict_id' = Id
    fresh_dict_id Id -> OutExpr -> Id
    `addDictUnfolding` OutExpr
    dict_expr

            dict_bind :: DictBind
    dict_bind = InBind -> DictBind
    mkDB (Id -> OutExpr -> InBind
    forall b. b -> Expr b -> Bind b
    NonRec Id
    fresh_dict_id' OutExpr
    dict_expr)
            env' :: SpecEnv
    env' = SpecEnv
    env { se_subst = Core.extendSubst subst orig_dict_id (Var fresh_dict_id')
                                    `Core.extendSubstInScope` fresh_dict_id' }
                                    -- Ensure the new unfolding is in the in-scope set
        in -- pprTrace "bindAuxiliaryDict:non-trivial" (ppr orig_dict_id <+> ppr fresh_dict_id') $
           (SpecEnv
    env', DictBind -> Maybe DictBind
    forall a. a -> Maybe a
    Just DictBind
    dict_bind, Id -> OutExpr
    forall b. Id -> Expr b
    Var Id
    fresh_dict_id')

    addDictUnfolding :: Id -> CoreExpr -> Id
    -- Add unfolding for freshly-bound Ids: see Note [Make the new dictionaries interesting]
    -- and Note [Specialisation modulo dictionary selectors]
    addDictUnfolding :: Id -> OutExpr -> Id
    addDictUnfolding Id
    id OutExpr
    rhs
      = Id
    id Id -> Unfolding -> Id
    `setIdUnfolding` UnfoldingOpts -> OutExpr -> Unfolding
    mkSimpleUnfolding UnfoldingOpts
    defaultUnfoldingOpts OutExpr
    rhs

    {-
    Note [Make the new dictionaries interesting]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Important!  We're going to substitute dx_id1 for d
    and we want it to look "interesting", else we won't gather *any*
    consequential calls. E.g.
        f d = ...g d....
    If we specialise f for a call (f (dfun dNumInt)), we'll get
    a consequent call (g d') with an auxiliary definition
        d' = df dNumInt
    We want that consequent call to look interesting; so we add an unfolding
    in the dictionary Id.
    -}

    {- *********************************************************************
    *                                                                      *
                UsageDetails and suchlike
    *                                                                      *
    ********************************************************************* -}

    data UsageDetails
      = MkUD { UsageDetails -> FloatedDictBinds
    ud_binds :: !FloatedDictBinds
             , UsageDetails -> CallDetails
    ud_calls :: !CallDetails }
        -- INVARIANT: suppose bs = fdb_bndrs ud_binds
        -- Then 'calls' may *mention* 'bs',
        -- but there should be no calls *for* bs

    data FloatedDictBinds  -- See Note [Floated dictionary bindings]
      = FDB { FloatedDictBinds -> OrdList DictBind
    fdb_binds :: !(OrdList DictBind)
                   -- The order is important;
                   -- in ds1 `appOL` ds2, bindings in ds2 can depend on those in ds1

            , FloatedDictBinds -> VarSet
    fdb_bndrs :: !IdSet
        }          -- ^ The binders of 'fdb_binds'.
                   -- Caches a superset of the expression
                   --   `mkVarSet (bindersOfDictBinds fdb_binds))`
                   -- for later addition to an InScopeSet

    -- | A 'DictBind' is a binding along with a cached set containing its free
    -- variables (both type variables and dictionaries). We need this set
    -- in splitDictBinds, when filtering bindings to decide which are
    -- captured by a binder
    data DictBind = DB { DictBind -> InBind
    db_bind :: CoreBind, DictBind -> VarSet
    db_fvs :: VarSet }

    bindersOfDictBind :: DictBind -> [Id]
    bindersOfDictBind :: DictBind -> [Id]
    bindersOfDictBind = InBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf (InBind -> [Id]) -> (DictBind -> InBind) -> DictBind -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictBind -> InBind
    db_bind

    bindersOfDictBinds :: Foldable f => f DictBind -> [Id]
    bindersOfDictBinds :: forall (f :: * -> *). Foldable f => f DictBind -> [Id]
    bindersOfDictBinds = CoreProgram -> [Id]
    forall b. [Bind b] -> [b]
    bindersOfBinds (CoreProgram -> [Id])
    -> (f DictBind -> CoreProgram) -> f DictBind -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (DictBind -> CoreProgram -> CoreProgram)
    -> CoreProgram -> f DictBind -> CoreProgram
    forall a b. (a -> b -> b) -> b -> f a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr ((:) (InBind -> CoreProgram -> CoreProgram)
    -> (DictBind -> InBind) -> DictBind -> CoreProgram -> CoreProgram
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictBind -> InBind
    db_bind) []

    {- Note [Floated dictionary bindings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We float out dictionary bindings for the reasons described under
    "Dictionary floating" above.  But not /just/ dictionary bindings.
    Consider

       f :: Eq a => blah
       f a d = rhs

       $c== :: T -> T -> Bool
       $c== x y = ...

       $df :: Eq T
       $df = Eq $c== ...

       gurgle = ...(f @T $df)...

    We gather the call info for (f @T $df), and we don't want to drop it
    when we come across the binding for $df.  So we add $df to the floats
    and continue.  But then we have to add $c== to the floats, and so on.
    These all float above the binding for 'f', and now we can
    successfully specialise 'f'.

    So the DictBinds in (ud_binds :: OrdList DictBind) may contain
    non-dictionary bindings too.

    Note [Specialising polymorphic dictionaries]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Note June 2023: This has proved to be quite a tricky optimisation to get right
    see (#23469, #23109, #21229, #23445) so it is now guarded by a flag
    `-fpolymorphic-specialisation`.

    Consider
        class M a where { foo :: a -> Int }

        instance M (ST s) where ...
        -- dMST :: forall s. M (ST s)

        wimwam :: forall a. M a => a -> Int
        wimwam = /\a \(d::M a). body

        f :: ST s -> Int
        f = /\s \(x::ST s). wimwam @(ST s) (dMST @s) dx + 1

    We'd like to specialise wimwam at (ST s), thus
        $swimwam :: forall s. ST s -> Int
        $swimwam = /\s. body[ST s/a, (dMST @s)/d]

        RULE forall s (d :: M (ST s)).
             wimwam @(ST s) d = $swimwam @s

    Here are the moving parts:

    (MP1) We must /not/ dump the CallInfo
            CIS wimwam (CI { ci_key = [@(ST s), dMST @s]
                           , ci_fvs = {dMST} })
          when we come to the /\s.  Instead, we simply let it continue to float
          upwards. Hence ci_fvs is an IdSet, listing the /Ids/ that
          are free in the call, but not the /TyVars/.  Hence using specArgFreeIds
          in singleCall.

      NB to be fully kosher we should explicitly quantifying the CallInfo
      over 's', but we don't bother.  This would matter if there was an
      enclosing binding of the same 's', which I don't expect to happen.

    (MP2) When we come to specialise the call, we must remember to quantify
          over 's'.  That is done in the SpecType case of specHeader, where
          we add 's' (called qvars) to the binders of the RULE and the specialised
          function.

    (MP3) If we have f :: forall m. Monoid m => blah, and two calls
            (f @(Endo b)      (d :: Monoid (Endo b))
            (f @(Endo (c->c)) (d :: Monoid (Endo (c->c)))
          we want to generate a specialisation only for the first.  The second
          is just a substitution instance of the first, with no greater specialisation.
          Hence the call to `remove_dups` in `filterCalls`.

    All this arose in #13873, in the unexpected form that a SPECIALISE
    pragma made the program slower!  The reason was that the specialised
    function $sinsertWith arising from the pragma looked rather like `f`
    above, and failed to specialise a call in its body like wimwam.
    Without the pragma, the original call to `insertWith` was completely
    monomorpic, and specialised in one go.

    Wrinkles.

    * See Note [Weird special case for SpecDict]

    * With -XOverlappingInstances you might worry about this:
        class C a where ...
        instance C (Maybe Int) where ...   -- $df1 :: C (Maybe Int)
        instance C (Maybe a)   where ...   -- $df2 :: forall a. C (Maybe a)

        f :: C a => blah
        f = rhs

        g = /\a.  ...(f @(Maybe a) ($df2 a))...
        h = ...f @(Maybe Int) $df1

      There are two calls to f, but with different evidence.  This patch will
      combine them into one.  But it's OK: this code will never arise unless you
      use -XIncoherentInstances.  Even with -XOverlappingInstances, GHC tries hard
      to keep dictionaries as singleton types.  But that goes out of the window
      with -XIncoherentInstances -- and that is true even with ordianry type-class
      specialisation (at least if any inlining has taken place).

      GHC makes very few guarantees when you use -XIncoherentInstances, and its
      not worth crippling the normal case for the incoherent corner.  (The best
      thing might be to switch off specialisation altogether if incoherence is
      involved... but incoherence is a property of an instance, not a class, so
      it's a hard test to make.)

      But see Note [Specialisation and overlapping instances].

    Note [Weird special case for SpecDict]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we are trying to specialise for this this call:
       $wsplit @T (mkD @k @(a::k) :: C T)
    where
       mkD :: forall k (a::k). C T
    is a top-level dictionary-former.  This actually happened in #22459,
    because of (MP1) of Note [Specialising polymorphic dictionaries].

    How can we specialise $wsplit?  We might try

       RULE "SPEC" forall (d :: C T). $wsplit @T d = $s$wsplit

    but then in the body of $s$wsplit what will we use for the dictionary
    evidence?  We can't use (mkD @k @(a::k)) because k and a aren't in scope.
    We could zap `k` to (Any @Type) and `a` to (Any @(Any @Type)), but that
    is a lot of hard work for a very strange case.

    So we simply refrain from specialising in this case; hence the guard
       allVarSet (`elemInScopeSet` in_scope) (exprFreeVars d)
    in the SpecDict cased of specHeader.

    How did this strange polymorphic mkD arise in the first place?
    From GHC.Core.Opt.Utils.abstractFloats, which was abstracting
    over too many type variables. But that too is now fixed;
    see Note [Which type variables to abstract over] in that module.
    -}

    instance Outputable DictBind where
      ppr :: DictBind -> SDoc
    ppr (DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs })
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "DB" 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
    "fvs: " SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> VarSet -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr VarSet
    fvs
                                    , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "bind:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> InBind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr InBind
    bind ])

    instance Outputable UsageDetails where
      ppr :: UsageDetails -> SDoc
    ppr (MkUD { ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls })
            = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "MkUD" 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 (SDoc -> [SDoc] -> [SDoc]
    forall doc. IsLine doc => doc -> [doc] -> [doc]
    punctuate SDoc
    forall doc. IsLine doc => doc
    comma
                    [String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "binds" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc
    forall doc. IsLine doc => doc
    equals SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> FloatedDictBinds -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr FloatedDictBinds
    dbs,
                     String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "calls" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> SDoc
    forall doc. IsLine doc => doc
    equals SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> CallDetails -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr CallDetails
    calls]))

    instance Outputable FloatedDictBinds where
      ppr :: FloatedDictBinds -> SDoc
    ppr (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    binds }) = OrdList DictBind -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OrdList DictBind
    binds

    emptyUDs :: UsageDetails
    emptyUDs :: UsageDetails
    emptyUDs = MkUD { ud_binds :: FloatedDictBinds
    ud_binds = FloatedDictBinds
    emptyFDBs, ud_calls :: CallDetails
    ud_calls = CallDetails
    forall a. DVarEnv a
    emptyDVarEnv }

    emptyFDBs :: FloatedDictBinds
    emptyFDBs :: FloatedDictBinds
    emptyFDBs = FDB { fdb_binds :: OrdList DictBind
    fdb_binds = OrdList DictBind
    forall a. OrdList a
    nilOL, fdb_bndrs :: VarSet
    fdb_bndrs = VarSet
    emptyVarSet }

    ------------------------------------------------------------
    type CallDetails  = DIdEnv CallInfoSet
      -- The order of specialized binds and rules depends on how we linearize
      -- CallDetails, so to get determinism we must use a deterministic set here.
      -- See Note [Deterministic UniqFM] in GHC.Types.Unique.DFM

    data CallInfoSet = CIS Id (Bag CallInfo)
      -- The list of types and dictionaries is guaranteed to
      -- match the type of f
      -- The Bag may contain duplicate calls (i.e. f @T and another f @T)
      -- These dups are eliminated by already_covered in specCalls

    data CallInfo
      = CI { CallInfo -> [SpecArg]
    ci_key  :: [SpecArg]   -- All arguments
           , CallInfo -> VarSet
    ci_fvs  :: IdSet       -- Free Ids of the ci_key call
                                    -- /not/ including the main id itself, of course
                                    -- NB: excluding tyvars:
                                    --     See Note [Specialising polymorphic dictionaries]
        }

    type DictExpr = CoreExpr

    ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter CallInfo -> Bool
    p (CIS Id
    id Bag CallInfo
    a) = Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    id ((CallInfo -> Bool) -> Bag CallInfo -> Bag CallInfo
    forall a. (a -> Bool) -> Bag a -> Bag a
    filterBag CallInfo -> Bool
    p Bag CallInfo
    a)

    instance Outputable CallInfoSet where
      ppr :: CallInfoSet -> SDoc
    ppr (CIS Id
    fn Bag CallInfo
    map) = SDoc -> Int -> SDoc -> SDoc
    hang (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "CIS" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn)
                            Int
    2 (Bag CallInfo -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Bag CallInfo
    map)

    pprCallInfo :: Id -> CallInfo -> SDoc
    pprCallInfo :: Id -> CallInfo -> SDoc
    pprCallInfo Id
    fn (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    key })
      = Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    fn SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    key

    instance Outputable CallInfo where
      ppr :: CallInfo -> SDoc
    ppr (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    key, ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    _fvs })
        = String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "CI" 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 ((SpecArg -> SDoc) -> [SpecArg] -> [SDoc]
    forall a b. (a -> b) -> [a] -> [b]
    map SpecArg -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    key))

    unionCalls :: CallDetails -> CallDetails -> CallDetails
    unionCalls :: CallDetails -> CallDetails -> CallDetails
    unionCalls CallDetails
    c1 CallDetails
    c2 = (CallInfoSet -> CallInfoSet -> CallInfoSet)
    -> CallDetails -> CallDetails -> CallDetails
    forall a. (a -> a -> a) -> DVarEnv a -> DVarEnv a -> DVarEnv a
    plusDVarEnv_C CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet CallDetails
    c1 CallDetails
    c2

    unionCallInfoSet :: CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet :: CallInfoSet -> CallInfoSet -> CallInfoSet
    unionCallInfoSet (CIS Id
    f Bag CallInfo
    calls1) (CIS Id
    _ Bag CallInfo
    calls2) =
      Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    f (Bag CallInfo
    calls1 Bag CallInfo -> Bag CallInfo -> Bag CallInfo
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` Bag CallInfo
    calls2)

    callDetailsFVs :: CallDetails -> VarSet
    callDetailsFVs :: CallDetails -> VarSet
    callDetailsFVs CallDetails
    calls =
      (CallInfoSet -> VarSet -> VarSet)
    -> VarSet -> CallDetails -> VarSet
    forall {k} elt a (key :: k).
    (elt -> a -> a) -> a -> UniqDFM key elt -> a
    nonDetStrictFoldUDFM (VarSet -> VarSet -> VarSet
    unionVarSet (VarSet -> VarSet -> VarSet)
    -> (CallInfoSet -> VarSet) -> CallInfoSet -> VarSet -> VarSet
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . CallInfoSet -> VarSet
    callInfoFVs) VarSet
    emptyVarSet CallDetails
    calls
      -- It's OK to use nonDetStrictFoldUDFM here because we forget the ordering
      -- immediately by converting to a nondeterministic set.

    callInfoFVs :: CallInfoSet -> VarSet
    callInfoFVs :: CallInfoSet -> VarSet
    callInfoFVs (CIS Id
    _ Bag CallInfo
    call_info) =
      (CallInfo -> VarSet -> VarSet) -> VarSet -> Bag CallInfo -> VarSet
    forall a b. (a -> b -> b) -> b -> Bag a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (\(CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fv }) VarSet
    vs -> VarSet -> VarSet -> VarSet
    unionVarSet VarSet
    fv VarSet
    vs) VarSet
    emptyVarSet Bag CallInfo
    call_info

    getTheta :: [PiTyBinder] -> [PredType]
    getTheta :: [PiTyBinder] -> [Kind]
    getTheta = (PiTyBinder -> Kind) -> [PiTyBinder] -> [Kind]
    forall a b. (a -> b) -> [a] -> [b]
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap PiTyBinder -> Kind
    piTyBinderType ([PiTyBinder] -> [Kind])
    -> ([PiTyBinder] -> [PiTyBinder]) -> [PiTyBinder] -> [Kind]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (PiTyBinder -> Bool) -> [PiTyBinder] -> [PiTyBinder]
    forall a. (a -> Bool) -> [a] -> [a]
    filter PiTyBinder -> Bool
    isInvisiblePiTyBinder ([PiTyBinder] -> [PiTyBinder])
    -> ([PiTyBinder] -> [PiTyBinder]) -> [PiTyBinder] -> [PiTyBinder]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (PiTyBinder -> Bool) -> [PiTyBinder] -> [PiTyBinder]
    forall a. (a -> Bool) -> [a] -> [a]
    filter PiTyBinder -> Bool
    isAnonPiTyBinder

    ------------------------------------------------------------
    singleCall :: SpecEnv -> Id -> [SpecArg] -> UsageDetails
    singleCall :: SpecEnv -> Id -> [SpecArg] -> UsageDetails
    singleCall SpecEnv
    spec_env Id
    id [SpecArg]
    args
      = MkUD {ud_binds :: FloatedDictBinds
    ud_binds = FloatedDictBinds
    emptyFDBs,
              ud_calls :: CallDetails
    ud_calls = Id -> CallInfoSet -> CallDetails
    forall a. Id -> a -> DVarEnv a
    unitDVarEnv Id
    id (CallInfoSet -> CallDetails) -> CallInfoSet -> CallDetails
    forall a b. (a -> b) -> a -> b
    $ Id -> Bag CallInfo -> CallInfoSet
    CIS Id
    id (Bag CallInfo -> CallInfoSet) -> Bag CallInfo -> CallInfoSet
    forall a b. (a -> b) -> a -> b
    $
                         CallInfo -> Bag CallInfo
    forall a. a -> Bag a
    unitBag (CI { ci_key :: [SpecArg]
    ci_key  = [SpecArg]
    args
                                     , ci_fvs :: VarSet
    ci_fvs  = VarSet
    call_fvs }) }
      where
        call_fvs :: VarSet
    call_fvs =
          (SpecArg -> VarSet -> VarSet) -> VarSet -> [SpecArg] -> VarSet
    forall a b. (a -> b -> b) -> b -> [a] -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr (VarSet -> VarSet -> VarSet
    unionVarSet (VarSet -> VarSet -> VarSet)
    -> (SpecArg -> VarSet) -> SpecArg -> VarSet -> VarSet
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . SpecArg -> VarSet
    free_var_fn) VarSet
    emptyVarSet [SpecArg]
    args

        free_var_fn :: SpecArg -> VarSet
    free_var_fn =
          if GeneralFlag -> DynFlags -> Bool
    gopt GeneralFlag
    Opt_PolymorphicSpecialisation (SpecEnv -> DynFlags
    se_dflags SpecEnv
    spec_env)
            then SpecArg -> VarSet
    specArgFreeIds
            else SpecArg -> VarSet
    specArgFreeVars

            -- specArgFreeIds: we specifically look for free Ids, not TyVars
            --    see (MP1) in Note [Specialising polymorphic dictionaries]
            --
            -- We don't include the 'id' itself.

    mkCallUDs :: SpecEnv -> OutExpr -> [OutExpr] -> UsageDetails
    mkCallUDs :: SpecEnv -> OutExpr -> [OutExpr] -> UsageDetails
    mkCallUDs SpecEnv
    env OutExpr
    fun [OutExpr]
    args
      | ([CoreTickish]
    _, Var Id
    f) <- (CoreTickish -> Bool) -> OutExpr -> ([CoreTickish], OutExpr)
    forall b.
    (CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b)
    stripTicksTop CoreTickish -> Bool
    forall (pass :: TickishPass). GenTickish pass -> Bool
    tickishFloatable OutExpr
    fun -- See Note [Ticks on applications]
      = -- pprTraceWith "mkCallUDs" (\res -> vcat [ ppr f, ppr args, ppr res ]) $
        SpecEnv -> Id -> [OutExpr] -> UsageDetails
    mkCallUDs' SpecEnv
    env Id
    f [OutExpr]
    args
      | Bool
    otherwise
      = UsageDetails
    emptyUDs

    mkCallUDs' :: SpecEnv -> Id -> [OutExpr] -> UsageDetails
    mkCallUDs' :: SpecEnv -> Id -> [OutExpr] -> UsageDetails
    mkCallUDs' SpecEnv
    env Id
    f [OutExpr]
    args
      | SpecEnv -> Id -> Bool
    wantCallsFor SpecEnv
    env Id
    f    -- We want it, and...
      , Bool -> Bool
    not ([SpecArg] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [SpecArg]
    ci_key)     -- this call site has a useful specialisation
      = -- pprTrace "mkCallUDs: keeping" _trace_doc
        SpecEnv -> Id -> [SpecArg] -> UsageDetails
    singleCall SpecEnv
    env Id
    f [SpecArg]
    ci_key

      | Bool
    otherwise  -- See also Note [Specialisations already covered]
      = -- pprTrace "mkCallUDs: discarding" _trace_doc
        UsageDetails
    emptyUDs

      where
        _trace_doc :: SDoc
    _trace_doc = [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [Id -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Id
    f, [OutExpr] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [OutExpr]
    args, [SpecArg] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [SpecArg]
    ci_key]
        pis :: [PiTyBinder]
    pis                = ([PiTyBinder], Kind) -> [PiTyBinder]
    forall a b. (a, b) -> a
    fst (([PiTyBinder], Kind) -> [PiTyBinder])
    -> ([PiTyBinder], Kind) -> [PiTyBinder]
    forall a b. (a -> b) -> a -> b
    $ Kind -> ([PiTyBinder], Kind)
    splitPiTys (Kind -> ([PiTyBinder], Kind)) -> Kind -> ([PiTyBinder], Kind)
    forall a b. (a -> b) -> a -> b
    $ Id -> Kind
    idType Id
    f
        constrained_tyvars :: VarSet
    constrained_tyvars = [Kind] -> VarSet
    tyCoVarsOfTypes ([Kind] -> VarSet) -> [Kind] -> VarSet
    forall a b. (a -> b) -> a -> b
    $ [PiTyBinder] -> [Kind]
    getTheta [PiTyBinder]
    pis

        ci_key :: [SpecArg]
        ci_key :: [SpecArg]
    ci_key = (SpecArg -> Bool) -> [SpecArg] -> [SpecArg]
    forall a. (a -> Bool) -> [a] -> [a]
    dropWhileEndLE (Bool -> Bool
    not (Bool -> Bool) -> (SpecArg -> Bool) -> SpecArg -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . SpecArg -> Bool
    isSpecDict) ([SpecArg] -> [SpecArg]) -> [SpecArg] -> [SpecArg]
    forall a b. (a -> b) -> a -> b
    $
                 (OutExpr -> PiTyBinder -> SpecArg)
    -> [OutExpr] -> [PiTyBinder] -> [SpecArg]
    forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
    zipWith OutExpr -> PiTyBinder -> SpecArg
    mk_spec_arg [OutExpr]
    args [PiTyBinder]
    pis
                 -- Drop trailing args until we get to a SpecDict
                 -- In this way the RULE has as few args as possible,
                 -- which broadens its applicability, since rules only
                 -- fire when saturated

        mk_spec_arg :: OutExpr -> PiTyBinder -> SpecArg
        mk_spec_arg :: OutExpr -> PiTyBinder -> SpecArg
    mk_spec_arg OutExpr
    arg (Named ForAllTyBinder
    bndr)
          |  ForAllTyBinder -> Id
    forall tv argf. VarBndr tv argf -> tv
    binderVar ForAllTyBinder
    bndr Id -> VarSet -> Bool
    `elemVarSet` VarSet
    constrained_tyvars
          = case OutExpr
    arg of
              Type Kind
    ty -> Kind -> SpecArg
    SpecType Kind
    ty
              OutExpr
    _       -> String -> SDoc -> SpecArg
    forall a. HasCallStack => String -> SDoc -> a
    pprPanic String
    "ci_key" (SDoc -> SpecArg) -> SDoc -> SpecArg
    forall a b. (a -> b) -> a -> b
    $ OutExpr -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr OutExpr
    arg
          |  Bool
    otherwise = SpecArg
    UnspecType

        -- For "invisibleFunArg", which are the type-class dictionaries,
        -- we decide on a case by case basis if we want to specialise
        -- on this argument; if so, SpecDict, if not UnspecArg
        mk_spec_arg OutExpr
    arg (Anon Scaled Kind
    pred FunTyFlag
    af)
          | FunTyFlag -> Bool
    isInvisibleFunArg FunTyFlag
    af
          , OutExpr -> Kind -> Bool
    interestingDict OutExpr
    arg (Scaled Kind -> Kind
    forall a. Scaled a -> a
    scaledThing Scaled Kind
    pred)
                  -- See Note [Interesting dictionary arguments]
          = OutExpr -> SpecArg
    SpecDict OutExpr
    arg

          | Bool
    otherwise = SpecArg
    UnspecArg

    {-
    Note [Ticks on applications]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Ticks such as source location annotations can sometimes make their way
    onto applications (see e.g. #21697). So if we see something like

        App (Tick _ f) e

    we need to descend below the tick to find what the real function being
    applied is.

    The resulting RULE also has to be able to match this annotated use
    site, so we only look through ticks that RULE matching looks through
    (see Note [Tick annotations in RULE matching] in GHC.Core.Rules).
    -}

    wantCallsFor :: SpecEnv -> Id -> Bool
    wantCallsFor :: SpecEnv -> Id -> Bool
    wantCallsFor SpecEnv
    _env Id
    _f = Bool
    True
     -- We could reduce the size of the UsageDetails by being less eager
     -- about collecting calls for LocalIds: there is no point for
     -- ones that are lambda-bound.  We can't decide this by looking at
     -- the (absence of an) unfolding, because unfoldings for local
     -- functions are discarded by cloneBindSM, so no local binder will
     -- have an unfolding at this stage.  We'd have to keep a candidate
     -- set of let-binders.
     --
     -- Not many lambda-bound variables have dictionary arguments, so
     -- this would make little difference anyway.
     --
     -- For imported Ids we could check for an unfolding, but we have to
     -- do so anyway in canSpecImport, and it seems better to have it
     -- all in one place.  So we simply collect usage info for imported
     -- overloaded functions.

    {- Note [Interesting dictionary arguments]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this
             \a.\d:Eq a.  let f = ... in ...(f d)...
    There really is not much point in specialising f wrt the dictionary d,
    because the code for the specialised f is not improved at all, because
    d is lambda-bound.  We simply get junk specialisations.

    What is "interesting"?  Just that it has *some* structure.  But what about
    variables?  We look in the variable's /unfolding/.  And that means
    that we must be careful to ensure that dictionaries have unfoldings,

    * cloneBndrSM discards non-Stable unfoldings
    * specBind updates the unfolding after specialisation
      See Note [Update unfolding after specialisation]
    * bindAuxiliaryDict adds an unfolding for an aux dict
      see Note [Specialisation modulo dictionary selectors]
    * specCase adds unfoldings for the new bindings it creates

    We accidentally lost accurate tracking of local variables for a long
    time, because cloned variables didn't have unfoldings. But makes a
    massive difference in a few cases, eg #5113. For nofib as a
    whole it's only a small win: 2.2% improvement in allocation for ansi,
    1.2% for bspt, but mostly 0.0!  Average 0.1% increase in binary size.

    Note [Update unfolding after specialisation]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider (#21848)

      wombat :: Show b => Int -> b -> String
      wombat a b | a>0       = wombat (a-1) b
                 | otherwise = show a ++ wombat a b

      class C a where
        meth :: Show b => a -> b -> String
        dummy :: a -> () -- Force a datatype dictionary representation

      instance C Int where
        meth = wombat
        dummy _ = ()

      class C a => D a   -- D has C as a superclass
      instance D Int

      f :: (D a, Show b) => a -> b -> String
      {-# INLINABLE[0] f #-}
      f a b = meth a b ++ "!" ++ meth a b

    Now `f` turns into:

      f @a @b (dd :: D a) (ds :: Show b) a b
         = let dc :: D a = %p1 dd  -- Superclass selection
           in meth @a dc ....
              meth @a dc ....

    When we specialise `f`, at a=Int say, that superclass selection can
    nfire (via rewiteClassOps), but that info (that 'dc' is now a
    particular dictionary `C`, of type `C Int`) must be available to
    the call `meth @a dc`, so that we can fire the `meth` class-op, and
    thence specialise `wombat`.

    We deliver on this idea by updating the unfolding for the binder
    in the NonRec case of specBind.  (This is too exotic to trouble with
    the Rec case.)
    -}

    interestingDict :: CoreExpr -> Type -> Bool
    -- A dictionary argument is interesting if it has *some* structure,
    -- see Note [Interesting dictionary arguments]
    -- NB: "dictionary" arguments include constraints of all sorts,
    --     including equality constraints; hence the Coercion case
    -- To make this work, we need to ensure that dictionaries have
    -- unfoldings in them.
    interestingDict :: OutExpr -> Kind -> Bool
    interestingDict OutExpr
    arg Kind
    arg_ty
      | Bool -> Bool
    not (Kind -> Bool
    typeDeterminesValue Kind
    arg_ty) = Bool
    False   -- See Note [Type determines value]
      | Bool
    otherwise                        = OutExpr -> Bool
    forall b. Expr b -> Bool
    go OutExpr
    arg
      where
        go :: Expr b -> Bool
    go (Var Id
    v)               =  Unfolding -> Bool
    hasSomeUnfolding (Id -> Unfolding
    idUnfolding Id
    v)
                                 Bool -> Bool -> Bool
    || Id -> Bool
    isDataConWorkId Id
    v
        go (Type Kind
    _)              = Bool
    False
        go (Coercion Coercion
    _)          = Bool
    False
        go (App Expr b
    fn (Type Kind
    _))     = Expr b -> Bool
    go Expr b
    fn
        go (App Expr b
    fn (Coercion Coercion
    _)) = Expr b -> Bool
    go Expr b
    fn
        go (Tick CoreTickish
    _ Expr b
    a)            = Expr b -> Bool
    go Expr b
    a
        go (Cast Expr b
    e Coercion
    _)            = Expr b -> Bool
    go Expr b
    e
        go Expr b
    _                     = Bool
    True

    thenUDs :: UsageDetails -> UsageDetails -> UsageDetails
    thenUDs :: UsageDetails -> UsageDetails -> UsageDetails
    thenUDs (MkUD {ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    db1, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls1})
            (MkUD {ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    db2, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    calls2})
      = MkUD { ud_binds :: FloatedDictBinds
    ud_binds       = FloatedDictBinds
    db1    FloatedDictBinds -> FloatedDictBinds -> FloatedDictBinds
    `thenFDBs`   FloatedDictBinds
    db2
             , ud_calls :: CallDetails
    ud_calls       = CallDetails
    calls1 CallDetails -> CallDetails -> CallDetails
    `unionCalls`  CallDetails
    calls2 }

    thenFDBs :: FloatedDictBinds -> FloatedDictBinds -> FloatedDictBinds
    -- Combine FloatedDictBinds
    -- In (dbs1 `thenFDBs` dbs2), dbs2 may mention dbs1 but not vice versa
    thenFDBs :: FloatedDictBinds -> FloatedDictBinds -> FloatedDictBinds
    thenFDBs (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs1, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs1 })
             (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs2, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs2 })
      = FDB { fdb_binds :: OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs1 OrdList DictBind -> OrdList DictBind -> OrdList DictBind
    forall a. OrdList a -> OrdList a -> OrdList a
    `appOL` OrdList DictBind
    dbs2
            , fdb_bndrs :: VarSet
    fdb_bndrs = VarSet
    bs1  VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    bs2 }

    -----------------------------
    _dictBindBndrs :: OrdList DictBind -> [Id]
    _dictBindBndrs :: OrdList DictBind -> [Id]
    _dictBindBndrs OrdList DictBind
    dbs = (DictBind -> [Id] -> [Id]) -> [Id] -> OrdList DictBind -> [Id]
    forall a b. (a -> b -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr ([Id] -> [Id] -> [Id]
    forall a. [a] -> [a] -> [a]
    (++) ([Id] -> [Id] -> [Id])
    -> (DictBind -> [Id]) -> DictBind -> [Id] -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . InBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf (InBind -> [Id]) -> (DictBind -> InBind) -> DictBind -> [Id]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . DictBind -> InBind
    db_bind) [] OrdList DictBind
    dbs

    -- | Construct a 'DictBind' from a 'CoreBind'
    mkDB :: CoreBind -> DictBind
    mkDB :: InBind -> DictBind
    mkDB InBind
    bind = DB { db_bind :: InBind
    db_bind = InBind
    bind, db_fvs :: VarSet
    db_fvs = InBind -> VarSet
    bind_fvs InBind
    bind }

    -- | Identify the free variables of a 'CoreBind'
    bind_fvs :: CoreBind -> VarSet
    bind_fvs :: InBind -> VarSet
    bind_fvs (NonRec Id
    bndr OutExpr
    rhs) = (Id, OutExpr) -> VarSet
    pair_fvs (Id
    bndr,OutExpr
    rhs)
    bind_fvs (Rec [(Id, OutExpr)]
    prs)         = VarSet
    rhs_fvs VarSet -> [Id] -> VarSet
    `delVarSetList` (((Id, OutExpr) -> Id) -> [(Id, OutExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, OutExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, OutExpr)]
    prs)
                               where
                                 rhs_fvs :: VarSet
    rhs_fvs = [VarSet] -> VarSet
    unionVarSets (((Id, OutExpr) -> VarSet) -> [(Id, OutExpr)] -> [VarSet]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, OutExpr) -> VarSet
    pair_fvs [(Id, OutExpr)]
    prs)

    pair_fvs :: (Id, CoreExpr) -> VarSet
    pair_fvs :: (Id, OutExpr) -> VarSet
    pair_fvs (Id
    bndr, OutExpr
    rhs) = (Id -> Bool) -> OutExpr -> VarSet
    exprSomeFreeVars Id -> Bool
    interesting OutExpr
    rhs
                           VarSet -> VarSet -> VarSet
    `unionVarSet` Id -> VarSet
    idFreeVars Id
    bndr
            -- idFreeVars: don't forget variables mentioned in
            -- the rules of the bndr.  C.f. OccAnal.addRuleUsage
            -- Also tyvars mentioned in its type; they may not appear
            -- in the RHS
            --      type T a = Int
            --      x :: T a = 3
      where
        interesting :: InterestingVarFun
        interesting :: Id -> Bool
    interesting Id
    v = Id -> Bool
    isLocalVar Id
    v Bool -> Bool -> Bool
    || (Id -> Bool
    isId Id
    v Bool -> Bool -> Bool
    && Id -> Bool
    isDFunId Id
    v)
            -- Very important: include DFunIds /even/ if it is imported
            -- Reason: See Note [Avoiding loops in specImports], the #13429
            --         example involving an imported dfun.  We must know
            --         whether a dictionary binding depends on an imported
            --         DFun in case we try to specialise that imported DFun

    -- | Flatten a set of "dumped" 'DictBind's, and some other binding
    -- pairs, into a single recursive binding.
    recWithDumpedDicts :: [(Id,CoreExpr)] -> OrdList DictBind -> DictBind
    recWithDumpedDicts :: [(Id, OutExpr)] -> OrdList DictBind -> DictBind
    recWithDumpedDicts [(Id, OutExpr)]
    pairs OrdList DictBind
    dbs
      = DB { db_bind :: InBind
    db_bind = [(Id, OutExpr)] -> InBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, OutExpr)]
    bindings
           , db_fvs :: VarSet
    db_fvs = VarSet
    fvs VarSet -> [Id] -> VarSet
    `delVarSetList` ((Id, OutExpr) -> Id) -> [(Id, OutExpr)] -> [Id]
    forall a b. (a -> b) -> [a] -> [b]
    map (Id, OutExpr) -> Id
    forall a b. (a, b) -> a
    fst [(Id, OutExpr)]
    bindings }
      where
        ([(Id, OutExpr)]
    bindings, VarSet
    fvs) = (DictBind
     -> ([(Id, OutExpr)], VarSet) -> ([(Id, OutExpr)], VarSet))
    -> ([(Id, OutExpr)], VarSet)
    -> OrdList DictBind
    -> ([(Id, OutExpr)], VarSet)
    forall a b. (a -> b -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> ([(Id, OutExpr)], VarSet) -> ([(Id, OutExpr)], VarSet)
    add ([], VarSet
    emptyVarSet)
                                    (OrdList DictBind
    dbs OrdList DictBind -> DictBind -> OrdList DictBind
    forall a. OrdList a -> a -> OrdList a
    `snocOL` InBind -> DictBind
    mkDB ([(Id, OutExpr)] -> InBind
    forall b. [(b, Expr b)] -> Bind b
    Rec [(Id, OutExpr)]
    pairs))
        add :: DictBind -> ([(Id, OutExpr)], VarSet) -> ([(Id, OutExpr)], VarSet)
    add (DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs }) ([(Id, OutExpr)]
    prs_acc, VarSet
    fvs_acc)
          = case InBind
    bind of
              NonRec Id
    b OutExpr
    r -> ((Id
    b,OutExpr
    r) (Id, OutExpr) -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a. a -> [a] -> [a]
    : [(Id, OutExpr)]
    prs_acc, VarSet
    fvs')
              Rec [(Id, OutExpr)]
    prs1   -> ([(Id, OutExpr)]
    prs1 [(Id, OutExpr)] -> [(Id, OutExpr)] -> [(Id, OutExpr)]
    forall a. [a] -> [a] -> [a]
    ++ [(Id, OutExpr)]
    prs_acc, VarSet
    fvs')
          where
            fvs' :: VarSet
    fvs' = VarSet
    fvs_acc VarSet -> VarSet -> VarSet
    `unionVarSet` VarSet
    fvs

    snocDictBind :: UsageDetails -> DictBind -> UsageDetails
    snocDictBind :: UsageDetails -> DictBind -> UsageDetails
    snocDictBind uds :: UsageDetails
    uds@MkUD{ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds= FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs }} DictBind
    db
      = UsageDetails
    uds { ud_binds = FDB { fdb_binds = dbs `snocOL` db
                             , fdb_bndrs = bs `extendVarSetList` bindersOfDictBind db } }

    snocDictBinds :: UsageDetails -> [DictBind] -> UsageDetails
    -- Add ud_binds to the tail end of the bindings in uds
    snocDictBinds :: UsageDetails -> [DictBind] -> UsageDetails
    snocDictBinds uds :: UsageDetails
    uds@MkUD{ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds=FDB{ fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    binds, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs }} [DictBind]
    dbs
      = UsageDetails
    uds { ud_binds = FDB { fdb_binds = binds `appOL`        (toOL dbs)
                             , fdb_bndrs = bs    `extendVarSetList` bindersOfDictBinds dbs } }

    consDictBinds :: [DictBind] -> UsageDetails -> UsageDetails
    consDictBinds :: [DictBind] -> UsageDetails -> UsageDetails
    consDictBinds [DictBind]
    dbs uds :: UsageDetails
    uds@MkUD{ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds=FDB{fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    binds, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs}}
      = UsageDetails
    uds { ud_binds = FDB{ fdb_binds = toOL dbs `appOL` binds
                            , fdb_bndrs = bs `extendVarSetList` bindersOfDictBinds dbs } }

    wrapDictBinds :: FloatedDictBinds -> [CoreBind] -> [CoreBind]
    wrapDictBinds :: FloatedDictBinds -> CoreProgram -> CoreProgram
    wrapDictBinds (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs }) CoreProgram
    binds
      = (DictBind -> CoreProgram -> CoreProgram)
    -> CoreProgram -> OrdList DictBind -> CoreProgram
    forall a b. (a -> b -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> CoreProgram -> CoreProgram
    add CoreProgram
    binds OrdList DictBind
    dbs
      where
        add :: DictBind -> CoreProgram -> CoreProgram
    add (DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind }) CoreProgram
    binds = InBind
    bind InBind -> CoreProgram -> CoreProgram
    forall a. a -> [a] -> [a]
    : CoreProgram
    binds

    wrapDictBindsE :: OrdList DictBind -> CoreExpr -> CoreExpr
    wrapDictBindsE :: OrdList DictBind -> OutExpr -> OutExpr
    wrapDictBindsE OrdList DictBind
    dbs OutExpr
    expr
      = (DictBind -> OutExpr -> OutExpr)
    -> OutExpr -> OrdList DictBind -> OutExpr
    forall a b. (a -> b -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr DictBind -> OutExpr -> OutExpr
    add OutExpr
    expr OrdList DictBind
    dbs
      where
        add :: DictBind -> OutExpr -> OutExpr
    add (DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind }) OutExpr
    expr = InBind -> OutExpr -> OutExpr
    forall b. Bind b -> Expr b -> Expr b
    Let InBind
    bind OutExpr
    expr

    ----------------------
    dumpUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, OrdList DictBind)
    -- Used at a lambda or case binder; just dump anything mentioning the binder
    dumpUDs :: [Id] -> UsageDetails -> (UsageDetails, OrdList DictBind)
    dumpUDs [Id]
    bndrs uds :: UsageDetails
    uds@(MkUD { ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls })
      | [Id] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [Id]
    bndrs = (UsageDetails
    uds, OrdList DictBind
    forall a. OrdList a
    nilOL)  -- Common in case alternatives
      | Bool
    otherwise  = -- pprTrace "dumpUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs) $
                     (UsageDetails
    free_uds, OrdList DictBind
    dump_dbs)
      where
        free_uds :: UsageDetails
    free_uds = UsageDetails
    uds { ud_binds = free_dbs, ud_calls = free_calls }
        bndr_set :: VarSet
    bndr_set = [Id] -> VarSet
    mkVarSet [Id]
    bndrs
        (FloatedDictBinds
    free_dbs, OrdList DictBind
    dump_dbs, VarSet
    dump_set) = FloatedDictBinds
    -> VarSet -> (FloatedDictBinds, OrdList DictBind, VarSet)
    splitDictBinds FloatedDictBinds
    orig_dbs VarSet
    bndr_set
        free_calls :: CallDetails
    free_calls = VarSet -> CallDetails -> CallDetails
    deleteCallsMentioning VarSet
    dump_set (CallDetails -> CallDetails) -> CallDetails -> CallDetails
    forall a b. (a -> b) -> a -> b
    $   -- Drop calls mentioning bndr_set on the floor
                     [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bndrs CallDetails
    orig_calls    -- Discard calls for bndr_set; there should be
                                                        -- no calls for any of the dicts in dump_dbs

    dumpBindUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, OrdList DictBind, Bool)
    -- Used at a let(rec) binding.
    -- We return a boolean indicating whether the binding itself is mentioned,
    -- directly or indirectly, by any of the ud_calls; in that case we want to
    -- float the binding itself;
    -- See Note [Floated dictionary bindings]
    dumpBindUDs :: [Id] -> UsageDetails -> (UsageDetails, OrdList DictBind, Bool)
    dumpBindUDs [Id]
    bndrs (MkUD { ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls })
      = -- pprTrace "dumpBindUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs $$ ppr float_all) $
        (UsageDetails
    free_uds, OrdList DictBind
    dump_dbs, Bool
    float_all)
      where
        free_uds :: UsageDetails
    free_uds = MkUD { ud_binds :: FloatedDictBinds
    ud_binds = FloatedDictBinds
    free_dbs, ud_calls :: CallDetails
    ud_calls = CallDetails
    free_calls }
        bndr_set :: VarSet
    bndr_set = [Id] -> VarSet
    mkVarSet [Id]
    bndrs
        (FloatedDictBinds
    free_dbs, OrdList DictBind
    dump_dbs, VarSet
    dump_set) = FloatedDictBinds
    -> VarSet -> (FloatedDictBinds, OrdList DictBind, VarSet)
    splitDictBinds FloatedDictBinds
    orig_dbs VarSet
    bndr_set
        free_calls :: CallDetails
    free_calls = [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bndrs CallDetails
    orig_calls
        float_all :: Bool
    float_all = VarSet
    dump_set VarSet -> VarSet -> Bool
    `intersectsVarSet` CallDetails -> VarSet
    callDetailsFVs CallDetails
    free_calls

    callsForMe :: Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe :: Id -> UsageDetails -> (UsageDetails, [CallInfo])
    callsForMe Id
    fn uds :: UsageDetails
    uds@MkUD { ud_binds :: UsageDetails -> FloatedDictBinds
    ud_binds = FloatedDictBinds
    orig_dbs, ud_calls :: UsageDetails -> CallDetails
    ud_calls = CallDetails
    orig_calls }
      = -- pprTrace ("callsForMe")
        --          (vcat [ppr fn,
        --                 text "Orig dbs ="     <+> ppr (_dictBindBndrs orig_dbs),
        --                 text "Orig calls ="   <+> ppr orig_calls,
        --                 text "Calls for me =" <+> ppr calls_for_me]) $
        (UsageDetails
    uds_without_me, [CallInfo]
    calls_for_me)
      where
        uds_without_me :: UsageDetails
    uds_without_me = UsageDetails
    uds { ud_calls = delDVarEnv orig_calls fn }
        calls_for_me :: [CallInfo]
    calls_for_me = case CallDetails -> Id -> Maybe CallInfoSet
    forall a. DVarEnv a -> Id -> Maybe a
    lookupDVarEnv CallDetails
    orig_calls Id
    fn of
                            Maybe CallInfoSet
    Nothing -> []
                            Just CallInfoSet
    cis -> CallInfoSet -> FloatedDictBinds -> [CallInfo]
    filterCalls CallInfoSet
    cis FloatedDictBinds
    orig_dbs
             -- filterCalls: drop calls that (directly or indirectly)
             -- refer to fn.  See Note [Avoiding loops (DFuns)]

    ----------------------
    filterCalls :: CallInfoSet -> FloatedDictBinds -> [CallInfo]
    -- Remove dominated calls (Note [Specialising polymorphic dictionaries])
    -- and loopy DFuns (Note [Avoiding loops (DFuns)])
    filterCalls :: CallInfoSet -> FloatedDictBinds -> [CallInfo]
    filterCalls (CIS Id
    fn Bag CallInfo
    call_bag) (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs })
      | Id -> Bool
    isDFunId Id
    fn  -- Note [Avoiding loops (DFuns)] applies only to DFuns
      = (CallInfo -> Bool) -> [CallInfo] -> [CallInfo]
    forall a. (a -> Bool) -> [a] -> [a]
    filter CallInfo -> Bool
    ok_call [CallInfo]
    de_dupd_calls
      | Bool
    otherwise         -- Do not apply it to non-DFuns
      = [CallInfo]
    de_dupd_calls  -- See Note [Avoiding loops (non-DFuns)]
      where
        de_dupd_calls :: [CallInfo]
    de_dupd_calls = Bag CallInfo -> [CallInfo]
    remove_dups Bag CallInfo
    call_bag

        dump_set :: VarSet
    dump_set = (VarSet -> DictBind -> VarSet)
    -> VarSet -> OrdList DictBind -> VarSet
    forall b a. (b -> a -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' VarSet -> DictBind -> VarSet
    go (Id -> VarSet
    unitVarSet Id
    fn) OrdList DictBind
    dbs
          -- This dump-set could also be computed by splitDictBinds
          --   (_,_,dump_set) = splitDictBinds dbs {fn}
          -- But this variant is shorter

        go :: VarSet -> DictBind -> VarSet
    go VarSet
    so_far (DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs })
           | VarSet
    fvs VarSet -> VarSet -> Bool
    `intersectsVarSet` VarSet
    so_far
           = VarSet -> [Id] -> VarSet
    extendVarSetList VarSet
    so_far (InBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf InBind
    bind)
           | Bool
    otherwise = VarSet
    so_far

        ok_call :: CallInfo -> Bool
    ok_call (CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fvs }) = VarSet
    fvs VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    dump_set

    remove_dups :: Bag CallInfo -> [CallInfo]
    -- Calls involving more generic instances beat more specific ones.
    -- See (MP3) in Note [Specialising polymorphic dictionaries]
    remove_dups :: Bag CallInfo -> [CallInfo]
    remove_dups Bag CallInfo
    calls = (CallInfo -> [CallInfo] -> [CallInfo])
    -> [CallInfo] -> Bag CallInfo -> [CallInfo]
    forall a b. (a -> b -> b) -> b -> Bag a -> b
    forall (t :: * -> *) a b.
    Foldable t =>
    (a -> b -> b) -> b -> t a -> b
    foldr CallInfo -> [CallInfo] -> [CallInfo]
    add [] Bag CallInfo
    calls
      where
        add :: CallInfo -> [CallInfo] -> [CallInfo]
        add :: CallInfo -> [CallInfo] -> [CallInfo]
    add CallInfo
    ci [] = [CallInfo
    ci]
        add CallInfo
    ci1 (CallInfo
    ci2:[CallInfo]
    cis) | CallInfo
    ci2 CallInfo -> CallInfo -> Bool
    `beats_or_same` CallInfo
    ci1 = CallInfo
    ci2CallInfo -> [CallInfo] -> [CallInfo]
    forall a. a -> [a] -> [a]
    :[CallInfo]
    cis
                          | CallInfo
    ci1 CallInfo -> CallInfo -> Bool
    `beats_or_same` CallInfo
    ci2 = CallInfo
    ci1CallInfo -> [CallInfo] -> [CallInfo]
    forall a. a -> [a] -> [a]
    :[CallInfo]
    cis
                          | Bool
    otherwise               = CallInfo
    ci2 CallInfo -> [CallInfo] -> [CallInfo]
    forall a. a -> [a] -> [a]
    : CallInfo -> [CallInfo] -> [CallInfo]
    add CallInfo
    ci1 [CallInfo]
    cis

    beats_or_same :: CallInfo -> CallInfo -> Bool
    beats_or_same :: CallInfo -> CallInfo -> Bool
    beats_or_same (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    args1 }) (CI { ci_key :: CallInfo -> [SpecArg]
    ci_key = [SpecArg]
    args2 })
      = [SpecArg] -> [SpecArg] -> Bool
    go [SpecArg]
    args1 [SpecArg]
    args2
      where
        go :: [SpecArg] -> [SpecArg] -> Bool
    go [] [SpecArg]
    _ = Bool
    True
        go (SpecArg
    arg1:[SpecArg]
    args1) (SpecArg
    arg2:[SpecArg]
    args2) = SpecArg -> SpecArg -> Bool
    go_arg SpecArg
    arg1 SpecArg
    arg2 Bool -> Bool -> Bool
    && [SpecArg] -> [SpecArg] -> Bool
    go [SpecArg]
    args1 [SpecArg]
    args2
        go (SpecArg
    _:[SpecArg]
    _)        []           = Bool
    False

        go_arg :: SpecArg -> SpecArg -> Bool
    go_arg (SpecType Kind
    ty1) (SpecType Kind
    ty2) = Maybe Subst -> Bool
    forall a. Maybe a -> Bool
    isJust (Kind -> Kind -> Maybe Subst
    tcMatchTy Kind
    ty1 Kind
    ty2)
        go_arg SpecArg
    UnspecType     SpecArg
    UnspecType     = Bool
    True
        go_arg (SpecDict {})  (SpecDict {})  = Bool
    True
        go_arg SpecArg
    UnspecArg      SpecArg
    UnspecArg      = Bool
    True
        go_arg SpecArg
    _              SpecArg
    _              = Bool
    False

    ----------------------
    splitDictBinds :: FloatedDictBinds -> IdSet -> (FloatedDictBinds, OrdList DictBind, IdSet)
    -- splitDictBinds dbs bndrs returns
    --   (free_dbs, dump_dbs, dump_set)
    -- where
    --   * dump_dbs depends, transitively on bndrs
    --   * free_dbs does not depend on bndrs
    --   * dump_set = bndrs `union` bndrs(dump_dbs)
    splitDictBinds :: FloatedDictBinds
    -> VarSet -> (FloatedDictBinds, OrdList DictBind, VarSet)
    splitDictBinds (FDB { fdb_binds :: FloatedDictBinds -> OrdList DictBind
    fdb_binds = OrdList DictBind
    dbs, fdb_bndrs :: FloatedDictBinds -> VarSet
    fdb_bndrs = VarSet
    bs }) VarSet
    bndr_set
       = (FDB { fdb_binds :: OrdList DictBind
    fdb_binds = OrdList DictBind
    free_dbs
              , fdb_bndrs :: VarSet
    fdb_bndrs = VarSet
    bs VarSet -> VarSet -> VarSet
    `minusVarSet` VarSet
    dump_set }
         , OrdList DictBind
    dump_dbs, VarSet
    dump_set)
       where
        (OrdList DictBind
    free_dbs, OrdList DictBind
    dump_dbs, VarSet
    dump_set)
          = ((OrdList DictBind, OrdList DictBind, VarSet)
     -> DictBind -> (OrdList DictBind, OrdList DictBind, VarSet))
    -> (OrdList DictBind, OrdList DictBind, VarSet)
    -> OrdList DictBind
    -> (OrdList DictBind, OrdList DictBind, VarSet)
    forall b a. (b -> a -> b) -> b -> OrdList a -> b
    forall (t :: * -> *) b a.
    Foldable t =>
    (b -> a -> b) -> b -> t a -> b
    foldl' (OrdList DictBind, OrdList DictBind, VarSet)
    -> DictBind -> (OrdList DictBind, OrdList DictBind, VarSet)
    split_db (OrdList DictBind
    forall a. OrdList a
    nilOL, OrdList DictBind
    forall a. OrdList a
    nilOL, VarSet
    bndr_set) OrdList DictBind
    dbs
                    -- Important that it's foldl' not foldr;
                    -- we're accumulating the set of dumped ids in dump_set

        split_db :: (OrdList DictBind, OrdList DictBind, VarSet)
    -> DictBind -> (OrdList DictBind, OrdList DictBind, VarSet)
    split_db (OrdList DictBind
    free_dbs, OrdList DictBind
    dump_dbs, VarSet
    dump_idset) DictBind
    db
            | DB { db_bind :: DictBind -> InBind
    db_bind = InBind
    bind, db_fvs :: DictBind -> VarSet
    db_fvs = VarSet
    fvs } <- DictBind
    db
            , VarSet
    dump_idset VarSet -> VarSet -> Bool
    `intersectsVarSet` VarSet
    fvs     -- Dump it
            = (OrdList DictBind
    free_dbs, OrdList DictBind
    dump_dbs OrdList DictBind -> DictBind -> OrdList DictBind
    forall a. OrdList a -> a -> OrdList a
    `snocOL` DictBind
    db,
               VarSet -> [Id] -> VarSet
    extendVarSetList VarSet
    dump_idset (InBind -> [Id]
    forall b. Bind b -> [b]
    bindersOf InBind
    bind))

            | Bool
    otherwise     -- Don't dump it
            = (OrdList DictBind
    free_dbs OrdList DictBind -> DictBind -> OrdList DictBind
    forall a. OrdList a -> a -> OrdList a
    `snocOL` DictBind
    db, OrdList DictBind
    dump_dbs, VarSet
    dump_idset)

    ----------------------
    deleteCallsMentioning :: VarSet -> CallDetails -> CallDetails
    -- Remove calls mentioning any Id in bndrs
    -- NB: The call is allowed to mention TyVars in bndrs
    --     Note [Specialising polymorphic dictionaries]
    --     ci_fvs are just the free /Ids/
    deleteCallsMentioning :: VarSet -> CallDetails -> CallDetails
    deleteCallsMentioning VarSet
    bndrs CallDetails
    calls
      = (CallInfoSet -> CallInfoSet) -> CallDetails -> CallDetails
    forall a b. (a -> b) -> DVarEnv a -> DVarEnv b
    mapDVarEnv ((CallInfo -> Bool) -> CallInfoSet -> CallInfoSet
    ciSetFilter CallInfo -> Bool
    keep_call) CallDetails
    calls
      where
        keep_call :: CallInfo -> Bool
    keep_call (CI { ci_fvs :: CallInfo -> VarSet
    ci_fvs = VarSet
    fvs }) = VarSet
    fvs VarSet -> VarSet -> Bool
    `disjointVarSet` VarSet
    bndrs

    deleteCallsFor :: [Id] -> CallDetails -> CallDetails
    -- Remove calls *for* bndrs
    deleteCallsFor :: [Id] -> CallDetails -> CallDetails
    deleteCallsFor [Id]
    bndrs CallDetails
    calls = CallDetails -> [Id] -> CallDetails
    forall a. DVarEnv a -> [Id] -> DVarEnv a
    delDVarEnvList CallDetails
    calls [Id]
    bndrs

    {-
    ************************************************************************
    *                                                                      *
    \subsubsection{Boring helper functions}
    *                                                                      *
    ************************************************************************
    -}

    type SpecM a = UniqSM a

    runSpecM :: SpecM a -> CoreM a
    runSpecM :: forall a. SpecM a -> CoreM a
    runSpecM SpecM a
    thing_inside
      = do { us <- CoreM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM
           ; return (initUs_ us thing_inside) }

    mapAndCombineSM :: (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM :: forall a b.
    (a -> SpecM (b, UsageDetails)) -> [a] -> SpecM ([b], UsageDetails)
    mapAndCombineSM a -> SpecM (b, UsageDetails)
    _ []     = ([b], UsageDetails) -> UniqSM ([b], UsageDetails)
    forall a. a -> UniqSM a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ([], UsageDetails
    emptyUDs)
    mapAndCombineSM a -> SpecM (b, UsageDetails)
    f (a
    x:[a]
    xs) = do (y, uds1) <- a -> SpecM (b, UsageDetails)
    f a
    x
                                  (ys, uds2) <- mapAndCombineSM f xs
                                  return (y:ys, uds1 `thenUDs` uds2)

    extendTvSubst :: SpecEnv -> TyVar -> Type -> SpecEnv
    extendTvSubst :: SpecEnv -> Id -> Kind -> SpecEnv
    extendTvSubst SpecEnv
    env Id
    tv Kind
    ty
      = SpecEnv
    env { se_subst = Core.extendTvSubst (se_subst env) tv ty }

    extendInScope :: SpecEnv -> OutId -> SpecEnv
    extendInScope :: SpecEnv -> Id -> SpecEnv
    extendInScope env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst }) Id
    bndr
      = SpecEnv
    env { se_subst = subst `Core.extendSubstInScope` bndr }

    zapSubst :: SpecEnv -> SpecEnv
    zapSubst :: SpecEnv -> SpecEnv
    zapSubst env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst })
      = SpecEnv
    env { se_subst = Core.zapSubst subst }

    substTy :: SpecEnv -> Type -> Type
    substTy :: SpecEnv -> Kind -> Kind
    substTy SpecEnv
    env Kind
    ty = Subst -> Kind -> Kind
    substTyUnchecked (SpecEnv -> Subst
    se_subst SpecEnv
    env) Kind
    ty

    substCo :: SpecEnv -> Coercion -> Coercion
    substCo :: SpecEnv -> Coercion -> Coercion
    substCo SpecEnv
    env Coercion
    co = HasDebugCallStack => Subst -> Coercion -> Coercion
    Subst -> Coercion -> Coercion
    Core.substCo (SpecEnv -> Subst
    se_subst SpecEnv
    env) Coercion
    co

    substBndr :: SpecEnv -> CoreBndr -> (SpecEnv, CoreBndr)
    substBndr :: SpecEnv -> Id -> (SpecEnv, Id)
    substBndr SpecEnv
    env Id
    bs = case Subst -> Id -> (Subst, Id)
    Core.substBndr (SpecEnv -> Subst
    se_subst SpecEnv
    env) Id
    bs of
                          (Subst
    subst', Id
    bs') -> (SpecEnv
    env { se_subst = subst' }, Id
    bs')

    substBndrs :: SpecEnv -> [CoreBndr] -> (SpecEnv, [CoreBndr])
    substBndrs :: SpecEnv -> [Id] -> (SpecEnv, [Id])
    substBndrs SpecEnv
    env [Id]
    bs = case Subst -> [Id] -> (Subst, [Id])
    forall (f :: * -> *).
    Traversable f =>
    Subst -> f Id -> (Subst, f Id)
    Core.substBndrs (SpecEnv -> Subst
    se_subst SpecEnv
    env) [Id]
    bs of
                          (Subst
    subst', [Id]
    bs') -> (SpecEnv
    env { se_subst = subst' }, [Id]
    bs')

    cloneBndrSM :: SpecEnv -> Id -> SpecM (SpecEnv, Id)
    -- Clone the binders of the bind; return new bind with the cloned binders
    -- Return the substitution to use for RHSs, and the one to use for the body
    -- Discards non-Stable unfoldings
    cloneBndrSM :: SpecEnv -> Id -> UniqSM (SpecEnv, Id)
    cloneBndrSM env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst }) Id
    bndr
      = do { us <- UniqSM UniqSupply
    forall (m :: * -> *). MonadUnique m => m UniqSupply
    getUniqueSupplyM
           ; let (subst', bndr') = Core.cloneIdBndr subst us bndr
           ; return (env { se_subst = subst' }, bndr') }

    cloneRecBndrsSM :: SpecEnv -> [Id] -> SpecM (SpecEnv, [Id])
    cloneRecBndrsSM :: SpecEnv -> [Id] -> UniqSM (SpecEnv, [Id])
    cloneRecBndrsSM env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst }) [Id]
    bndrs
      = do { (subst', bndrs') <- Subst -> [Id] -> UniqSM (Subst, [Id])
    forall (m :: * -> *).
    MonadUnique m =>
    Subst -> [Id] -> m (Subst, [Id])
    Core.cloneRecIdBndrs Subst
    subst [Id]
    bndrs
           ; let env' = SpecEnv
    env { se_subst = subst' }
           ; return (env', bndrs') }

    newDictBndr :: SpecEnv -> CoreBndr -> SpecM (SpecEnv, CoreBndr)
    -- Make up completely fresh binders for the dictionaries
    -- Their bindings are going to float outwards
    newDictBndr :: SpecEnv -> Id -> UniqSM (SpecEnv, Id)
    newDictBndr env :: SpecEnv
    env@(SE { se_subst :: SpecEnv -> Subst
    se_subst = Subst
    subst }) Id
    b
      = do { uniq <- UniqSM Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
           ; let n    = Id -> Name
    idName Id
    b
                 ty'  = Subst -> Kind -> Kind
    substTyUnchecked Subst
    subst (Id -> Kind
    idType Id
    b)
                 b'   = OccName -> Unique -> Kind -> Kind -> SrcSpan -> Id
    mkUserLocal (Name -> OccName
    nameOccName Name
    n) Unique
    uniq Kind
    ManyTy Kind
    ty' (Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    n)
                 env' = SpecEnv
    env { se_subst = subst `Core.extendSubstInScope` b' }
           ; pure (env', b') }

    newSpecIdSM :: Name -> Type -> IdDetails -> IdInfo -> SpecM Id
        -- Give the new Id a similar occurrence name to the old one
    newSpecIdSM :: Name -> Kind -> IdDetails -> IdInfo -> UniqSM Id
    newSpecIdSM Name
    old_name Kind
    new_ty IdDetails
    details IdInfo
    info
      = do  { uniq <- UniqSM Unique
    forall (m :: * -> *). MonadUnique m => m Unique
    getUniqueM
            ; let new_occ  = OccName -> OccName
    mkSpecOcc (Name -> OccName
    nameOccName Name
    old_name)
                  new_name = Unique -> OccName -> SrcSpan -> Name
    mkInternalName Unique
    uniq OccName
    new_occ  (Name -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan Name
    old_name)
            ; return (assert (not (isCoVarType new_ty)) $
                      mkLocalVar details new_name ManyTy new_ty info) }

    {-
                    Old (but interesting) stuff about unboxed bindings
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    What should we do when a value is specialised to a *strict* unboxed value?

            map_*_* f (x:xs) = let h = f x
                                   t = map f xs
                               in h:t

    Could convert let to case:

            map_*_Int# f (x:xs) = case f x of h# ->
                                  let t = map f xs
                                  in h#:t

    This may be undesirable since it forces evaluation here, but the value
    may not be used in all branches of the body. In the general case this
    transformation is impossible since the mutual recursion in a letrec
    cannot be expressed as a case.

    There is also a problem with top-level unboxed values, since our
    implementation cannot handle unboxed values at the top level.

    Solution: Lift the binding of the unboxed value and extract it when it
    is used:

            map_*_Int# f (x:xs) = let h = case (f x) of h# -> _Lift h#
                                      t = map f xs
                                  in case h of
                                     _Lift h# -> h#:t

    Now give it to the simplifier and the _Lifting will be optimised away.

    The benefit is that we have given the specialised "unboxed" values a
    very simple lifted semantics and then leave it up to the simplifier to
    optimise it --- knowing that the overheads will be removed in nearly
    all cases.

    In particular, the value will only be evaluated in the branches of the
    program which use it, rather than being forced at the point where the
    value is bound. For example:

            filtermap_*_* p f (x:xs)
              = let h = f x
                    t = ...
                in case p x of
                    True  -> h:t
                    False -> t
       ==>
            filtermap_*_Int# p f (x:xs)
              = let h = case (f x) of h# -> _Lift h#
                    t = ...
                in case p x of
                    True  -> case h of _Lift h#
                               -> h#:t
                    False -> t

    The binding for h can still be inlined in the one branch and the
    _Lifting eliminated.

    Question: When won't the _Lifting be eliminated?

    Answer: When they at the top-level (where it is necessary) or when
    inlining would duplicate work (or possibly code depending on
    options). However, the _Lifting will still be eliminated if the
    strictness analyser deems the lifted binding strict.
    -}