ghc-9.10.3: The GHC API

Safe Haskell | None
Language | GHC2021

GHC.Core.Utils

Contents

- Constructing expressions
- Taking expressions apart
- Properties of expressions
- Equality
- Manipulating data constructors and types
- Working with ticks
- InScopeSet things which work over CoreBinds
- StaticPtr
- Join points
- Tag inference
- unsafeEqualityProof
- Dumping stuff

Description

Commonly useful utilities for manipulating the Core language

Synopsis

- mkCast :: HasDebugCallStack => CoreExpr -> CoercionR -> CoreExpr
- mkCastMCo :: CoreExpr -> MCoercionR -> CoreExpr
- mkPiMCo :: Var -> MCoercionR -> MCoercionR
- mkTick :: CoreTickish -> CoreExpr -> CoreExpr
- mkTicks :: [CoreTickish] -> CoreExpr -> CoreExpr
- mkTickNoHNF :: CoreTickish -> CoreExpr -> CoreExpr
- tickHNFArgs :: CoreTickish -> CoreExpr -> CoreExpr
- bindNonRec :: HasDebugCallStack => Id -> CoreExpr -> CoreExpr -> CoreExpr
- needsCaseBinding :: HasDebugCallStack => Type -> CoreExpr -> Bool
- needsCaseBindingL :: Levity -> CoreExpr -> Bool
- mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
- mkDefaultCase :: CoreExpr -> Id -> CoreExpr -> CoreExpr
- mkSingleAltCase :: CoreExpr -> Id -> AltCon -> [Var] -> CoreExpr -> CoreExpr
- findDefault :: [Alt b] -> ([Alt b], Maybe (Expr b))
- addDefault :: [Alt b] -> Maybe (Expr b) -> [Alt b]
- findAlt :: AltCon -> [Alt b] -> Maybe (Alt b)
- isDefaultAlt :: Alt b -> Bool
- mergeAlts :: [Alt a] -> [Alt a] -> [Alt a]
- trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
- filterAlts :: TyCon -> [Type] -> [AltCon] -> [Alt b] -> ([AltCon], [Alt b])
- combineIdenticalAlts :: [AltCon] -> [CoreAlt] -> (Bool, [AltCon], [CoreAlt])
- refineDefaultAlt :: [Unique] -> Mult -> TyCon -> [Type] -> [AltCon] -> [CoreAlt] -> (Bool, [CoreAlt])
- scaleAltsBy :: Mult -> [CoreAlt] -> [CoreAlt]
- exprType :: HasDebugCallStack => CoreExpr -> Type
- coreAltType :: CoreAlt -> Type
- coreAltsType :: [CoreAlt] -> Type
- mkLamType :: HasDebugCallStack => Var -> Type -> Type
- mkLamTypes :: [Var] -> Type -> Type
- mkFunctionType :: HasDebugCallStack => Mult -> Type -> Type -> Type
- exprIsTrivial :: CoreExpr -> Bool
- getIdFromTrivialExpr :: HasDebugCallStack => CoreExpr -> Id
- getIdFromTrivialExpr_maybe :: CoreExpr -> Maybe Id
- trivial_expr_fold :: (Id -> r) -> (Literal -> r) -> r -> r -> CoreExpr -> r
- exprIsDupable :: Platform -> CoreExpr -> Bool
- exprIsCheap :: CoreExpr -> Bool
- exprIsExpandable :: CoreExpr -> Bool
- exprIsCheapX :: CheapAppFun -> CoreExpr -> Bool
- type CheapAppFun = Id -> Arity -> Bool
- exprIsHNF :: CoreExpr -> Bool
- exprOkForSpeculation :: CoreExpr -> Bool
- exprOkToDiscard :: CoreExpr -> Bool
- exprOkForSpecEval :: (Id -> Bool) -> CoreExpr -> Bool
- exprIsWorkFree :: CoreExpr -> Bool
- exprIsConLike :: CoreExpr -> Bool
- isCheapApp :: CheapAppFun
- isExpandableApp :: CheapAppFun
- isSaturatedConApp :: CoreExpr -> Bool
- exprIsTickedString :: CoreExpr -> Bool
- exprIsTickedString_maybe :: CoreExpr -> Maybe ByteString
- exprIsTopLevelBindable :: CoreExpr -> Type -> Bool
- altsAreExhaustive :: [Alt b] -> Bool
- etaExpansionTick :: forall (pass :: TickishPass). Id -> GenTickish pass -> Bool
- cheapEqExpr :: Expr b -> Expr b -> Bool
- cheapEqExpr' :: (CoreTickish -> Bool) -> Expr b -> Expr b -> Bool
- diffBinds :: Bool -> RnEnv2 -> [(Var, CoreExpr)] -> [(Var, CoreExpr)] -> ([SDoc], RnEnv2)
- exprToType :: CoreExpr -> Type
- applyTypeToArgs :: HasDebugCallStack => SDoc -> Type -> [CoreExpr] -> Type
- dataConRepInstPat :: [Unique] -> Mult -> DataCon -> [Type] -> ([TyCoVar], [Id])
- dataConRepFSInstPat :: [FastString] -> [Unique] -> Mult -> DataCon -> [Type] -> ([TyCoVar], [Id])
- isEmptyTy :: Type -> Bool
- normSplitTyConApp_maybe :: FamInstEnvs -> Type -> Maybe (TyCon, [Type], Coercion)
- stripTicksTop :: (CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b)
- stripTicksTopE :: (CoreTickish -> Bool) -> Expr b -> Expr b
- stripTicksTopT :: (CoreTickish -> Bool) -> Expr b -> [CoreTickish]
- stripTicksE :: (CoreTickish -> Bool) -> Expr b -> Expr b
- stripTicksT :: (CoreTickish -> Bool) -> Expr b -> [CoreTickish]
- mkInScopeSetBndrs :: [CoreBind] -> InScopeSet
- extendInScopeSetBind :: InScopeSet -> CoreBind -> InScopeSet
- extendInScopeSetBndrs :: InScopeSet -> [CoreBind] -> InScopeSet
- collectMakeStaticArgs :: CoreExpr -> Maybe (CoreExpr, Type, CoreExpr, CoreExpr)
- isJoinBind :: CoreBind -> Bool
- mkStrictFieldSeqs :: [(Id, StrictnessMark)] -> CoreExpr -> CoreExpr
- shouldStrictifyIdForCbv :: Var -> Bool
- shouldUseCbvForId :: Var -> Bool
- isUnsafeEqualityCase :: CoreExpr -> Id -> [CoreAlt] -> Maybe CoreExpr
- dumpIdInfoOfProgram :: Bool -> (IdInfo -> SDoc) -> CoreProgram -> SDoc

# Constructing expressions

mkCast :: HasDebugCallStack => CoreExpr -> CoercionR -> CoreExpr Source #

Wrap the given expression in the coercion safely, dropping identity coercions and coalescing nested coercions

mkCastMCo :: CoreExpr -> MCoercionR -> CoreExpr Source #

mkPiMCo :: Var -> MCoercionR -> MCoercionR Source #

mkTick :: CoreTickish -> CoreExpr -> CoreExpr Source #

Wraps the given expression in the source annotation, dropping the annotation if possible.

mkTicks :: [CoreTickish] -> CoreExpr -> CoreExpr Source #

mkTickNoHNF :: CoreTickish -> CoreExpr -> CoreExpr Source #

tickHNFArgs :: CoreTickish -> CoreExpr -> CoreExpr Source #

bindNonRec :: HasDebugCallStack => Id -> CoreExpr -> CoreExpr -> CoreExpr Source #

`bindNonRec x r b` produces either:

    let x = r in b

or:

    case r of x { _DEFAULT_ -> b }

depending on whether we have to use a `case` or `let` binding for the expression (see `needsCaseBinding`). It's used by the desugarer to avoid building bindings that give Core Lint a heart attack, although actually the simplifier deals with them perfectly well. See also `mkCoreLet`

needsCaseBinding :: HasDebugCallStack => Type -> CoreExpr -> Bool Source #

`needsCaseBinding` tests whether we have to use a `case` rather than `let` binding for this expression as per the invariants of `CoreExpr`: see GHC.Core (needsCaseBinding ty rhs) requires that `ty` has a well-defined levity, else `typeLevity ty` will fail; but that should be the case because `needsCaseBinding` is only called once typechecking is complete

needsCaseBindingL :: Levity -> CoreExpr -> Bool Source #

mkAltExpr Source #

Arguments

:: AltCon | Case alternative constructor
-> [CoreBndr] | Things bound by the pattern match
-> [Type] | The type arguments to the case alternative
-> CoreExpr |

This guy constructs the value that the scrutinee must have given that you are in one particular branch of a case

mkDefaultCase :: CoreExpr -> Id -> CoreExpr -> CoreExpr Source #

mkSingleAltCase :: CoreExpr -> Id -> AltCon -> [Var] -> CoreExpr -> CoreExpr Source #

# Taking expressions apart

findDefault :: [Alt b] -> ([Alt b], Maybe (Expr b)) Source #

Extract the default case alternative

addDefault :: [Alt b] -> Maybe (Expr b) -> [Alt b] Source #

findAlt :: AltCon -> [Alt b] -> Maybe (Alt b) Source #

Find the case alternative corresponding to a particular constructor: panics if no such constructor exists

isDefaultAlt :: Alt b -> Bool Source #

mergeAlts :: [Alt a] -> [Alt a] -> [Alt a] Source #

Merge alternatives preserving order; alternatives in the first argument shadow ones in the second

trimConArgs :: AltCon -> [CoreArg] -> [CoreArg] Source #

Given:

    case (C a b x y) of
           C b x y -> ...

We want to drop the leading type argument of the scrutinee leaving the arguments to match against the pattern

filterAlts Source #

Arguments

:: TyCon | Type constructor of scrutinee's type (used to prune possibilities)
-> [Type] | And its type arguments
-> [AltCon] | `imposs_cons`: constructors known to be impossible due to the form of the scrutinee
-> [Alt b] | Alternatives
-> ([AltCon], [Alt b]) |

combineIdenticalAlts :: [AltCon] -> [CoreAlt] -> (Bool, [AltCon], [CoreAlt]) Source #

refineDefaultAlt Source #

Arguments

:: [Unique] | Uniques for constructing new binders
-> Mult | Multiplicity annotation of the case expression
-> TyCon | Type constructor of scrutinee's type
-> [Type] | Type arguments of scrutinee's type
-> [AltCon] | Constructors that cannot match the DEFAULT (if any)
-> [CoreAlt] |
-> (Bool, [CoreAlt]) | `True`, if a default alt was replaced with a `DataAlt`

Refine the default alternative to a `DataAlt`, if there is a unique way to do so. See Note [Refine DEFAULT case alternatives]

scaleAltsBy :: Mult -> [CoreAlt] -> [CoreAlt] Source #

# Properties of expressions

exprType :: HasDebugCallStack => CoreExpr -> Type Source #

Recover the type of a well-typed Core expression. Fails when applied to the actual `Type` expression as it cannot really be said to have a type

coreAltType :: CoreAlt -> Type Source #

Returns the type of the alternatives right hand side

coreAltsType :: [CoreAlt] -> Type Source #

Returns the type of the first alternative, which should be the same as for all alternatives

mkLamType :: HasDebugCallStack => Var -> Type -> Type Source #

Makes a `(->)` type or an implicit forall type, depending on whether it is given a type variable or a term variable. This is used, for example, when producing the type of a lambda.

mkLamTypes :: [Var] -> Type -> Type Source #

`mkLamType` for multiple type or value arguments

mkFunctionType :: HasDebugCallStack => Mult -> Type -> Type -> Type Source #

This one works out the FunTyFlag from the argument type See GHC.Types.Var Note [FunTyFlag]

exprIsTrivial :: CoreExpr -> Bool Source #

getIdFromTrivialExpr :: HasDebugCallStack => CoreExpr -> Id Source #

getIdFromTrivialExpr_maybe :: CoreExpr -> Maybe Id Source #

trivial_expr_fold :: (Id -> r) -> (Literal -> r) -> r -> r -> CoreExpr -> r Source #

The worker function for Note [exprIsTrivial] and Note [getIdFromTrivialExpr] This is meant to have the code of both functions in one place and make it easy to derive custom predicates.

(trivial_expr_fold k_id k_triv k_not_triv e) * returns (k_id x) if `e` is a variable `x` (with trivial wrapping) * returns (k_lit x) if `e` is a trivial literal `l` (with trivial wrapping) * returns k_triv if `e` is a literal, type, or coercion (with trivial wrapping) * returns k_not_triv otherwise

where "trivial wrapping" is * Type application or abstraction * Ticks other than `tickishIsCode` * `case e of {}` an empty case

exprIsDupable :: Platform -> CoreExpr -> Bool Source #

exprIsCheap :: CoreExpr -> Bool Source #

exprIsExpandable :: CoreExpr -> Bool Source #

exprIsCheapX :: CheapAppFun -> CoreExpr -> Bool Source #

type CheapAppFun = Id -> Arity -> Bool Source #

exprIsHNF :: CoreExpr -> Bool Source #

exprIsHNF returns true for expressions that are certainly already evaluated to head normal form. This is used to decide whether it's ok to perform case-to-let for lifted expressions, which changes:

    case x of x' { _ -> e }

into:

    let x' = x in e

and in so doing makes the binding lazy.

So, it does not treat variables as evaluated, unless they say they are. However, it does treat partial applications and constructor applications as values, even if their arguments are non-trivial, provided the argument type is lifted. For example, both of these are values:

    (:) (f x) (map f xs)
    map (...redex...)

because `seq` on such things completes immediately.

For unlifted argument types, we have to be careful:

    C (f x :: Int#)

Suppose `f x` diverges; then `C (f x)` is not a value. We check for this using needsCaseBinding below

exprOkForSpeculation :: CoreExpr -> Bool Source #

To a first approximation, `exprOkForSpeculation` returns True of an expression that is:

- Safe to evaluate even if normal order eval might not evaluate the expression at all, and
- Safe not to evaluate even if normal order would do so

More specifically, this means that: * A: Evaluation of the expression reaches weak-head-normal-form, * B: soon, * C: without causing a write side effect (e.g. writing a mutable variable).

In particular, an expression that may * throw a synchronous Haskell exception, or * risk an unchecked runtime exception (e.g. array out of bounds, divide by zero) is not considered OK-for-speculation, as these violate condition A.

For `exprOkToDiscard`, condition A is weakened to allow expressions that might risk an unchecked runtime exception but must otherwise reach weak-head-normal-form. (Note that `exprOkForSpeculation` implies `exprOkToDiscard`)

But in fact both functions are a bit more conservative than the above, in at least the following ways:

- W1: We do not take advantage of already-evaluated lifted variables. As a result, `exprIsHNF` DOES NOT imply `exprOkForSpeculation`; if `y` is a case-binder of lifted type, then `exprIsHNF y` is `True`, while `exprOkForSpeculation y` is `False`. See Note [exprOkForSpeculation and evaluated variables] for why.
- W2: Read-effects on mutable variables are currently also included. See Note [Classifying primop effects] GHC.Builtin.PrimOps.
- W3: Currently, `exprOkForSpeculation` always returns `False` for let-expressions. Lets can be stacked deeply, so we just give up. In any case, the argument of `exprOkForSpeculation` is usually in a strict context, so any lets will have been floated away.

As an example of the considerations in this test, consider:

    let x = case y# +# 1# of { r# -> I# r# }
    in E

being translated to:

    case y# +# 1# of { r# ->
       let x = I# r#
       in E
    }

We can only do this if the `y# +# 1#` is ok for speculation: it has no side effects, and can't diverge or raise an exception.

See also Note [Classifying primop effects] in GHC.Builtin.PrimOps and Note [Transformations affected by primop effects].

`exprOkForSpeculation` is used to define Core's let-can-float invariant. (See Note [Core let-can-float invariant] in GHC.Core.) It is therefore frequently called on arguments of unlifted type, especially via `needsCaseBinding`. But it is sometimes called on expressions of lifted type as well. For example, see Note [Speculative evaluation] in GHC.CoreToStg.Prep.

exprOkToDiscard :: CoreExpr -> Bool Source #

To a first approximation, `exprOkForSpeculation` returns True of an expression that is:

- Safe to evaluate even if normal order eval might not evaluate the expression at all, and
- Safe not to evaluate even if normal order would do so

More specifically, this means that: * A: Evaluation of the expression reaches weak-head-normal-form, * B: soon, * C: without causing a write side effect (e.g. writing a mutable variable).

In particular, an expression that may * throw a synchronous Haskell exception, or * risk an unchecked runtime exception (e.g. array out of bounds, divide by zero) is not considered OK-for-speculation, as these violate condition A.

For `exprOkToDiscard`, condition A is weakened to allow expressions that might risk an unchecked runtime exception but must otherwise reach weak-head-normal-form. (Note that `exprOkForSpeculation` implies `exprOkToDiscard`)

But in fact both functions are a bit more conservative than the above, in at least the following ways:

- W1: We do not take advantage of already-evaluated lifted variables. As a result, `exprIsHNF` DOES NOT imply `exprOkForSpeculation`; if `y` is a case-binder of lifted type, then `exprIsHNF y` is `True`, while `exprOkForSpeculation y` is `False`. See Note [exprOkForSpeculation and evaluated variables] for why.
- W2: Read-effects on mutable variables are currently also included. See Note [Classifying primop effects] GHC.Builtin.PrimOps.
- W3: Currently, `exprOkForSpeculation` always returns `False` for let-expressions. Lets can be stacked deeply, so we just give up. In any case, the argument of `exprOkForSpeculation` is usually in a strict context, so any lets will have been floated away.

As an example of the considerations in this test, consider:

    let x = case y# +# 1# of { r# -> I# r# }
    in E

being translated to:

    case y# +# 1# of { r# ->
       let x = I# r#
       in E
    }

We can only do this if the `y# +# 1#` is ok for speculation: it has no side effects, and can't diverge or raise an exception.

See also Note [Classifying primop effects] in GHC.Builtin.PrimOps and Note [Transformations affected by primop effects].

`exprOkForSpeculation` is used to define Core's let-can-float invariant. (See Note [Core let-can-float invariant] in GHC.Core.) It is therefore frequently called on arguments of unlifted type, especially via `needsCaseBinding`. But it is sometimes called on expressions of lifted type as well. For example, see Note [Speculative evaluation] in GHC.CoreToStg.Prep.

exprOkForSpecEval :: (Id -> Bool) -> CoreExpr -> Bool Source #

A special version of `exprOkForSpeculation` used during Note [Speculative evaluation]. When the predicate arg `fun_ok` returns False for `b`, then `b` is never considered ok-for-spec.

exprIsWorkFree :: CoreExpr -> Bool Source #

exprIsConLike :: CoreExpr -> Bool Source #

Similar to `exprIsHNF` but includes CONLIKE functions as well as data constructors. Conlike arguments are considered interesting by the inliner.

isCheapApp :: CheapAppFun Source #

isExpandableApp :: CheapAppFun Source #

isSaturatedConApp :: CoreExpr -> Bool Source #

exprIsTickedString :: CoreExpr -> Bool Source #

Check if the expression is zero or more Ticks wrapped around a literal string.

exprIsTickedString_maybe :: CoreExpr -> Maybe ByteString Source #

Extract a literal string from an expression that is zero or more Ticks wrapped around a literal string. Returns Nothing if the expression has a different shape. Used to "look through" Ticks in places that need to handle literal strings.

exprIsTopLevelBindable :: CoreExpr -> Type -> Bool Source #

Can we bind this `CoreExpr` at the top level?

altsAreExhaustive :: [Alt b] -> Bool Source #

etaExpansionTick :: forall (pass :: TickishPass). Id -> GenTickish pass -> Bool Source #

Should we look past this tick when eta-expanding the given function?

See Note [Ticks and mandatory eta expansion] Takes the function we are applying as argument.

# Equality

cheapEqExpr :: Expr b -> Expr b -> Bool Source #

A cheap equality test which bales out fast! If it returns `True` the arguments are definitely equal, otherwise, they may or may not be equal.

cheapEqExpr' :: (CoreTickish -> Bool) -> Expr b -> Expr b -> Bool Source #

Cheap expression equality test, can ignore ticks by type.

diffBinds :: Bool -> RnEnv2 -> [(Var, CoreExpr)] -> [(Var, CoreExpr)] -> ([SDoc], RnEnv2) Source #

Finds differences between core bindings, see `diffExpr`.

The main problem here is that while we expect the binds to have the same order in both lists, this is not guaranteed. To do this properly we'd either have to do some sort of unification or check all possible mappings, which would be seriously expensive. So instead we simply match single bindings as far as we can. This leaves us just with mutually recursive and/or mismatching bindings, which we then speculatively match by ordering them. It's by no means perfect, but gets the job done well enough.

Only used in GHC.Core.Lint.lintAnnots

# Manipulating data constructors and types

exprToType :: CoreExpr -> Type Source #

If the expression is a `Type`, converts. Otherwise, panics. NB: This does not convert `Coercion` to `CoercionTy`.

applyTypeToArgs :: HasDebugCallStack => SDoc -> Type -> [CoreExpr] -> Type Source #

Determines the type resulting from applying an expression with given type

dataConRepInstPat :: [Unique] -> Mult -> DataCon -> [Type] -> ([TyCoVar], [Id]) Source #

dataConRepFSInstPat :: [FastString] -> [Unique] -> Mult -> DataCon -> [Type] -> ([TyCoVar], [Id]) Source #

isEmptyTy :: Type -> Bool Source #

True if the type has no non-bottom elements, e.g. when it is an empty datatype, or a GADT with non-satisfiable type parameters, e.g. Int :~: Bool. See Note [Bottoming expressions]

See Note [No alternatives lint check] for another use of this function.

normSplitTyConApp_maybe :: FamInstEnvs -> Type -> Maybe (TyCon, [Type], Coercion) Source #

If `normSplitTyConApp_maybe _ ty = Just (tc, tys, co)` then `ty |> co = tc tys`. It's `splitTyConApp_maybe`, but looks through coercions via `topNormaliseType_maybe`. Hence the "norm" prefix.

# Working with ticks

stripTicksTop :: (CoreTickish -> Bool) -> Expr b -> ([CoreTickish], Expr b) Source #

Strip ticks satisfying a predicate from top of an expression

stripTicksTopE :: (CoreTickish -> Bool) -> Expr b -> Expr b Source #

Strip ticks satisfying a predicate from top of an expression, returning the remaining expression

stripTicksTopT :: (CoreTickish -> Bool) -> Expr b -> [CoreTickish] Source #

Strip ticks satisfying a predicate from top of an expression, returning the ticks

stripTicksE :: (CoreTickish -> Bool) -> Expr b -> Expr b Source #

Completely strip ticks satisfying a predicate from an expression. Note this is O(n) in the size of the expression!

stripTicksT :: (CoreTickish -> Bool) -> Expr b -> [CoreTickish] Source #

# InScopeSet things which work over CoreBinds

mkInScopeSetBndrs :: [CoreBind] -> InScopeSet Source #

extendInScopeSetBind :: InScopeSet -> CoreBind -> InScopeSet Source #

extendInScopeSetBndrs :: InScopeSet -> [CoreBind] -> InScopeSet Source #

# StaticPtr

collectMakeStaticArgs :: CoreExpr -> Maybe (CoreExpr, Type, CoreExpr, CoreExpr) Source #

`collectMakeStaticArgs (makeStatic t srcLoc e)` yields `Just (makeStatic, t, srcLoc, e)`.

Returns `Nothing` for every other expression.

# Join points

isJoinBind :: CoreBind -> Bool Source #

Does this binding bind a join point (or a recursive group of join points)?

# Tag inference

mkStrictFieldSeqs :: [(Id, StrictnessMark)] -> CoreExpr -> CoreExpr Source #

shouldStrictifyIdForCbv :: Var -> Bool Source #

Do we expect there to be any benefit if we make this var strict in order for it to get treated as as cbv argument? See Note [Which Ids should be strictified] See Note [CBV Function Ids] for more background.

shouldUseCbvForId :: Var -> Bool Source #

# unsafeEqualityProof

isUnsafeEqualityCase :: CoreExpr -> Id -> [CoreAlt] -> Maybe CoreExpr Source #

# Dumping stuff

dumpIdInfoOfProgram :: Bool -> (IdInfo -> SDoc) -> CoreProgram -> SDoc Source #