Safe Haskell | None |
---|---|

Language | Haskell2010 |

Commonly useful utilites for manipulating the Core language

- mkCast :: CoreExpr -> Coercion -> CoreExpr
- mkTick :: Tickish Id -> CoreExpr -> CoreExpr
- mkTicks :: [Tickish Id] -> CoreExpr -> CoreExpr
- mkTickNoHNF :: Tickish Id -> CoreExpr -> CoreExpr
- tickHNFArgs :: Tickish Id -> CoreExpr -> CoreExpr
- bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
- needsCaseBinding :: Type -> CoreExpr -> Bool
- mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
- findDefault :: [(AltCon, [a], b)] -> ([(AltCon, [a], b)], Maybe b)
- addDefault :: [(AltCon, [a], b)] -> Maybe b -> [(AltCon, [a], b)]
- findAlt :: AltCon -> [(AltCon, a, b)] -> Maybe (AltCon, a, b)
- isDefaultAlt :: (AltCon, a, b) -> Bool
- mergeAlts :: [(AltCon, a, b)] -> [(AltCon, a, b)] -> [(AltCon, a, b)]
- trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
- filterAlts :: TyCon -> [Type] -> [AltCon] -> [(AltCon, [Var], a)] -> ([AltCon], [(AltCon, [Var], a)])
- combineIdenticalAlts :: [AltCon] -> [CoreAlt] -> (Bool, [AltCon], [CoreAlt])
- refineDefaultAlt :: [Unique] -> TyCon -> [Type] -> [AltCon] -> [CoreAlt] -> (Bool, [CoreAlt])
- exprType :: CoreExpr -> Type
- coreAltType :: CoreAlt -> Type
- coreAltsType :: [CoreAlt] -> Type
- exprIsDupable :: DynFlags -> CoreExpr -> Bool
- exprIsTrivial :: CoreExpr -> Bool
- getIdFromTrivialExpr :: CoreExpr -> Id
- exprIsBottom :: CoreExpr -> Bool
- getIdFromTrivialExpr_maybe :: CoreExpr -> Maybe Id
- exprIsCheap :: CoreExpr -> Bool
- exprIsExpandable :: CoreExpr -> Bool
- exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
- type CheapAppFun = Id -> Int -> Bool
- exprIsHNF :: CoreExpr -> Bool
- exprOkForSpeculation :: Expr b -> Bool
- exprOkForSideEffects :: Expr b -> Bool
- exprIsWorkFree :: CoreExpr -> Bool
- exprIsBig :: Expr b -> Bool
- exprIsConLike :: CoreExpr -> Bool
- rhsIsStatic :: Platform -> (Name -> Bool) -> (Integer -> CoreExpr) -> CoreExpr -> Bool
- isCheapApp :: CheapAppFun
- isExpandableApp :: CheapAppFun
- cheapEqExpr :: Expr b -> Expr b -> Bool
- cheapEqExpr' :: (Tickish Id -> Bool) -> Expr b -> Expr b -> Bool
- eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
- diffExpr :: Bool -> RnEnv2 -> CoreExpr -> CoreExpr -> [SDoc]
- diffBinds :: Bool -> RnEnv2 -> [(Var, CoreExpr)] -> [(Var, CoreExpr)] -> ([SDoc], RnEnv2)
- tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
- exprToType :: CoreExpr -> Type
- exprToCoercion_maybe :: CoreExpr -> Maybe Coercion
- applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
- applyTypeToArg :: Type -> CoreExpr -> Type
- dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
- dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
- isEmptyTy :: Type -> Bool
- stripTicksTop :: (Tickish Id -> Bool) -> Expr b -> ([Tickish Id], Expr b)
- stripTicksTopE :: (Tickish Id -> Bool) -> Expr b -> Expr b
- stripTicksTopT :: (Tickish Id -> Bool) -> Expr b -> [Tickish Id]
- stripTicksE :: (Tickish Id -> Bool) -> Expr b -> Expr b
- stripTicksT :: (Tickish Id -> Bool) -> Expr b -> [Tickish Id]

# Constructing expressions

mkCast :: CoreExpr -> Coercion -> CoreExpr Source #

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

mkTick :: Tickish Id -> CoreExpr -> CoreExpr Source #

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

bindNonRec :: 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`

:: 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

# Taking expressions apart

findDefault :: [(AltCon, [a], b)] -> ([(AltCon, [a], b)], Maybe b) Source #

Extract the default case alternative

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

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

isDefaultAlt :: (AltCon, a, b) -> Bool Source #

mergeAlts :: [(AltCon, a, b)] -> [(AltCon, a, b)] -> [(AltCon, a, b)] 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

refineDefaultAlt :: [Unique] -> TyCon -> [Type] -> [AltCon] -> [CoreAlt] -> (Bool, [CoreAlt]) Source #

# Properties of expressions

exprType :: 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

exprIsTrivial :: CoreExpr -> Bool Source #

getIdFromTrivialExpr :: CoreExpr -> Id Source #

exprIsBottom :: CoreExpr -> Bool Source #

exprIsCheap :: CoreExpr -> Bool Source #

exprIsExpandable :: CoreExpr -> Bool Source #

exprIsCheap' :: CheapAppFun -> CoreExpr -> 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 change:

case x of _ -> e

into:

e

and to decide whether it's safe to discard a `seq`

.

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. However this can't
happen: see CoreSyn. This invariant states that arguments of
unboxed type must be ok-for-speculation (or trivial).

exprOkForSpeculation :: Expr b -> Bool Source #

`exprOkForSpeculation`

returns True of an expression that is:

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

It is usually called on arguments of unlifted type, but not always
In particular, Simplify.rebuildCase calls it on lifted types
when a 'case' is a plain `seq`

. See the example in
Note [exprOkForSpeculation: case expressions] below

Precisely, it returns `True`

iff:
a) The expression guarantees to terminate,
b) soon,
c) without causing a write side effect (e.g. writing a mutable variable)
d) without throwing a Haskell exception
e) without risking an unchecked runtime exception (array out of bounds,
divide by zero)

For `exprOkForSideEffects`

the list is the same, but omitting (e).

Note that exprIsHNF implies exprOkForSpeculation exprOkForSpeculation implies exprOkForSideEffects

See Note [PrimOp can_fail and has_side_effects] in PrimOp and Note [Implementation: how can_fail/has_side_effects affect transformations]

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.

exprOkForSideEffects :: Expr b -> Bool Source #

`exprOkForSpeculation`

returns True of an expression that is:

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

It is usually called on arguments of unlifted type, but not always
In particular, Simplify.rebuildCase calls it on lifted types
when a 'case' is a plain `seq`

. See the example in
Note [exprOkForSpeculation: case expressions] below

Precisely, it returns `True`

iff:
a) The expression guarantees to terminate,
b) soon,
c) without causing a write side effect (e.g. writing a mutable variable)
d) without throwing a Haskell exception
e) without risking an unchecked runtime exception (array out of bounds,
divide by zero)

For `exprOkForSideEffects`

the list is the same, but omitting (e).

Note that exprIsHNF implies exprOkForSpeculation exprOkForSpeculation implies exprOkForSideEffects

See Note [PrimOp can_fail and has_side_effects] in PrimOp and Note [Implementation: how can_fail/has_side_effects affect transformations]

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.

exprIsWorkFree :: CoreExpr -> Bool Source #

exprIsBig :: Expr b -> Bool Source #

Returns `True`

of expressions that are too big to be compared by `cheapEqExpr`

exprIsConLike :: CoreExpr -> Bool Source #

Similar to `exprIsHNF`

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

rhsIsStatic :: Platform -> (Name -> Bool) -> (Integer -> CoreExpr) -> CoreExpr -> Bool Source #

This function is called only on *top-level* right-hand sides.
Returns `True`

if the RHS can be allocated statically in the output,
with no thunks involved at all.

# 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.

See also `exprIsBig`

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

Cheap expression equality test, can ignore ticks by type.

diffExpr :: Bool -> RnEnv2 -> CoreExpr -> CoreExpr -> [SDoc] Source #

Finds differences between core expressions, modulo alpha and
renaming. Setting `top`

means that the `IdInfo`

of bindings will be
checked for differences as well.

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 specuatively match by ordering them. It's by no means perfect, but gets the job done well enough.

# Eta reduction

# Manipulating data constructors and types

exprToType :: CoreExpr -> Type Source #

exprToCoercion_maybe :: CoreExpr -> Maybe Coercion Source #

If the expression is a `Coercion`

, converts.

applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type Source #

A more efficient version of `applyTypeToArg`

when we have several arguments.
The first argument is just for debugging, and gives some context

applyTypeToArg :: Type -> CoreExpr -> Type Source #

Determines the type resulting from applying an expression with given type to a given argument expression

dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [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.

# Working with ticks

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

Strip ticks satisfying a predicate from top of an expression

stripTicksTopE :: (Tickish Id -> Bool) -> Expr b -> Expr b Source #

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

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

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