Commonly useful utilites for manipulating the Core language
- mkSCC :: CostCentre -> Expr b -> Expr b
- mkCoerce :: Coercion -> CoreExpr -> CoreExpr
- mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
- bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
- needsCaseBinding :: Type -> CoreExpr -> Bool
- mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
- mkPiType :: EvVar -> Type -> Type
- mkPiTypes :: [EvVar] -> Type -> Type
- findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
- findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
- isDefaultAlt :: CoreAlt -> Bool
- mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
- trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
- exprType :: CoreExpr -> Type
- coreAltType :: CoreAlt -> Type
- coreAltsType :: [CoreAlt] -> Type
- exprIsDupable :: CoreExpr -> Bool
- exprIsTrivial :: CoreExpr -> Bool
- exprIsCheap :: CoreExpr -> Bool
- exprIsExpandable :: CoreExpr -> Bool
- exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
- type CheapAppFun = Id -> Int -> Bool
- exprIsHNF :: CoreExpr -> Bool
- exprOkForSpeculation :: CoreExpr -> Bool
- exprIsBig :: Expr b -> Bool
- exprIsConLike :: CoreExpr -> Bool
- rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
- isCheapApp :: CheapAppFun
- isExpandableApp :: CheapAppFun
- coreBindsSize :: [CoreBind] -> Int
- exprSize :: CoreExpr -> Int
- hashExpr :: CoreExpr -> Int
- cheapEqExpr :: Expr b -> Expr b -> Bool
- eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
- eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
- tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
- applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
- applyTypeToArg :: Type -> CoreExpr -> Type
- dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
- dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
- dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
Constructing expressions
mkSCC :: CostCentre -> Expr b -> Expr bSource
Wraps the given expression in the cost centre unless in a way that maximises their utility to the user
mkCoerce :: Coercion -> CoreExpr -> CoreExprSource
Wrap the given expression in the coercion safely, coalescing nested coercions
mkCoerceI :: CoercionI -> CoreExpr -> CoreExprSource
Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExprSource
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 MkCore.mkCoreLet
needsCaseBinding :: Type -> CoreExpr -> BoolSource
:: 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
mkPiType :: EvVar -> Type -> TypeSource
Makes a (->)
type or a forall type, depending
on whether it is given a type variable or a term variable.
Taking expressions apart
findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAltSource
Find the case alternative corresponding to a particular constructor: panics if no such constructor exists
isDefaultAlt :: CoreAlt -> BoolSource
mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]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 agains the pattern
Properties of expressions
exprType :: CoreExpr -> TypeSource
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 -> TypeSource
Returns the type of the alternatives right hand side
coreAltsType :: [CoreAlt] -> TypeSource
Returns the type of the first alternative, which should be the same as for all alternatives
exprIsDupable :: CoreExpr -> BoolSource
exprIsTrivial :: CoreExpr -> BoolSource
exprIsCheap :: CoreExpr -> BoolSource
exprIsCheap' :: CheapAppFun -> CoreExpr -> BoolSource
type CheapAppFun = Id -> Int -> BoolSource
exprIsHNF :: CoreExpr -> BoolSource
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 :: CoreExpr -> BoolSource
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
Precisely, it returns True
iff:
- The expression guarantees to terminate, * soon, * without raising an exception, * without causing a side effect (e.g. writing a mutable variable)
Note that if exprIsHNF e
, then exprOkForSpecuation e
.
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.
exprIsBig :: Expr b -> BoolSource
Returns True
of expressions that are too big to be compared by cheapEqExpr
exprIsConLike :: CoreExpr -> BoolSource
Similar to exprIsHNF
but includes CONLIKE functions as well as
data constructors. Conlike arguments are considered interesting by the
inliner.
rhsIsStatic :: (Name -> Bool) -> CoreExpr -> BoolSource
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.
Expression and bindings size
coreBindsSize :: [CoreBind] -> IntSource
exprSize :: CoreExpr -> IntSource
A measure of the size of the expressions, strictly greater than 0 It also forces the expression pretty drastically as a side effect
Hashing
hashExpr :: CoreExpr -> IntSource
Two expressions that hash to the same Int
may be equal (but may not be)
Two expressions that hash to the different Ints are definitely unequal.
The emphasis is on a crude, fast hash, rather than on high precision.
But unequal here means "not identical"; two alpha-equivalent expressions may hash to the different Ints.
We must be careful that \x.x
and \y.y
map to the same hash code,
(at least if we want the above invariant to be true).
Equality
cheapEqExpr :: Expr b -> Expr b -> BoolSource
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
eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> BoolSource
Compares expressions for equality, modulo alpha. Does not look through newtypes or predicate types Used in rule matching, and also CSE
Eta reduction
Manipulating data constructors and types
applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> TypeSource
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 -> TypeSource
Determines the type resulting from applying an expression to a function with the given type
dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])Source