diff options
Diffstat (limited to 'compiler/GHC/Core/Utils.hs')
| -rw-r--r-- | compiler/GHC/Core/Utils.hs | 59 |
1 files changed, 2 insertions, 57 deletions
diff --git a/compiler/GHC/Core/Utils.hs b/compiler/GHC/Core/Utils.hs index 30597dd8e5..57a1ccacc3 100644 --- a/compiler/GHC/Core/Utils.hs +++ b/compiler/GHC/Core/Utils.hs @@ -23,7 +23,7 @@ module GHC.Core.Utils ( -- * Properties of expressions exprType, coreAltType, coreAltsType, mkLamType, mkLamTypes, mkFunctionType, - exprIsDupable, exprIsTrivial, getIdFromTrivialExpr, exprIsDeadEnd, + exprIsDupable, exprIsTrivial, getIdFromTrivialExpr, getIdFromTrivialExpr_maybe, exprIsCheap, exprIsExpandable, exprIsCheapX, CheapAppFun, exprIsHNF, exprOkForSpeculation, exprOkForSideEffects, exprOkForSpecEval, @@ -1073,63 +1073,8 @@ getIdFromTrivialExpr_maybe e go (Var v) = Just v go _ = Nothing -{- -exprIsDeadEnd is a very cheap and cheerful function; it may return -False for bottoming expressions, but it never costs much to ask. See -also GHC.Core.Opt.Arity.exprBotStrictness_maybe, but that's a bit more -expensive. --} -exprIsDeadEnd :: CoreExpr -> Bool --- See Note [Bottoming expressions] -exprIsDeadEnd e - | isEmptyTy (exprType e) - = True - | otherwise - = go 0 e - where - go n (Var v) = isDeadEndAppSig (idDmdSig v) n - go n (App e a) | isTypeArg a = go n e - | otherwise = go (n+1) e - go n (Tick _ e) = go n e - go n (Cast e _) = go n e - go n (Let _ e) = go n e - go n (Lam v e) | isTyVar v = go n e - go _ (Case _ _ _ alts) = null alts - -- See Note [Empty case alternatives] in GHC.Core - go _ _ = False - -{- Note [Bottoming expressions] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -A bottoming expression is guaranteed to diverge, or raise an -exception. We can test for it in two different ways, and exprIsDeadEnd -checks for both of these situations: - -* Visibly-bottom computations. For example - (error Int "Hello") - is visibly bottom. The strictness analyser also finds out if - a function diverges or raises an exception, and puts that info - in its strictness signature. - -* Empty types. If a type is empty, its only inhabitant is bottom. - For example: - data T - f :: T -> Bool - f = \(x:t). case x of Bool {} - Since T has no data constructors, the case alternatives are of course - empty. However note that 'x' is not bound to a visibly-bottom value; - it's the *type* that tells us it's going to diverge. - -A GADT may also be empty even though it has constructors: - data T a where - T1 :: a -> T Bool - T2 :: T Int - ...(case (x::T Char) of {})... -Here (T Char) is uninhabited. A more realistic case is (Int ~ Bool), -which is likewise uninhabited. - - -************************************************************************ +{- ********************************************************************* * * exprIsDupable * * |