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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2013-12-11 18:30:54 +0000 |
|---|---|---|
| committer | Joachim Breitner <mail@joachim-breitner.de> | 2013-12-12 11:26:58 +0000 |
| commit | ba78bf1772c9d695a0ded932eeceed10622d91a4 (patch) | |
| tree | 0d49084ecec0f2938348a57c3758fc86c9489af6 | |
| parent | 838da6fc74266cf6e561d6ba0cb1c8bd052b4efc (diff) | |
| download | haskell-ba78bf1772c9d695a0ded932eeceed10622d91a4.tar.gz | |
Do not split void functions
This is authored by SPJ, and split out out "Improve the handling of
used-once stuff" by Joachim.
| -rw-r--r-- | compiler/stranal/WorkWrap.lhs | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/compiler/stranal/WorkWrap.lhs b/compiler/stranal/WorkWrap.lhs index b66a449119..14a01d5097 100644 --- a/compiler/stranal/WorkWrap.lhs +++ b/compiler/stranal/WorkWrap.lhs @@ -17,6 +17,7 @@ import CoreSyn import CoreUnfold ( certainlyWillInline, mkInlineUnfolding, mkWwInlineRule ) import CoreUtils ( exprType, exprIsHNF ) import CoreArity ( exprArity ) +import Type ( isVoidTy ) import Var import Id import IdInfo @@ -256,7 +257,7 @@ tryWW dflags is_rec fn_id rhs -- Furthermore, don't even expose strictness info = return [ (fn_id, rhs) ] - | is_fun && (any worthSplittingArgDmd wrap_dmds || returnsCPR res_info) + | is_fun && (worth_splitting_args wrap_dmds rhs || returnsCPR res_info) = checkSize dflags new_fn_id rhs $ splitFun dflags new_fn_id fn_info wrap_dmds res_info rhs @@ -274,7 +275,13 @@ tryWW dflags is_rec fn_id rhs fn_dmd = demandInfo fn_info inline_act = inlinePragmaActivation (inlinePragInfo fn_info) - -- In practice it always will have a strictness + worth_splitting_args [d] (Lam b _) + | isAbsDmd d && isVoidTy (idType b) + = False -- Note [Do not split void functions] + worth_splitting_args wrap_dmds _ + = any worthSplittingArgDmd wrap_dmds + + -- In practice it always will have a strictness -- signature, even if it's a uninformative one strict_sig = strictnessInfo fn_info StrictSig (DmdType env wrap_dmds res_info) = strict_sig @@ -394,6 +401,17 @@ noOneShotInfo :: [Bool] noOneShotInfo = repeat False \end{code} +Note [Do not split void functions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this rather common form of binding: + $j = \x:Void# -> ...no use of x... + +Since x is not used it'll be marked as absent. But there is no point +in w/w-ing because we'll simply add (\y:Void#), see WwLib.mkWorerArgs. + +If x has a more interesting type (eg Int, or Int#), there *is* a point +in w/w so that we don't pass the argument at all. + Note [Thunk splitting] ~~~~~~~~~~~~~~~~~~~~~~ Suppose x is used strictly (never mind whether it has the CPR |