#14688: Note [Lone variables] leads to missing a case-of-case opportunity -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Huh. I really don't think case-expressions should be expandable. I think that's an unintentional consequences of sharing `exprIsCheapX`. This patch makes both `foo` and `foo2` behave well. Would you like to do a full nofib run? {{{ diff --git a/compiler/coreSyn/CoreArity.hs b/compiler/coreSyn/CoreArity.hs index 945cad6..538648d 100644 --- a/compiler/coreSyn/CoreArity.hs +++ b/compiler/coreSyn/CoreArity.hs @@ -514,9 +514,9 @@ getBotArity _ = Nothing mk_cheap_fn :: DynFlags -> CheapAppFun -> CheapFun mk_cheap_fn dflags cheap_app | not (gopt Opt_DictsCheap dflags) - = \e _ -> exprIsCheapX cheap_app e + = \e _ -> exprIsCheapX True cheap_app e | otherwise - = \e mb_ty -> exprIsCheapX cheap_app e + = \e mb_ty -> exprIsCheapX True cheap_app e || case mb_ty of Nothing -> False Just ty -> isDictLikeTy ty diff --git a/compiler/coreSyn/CoreUnfold.hs b/compiler/coreSyn/CoreUnfold.hs index c459fd2..f30aca6 100644 --- a/compiler/coreSyn/CoreUnfold.hs +++ b/compiler/coreSyn/CoreUnfold.hs @@ -1241,8 +1241,8 @@ tryUnfolding dflags id lone_variable = True | otherwise = case cont_info of - CaseCtxt -> not (lone_variable && is_wf) -- Note [Lone variables] - ValAppCtxt -> True -- Note [Cast then apply] + CaseCtxt -> not (lone_variable && is_exp) -- Note [Lone variables] + ValAppCtxt -> True -- Note [Cast then apply] RuleArgCtxt -> uf_arity > 0 -- See Note [Unfold info lazy contexts] DiscArgCtxt -> uf_arity > 0 -- RhsCtxt -> uf_arity > 0 -- diff --git a/compiler/coreSyn/CoreUtils.hs b/compiler/coreSyn/CoreUtils.hs index 5e32dc6..c99e05f 100644 --- a/compiler/coreSyn/CoreUtils.hs +++ b/compiler/coreSyn/CoreUtils.hs @@ -1131,18 +1131,18 @@ in this (which it previously was): -} -------------------- +exprIsWorkFree :: CoreExpr -> Bool -- See Note [exprIsWorkFree] +exprIsWorkFree = exprIsCheapX True isWorkFreeApp + exprIsCheap :: CoreExpr -> Bool -exprIsCheap = exprIsCheapX isCheapApp +exprIsCheap = exprIsCheapX True isCheapApp exprIsExpandable :: CoreExpr -> Bool -- See Note [exprIsExpandable] -exprIsExpandable = exprIsCheapX isExpandableApp - -exprIsWorkFree :: CoreExpr -> Bool -- See Note [exprIsWorkFree] -exprIsWorkFree = exprIsCheapX isWorkFreeApp +exprIsExpandable = exprIsCheapX False isExpandableApp -------------------- -exprIsCheapX :: CheapAppFun -> CoreExpr -> Bool -exprIsCheapX ok_app e +exprIsCheapX :: Bool -> CheapAppFun -> CoreExpr -> Bool +exprIsCheapX ok_case ok_app e = ok e where ok e = go 0 e @@ -1153,7 +1153,8 @@ exprIsCheapX ok_app e go _ (Type {}) = True go _ (Coercion {}) = True go n (Cast e _) = go n e - go n (Case scrut _ _ alts) = ok scrut && + go n (Case scrut _ _ alts) = ok_case && + ok scrut && and [ go n rhs | (_,_,rhs) <- alts ] go n (Tick t e) | tickishCounts t = False | otherwise = go n e }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14688#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler