#15019: Fix performance regressions from #14737 -------------------------------------+------------------------------------- Reporter: tdammers | Owner: tdammers Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #14737 | Differential Rev(s): phab:D4568 Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): OK, sure. Just check out GHC HEAD, and apply this patch: {{{ diff --git a/compiler/coreSyn/CoreOpt.hs b/compiler/coreSyn/CoreOpt.hs index f1ff68d133..6ddab2c94e 100644 --- a/compiler/coreSyn/CoreOpt.hs +++ b/compiler/coreSyn/CoreOpt.hs @@ -958,10 +958,14 @@ pushCoTyArg :: CoercionR -> Type -> Maybe (Type, Maybe CoercionR) -- If the returned coercion is Nothing, then it would have been reflexive; -- it's faster not to compute it, though. pushCoTyArg co ty + | isReflCo co + = Just (ty, Nothing) + -- The following is inefficient - don't do `eqType` here, the coercion -- optimizer will take care of it. See Trac #14737. - -- -- | tyL `eqType` tyR - -- -- = Just (ty, Nothing) + | tyL `eqType` tyR + = pprTrace "eqType fired: " (ppr (co, tyL, tyR)) $ + Just (ty, Nothing) | isForAllTy tyL = ASSERT2( isForAllTy tyR, ppr co $$ ppr ty ) @@ -993,10 +997,15 @@ pushCoValArg :: CoercionR -> Maybe (Coercion, Maybe Coercion) -- If the second returned Coercion is actually Nothing, then no cast is necessary; -- the returned coercion would have been reflexive. pushCoValArg co + -- The "easy" case; this doesn't interest us. + | isReflCo co + = Just (mkRepReflCo arg, Nothing) + -- The following is inefficient - don't do `eqType` here, the coercion -- optimizer will take care of it. See Trac #14737. - -- -- | tyL `eqType` tyR - -- -- = Just (mkRepReflCo arg, Nothing) + | tyL `eqType` tyR + = pprTrace "eqType fired: " (ppr (co, tyL, tyR)) $ + Just (mkRepReflCo arg, Nothing) | isFunTy tyL , (co1, co2) <- decomposeFunCo Representational co }}} Build with the `validate` flavor, and then: {{{ ./inplace/bin/ghc-stage2 -O2 testsuite/tests/perf/compiler/T9020.hs -fforce-recomp }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15019#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler