#14737: Improve performance of Simplify.simplCast -------------------------------------+------------------------------------- Reporter: tdammers | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #11735 #14683 | Differential Rev(s): Phab:D4385 Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers):
However, that may still leave simplCast at the top... does it? If it was taking 78% of 20sec before, that's 16 sec. So reducing that to near-zero (which it should be) would take use to 5s, not 12s.
Correct; `isReflexiveCo` accounted for about half the execution time spent in `simplCast`. With this change, `isReflexiveCo` drops to 1.1% of overall execution time, and `simplCast` to about 61%. So this is a big improvement, but we're not done yet. The remaining main culprit is `pushCoTyArg`.
What happens if you leave out the call to isReflexiveCo altogether? It'll get done in the next round anyway, by optCoercion.
I'll try that, but considering that `isReflexiveCo` is no longer critical, I don't expect it to make much of a difference. For reference, here's the current profiler output: {{{ Wed Mar 28 20:44 2018 Time and Allocation Profiling Report (Final) ghc-stage2 +RTS -p -RTS -B/home/tobias/well- typed/devel/ghc/T14737/inplace/lib ./cases/Grammar.hs -o ./a -fforce- recomp total time = 12.35 secs (12354 ticks @ 1000 us, 1 processor) total alloc = 14,410,284,936 bytes (excludes profiling overheads) COST CENTRE MODULE SRC %time %alloc pushCoTyArg Simplify compiler/simplCore/Simplify.hs:1229:63-83 54.6 55.5 tc_rn_src_decls TcRnDriver compiler/typecheck/TcRnDriver.hs:(494,4)-(556,7) 13.1 14.3 CoreTidy HscMain compiler/main/HscMain.hs:1253:27-67 4.8 3.9 SimplTopBinds SimplCore compiler/simplCore/SimplCore.hs:770:39-74 4.2 3.2 coercionKind Coercion compiler/types/Coercion.hs:1701:3-7 2.8 6.0 simplCast Simplify compiler/simplCore/Simplify.hs:(1213,5)-(1215,37) 2.5 2.5 zonkTopDecls TcRnDriver compiler/typecheck/TcRnDriver.hs:(445,16)-(446,43) 2.3 2.2 deSugar HscMain compiler/main/HscMain.hs:511:7-44 1.5 1.3 isReflexiveCo Simplify compiler/simplCore/Simplify.hs:1260:40-55 1.1 1.0 Parser HscMain compiler/main/HscMain.hs:(316,5)-(384,20) 1.1 1.6 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14737#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler