#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): Now that we have implemented the fix as outlined in D4395, it turns out that while the change is desirable overall, it does not actually improve performance significantly; `simplCast` still appears at the top of the profile, as evidenced here: {{{ Mon Mar 26 15:24 2018 Time and Allocation Profiling Report (Final) ghc-stage2 +RTS -p -RTS -B/home/tobias/well- typed/devel/ghc/D4395-modified/inplace/lib ./cases/Grammar.hs -o ./a -fforce-recomp total time = 19.66 secs (19655 ticks @ 1000 us, 1 processor) total alloc = 24,638,084,488 bytes (excludes profiling overheads) COST CENTRE MODULE SRC %time %alloc simplCast Simplify compiler/simplCore/Simplify.hs:(1213,5)-(1215,37) 73.8 76.0 tc_rn_src_decls TcRnDriver compiler/typecheck/TcRnDriver.hs:(494,4)-(556,7) 8.3 8.4 CoreTidy HscMain compiler/main/HscMain.hs:1253:27-67 2.8 2.2 SimplTopBinds SimplCore compiler/simplCore/SimplCore.hs:770:39-74 2.7 1.9 coercionKind Coercion compiler/types/Coercion.hs:1698:3-7 1.8 3.4 zonkTopDecls TcRnDriver compiler/typecheck/TcRnDriver.hs:(445,16)-(446,43) 1.3 1.3 deSugar HscMain compiler/main/HscMain.hs:511:7-44 1.1 0.8 }}} We clearly shouldn't be spending 15 seconds in `simplCast`, so more digging is required. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14737#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler