#15703: Significant compilation time blowup when refactoring singletons-heavy code -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.8.1 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #15725 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): After some digging, I've found the commit that made compiling this program become so much faster. It's commit 55a3f8552c9dc9b84e204ec6623c698912795347 (`Refactor coercion rule`). In the commit prior, it took this long to build: {{{ $ time ~/Software/ghc2/inplace/bin/ghc-stage2 -O1 -fforce-recomp Lib.hs [1 of 2] Compiling Lib2 ( Lib2.hs, Lib2.o ) [2 of 2] Compiling Lib ( Lib.hs, Lib.o ) real 3m17.647s user 3m17.776s sys 0m0.168s }}} But if I apply that commit, it then takes this long to build: {{{ $ time ~/Software/ghc2/inplace/bin/ghc-stage2 -O1 -fforce-recomp Lib.hs [1 of 2] Compiling Lib2 ( Lib2.hs, Lib2.o ) [2 of 2] Compiling Lib ( Lib.hs, Lib.o ) real 0m26.102s user 0m26.032s sys 0m0.108s }}} This is quite a humorous coincidence, since up to this point I had been under the impression that that commit had made compilation performance slightly //worse// overall. But this shows I was completely wrong! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15703#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler