#14208: Performance with -O2 is worse than with -O0 which is worse than runghc -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In this particular case `-O2` is 2x slower than `-O0` and `-O0` is 2x slower than `runghc`. Please see the github repo: https://github.com /harendra-kumar/ghc-perf to reproduce the issue. Readme file in the repo has instructions to reproduce. The issue seems to occur when the code is placed in a different module. When all the code is in the same module the problem does not occur. In that case `-O2` is faster than `-O0`. However, when the code is split into two modules the performance gets inverted. Also, it does not occur always, when I tried to change the code to make it simpler for repro the problem did not occur. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14208 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler