#12996: Memory leak in recursion when switching from -O1 to -O2 -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: Memory leak, | Operating System: Unknown/Multiple optimization | Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- For example code see attachment. When compiling with -O1 the code behaves as expected with each loop taking about the same amount of time. At -O2 each iteration takes (nonlinear) more time than the last and leaks memory. It gets slow enough that I never bothered to let it run past 40 iterations since the slowdown seems to be exponential. I initially hit the bug in code using a Set instead of list but turns out the issue can be reduced to an example with lists. Removing either filter, pattern matching or changing the loop fixes the issue. I tested it under the following conditions: * Compiler flags: -fno-full-laziness/No flags * Compiler versions: GHC 8.0.1 and 7.10.3e * Operating Systems: Windows 10, Linux Mint In every case -O1 works as expected with -O2 showing exponential slowdown with each iteration. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12996 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler