#5448: GHC stuck in infinite loop compiling with optimizations -------------------------------------+------------------------------------- Reporter: ronwalf | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 7.0.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgraf): Actually, this doesn't reproduce anymore, at least not in the way described. For GHC 8.2.1, the original ghcloop.hs elicits the following panic: {{{ ghc.exe: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-mingw32): Simplifier ticks exhausted When trying RuleFired Class op funcEq To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 15160 Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler\utils\Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler\utils\Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler\simplCore\SimplMonad.hs:199:31 in ghc:SimplMonad }}} That's better than looping forever, although I don't know why it's a panic rather than a warning. Note that it also includes which function was the culprit. I read somewhere that the Simplifier adopted its fuel-based approach in the meantime, which may be the reason this is 'fixed'. The contravariant example doesn't reproduce at all. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5448#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler