#5400: GHC loops on compiling with optimizations -------------------------------------+------------------------------------- Reporter: noschinl | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 7.0.4 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgraf): Note that the reproduction lacks a `{-# LANGUAGE ConstrainedClassMethods #-}` to compile with GHC 8.2.1 and then compiles flawlessly with -O2. The typical Russel's paradox example from the user's guide just crashes with a panic (similar to #5448): {{{ ghc.exe: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-mingw32): Simplifier ticks exhausted When trying UnfoldingDone russel 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: 6361 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 }}} I'd advocate this to be a warning rather than a panic, but otherwise consider the whole issue fixed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5400#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler