#13723: Recover gracefully from simplifier tick exhaustion -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1-rc2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently, we have just one tick limit. If the simplifier runs out of ticks, GHC simply gives up and exits. But that shouldn't ''really'' be necessary. In a more ideal world, we'd have two or even three tick limits for different kinds of transformations. For example, there are === Transformations that must be performed before `CorePrep` === I hope that we can give a hard upper bound on how many ticks we need to perform these for a given program size. If that limit is exceeded, then we should report a bug. === Transformations that always reduce program size === If a transformation always reduces program size, we can always perform it, even if we're otherwise out of ticks. This includes, at least, beta reduction without duplication. While `RULES` are generally wild, it should be safe to apply rules that reduce code size ''immediately''. For example, {{{#!hs foldr c n (build f) ==> f c n }}} is always fine. These transformations can share a tick limit with the mandatory transformations mentioned above. === Transformations that never increase program size === We can be generous with these, but need some limit. === Transformations that may increase program size === These need the harshest limit, of course, but probably not (much?) harsher than what we currently have. ---- The idea is that even if one tick limit is exceeded, the "higher priority" transformations can be allowed to continue anyway. Exceeding tick limits for most transformations would lead to a warning, rather than an error. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13723 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler