#10007: Fix misattribution of Cost Centre profiles to lintAnnots -------------------------------------+------------------------------------- Reporter: thoughtpolice | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Profiling | Version: 7.10.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: #9961 | Differential Revisions: Phab:D616 | Phab:D636 -------------------------------------+------------------------------------- Comment (by scpmw): Yes - I investigated this again a month ago, and found that SM's fix didn't correct the whole problem. In fact, if I remember correctly what we end up with is something like {{{ case scctick<SpecConstr> specConstrProgram of ... }}} In this situation the tick will fail to actually capture any cost in `specConstrProgram`, which will instead end up in the cost-centre next in the hierarchy, which happens to be `lintAnnots` (`Core2Core` before). As explained in D616 and #5654, this is a fairly fundamental problem: GHC simply doesn't implement the cost-centre semantics for function values correctly. Correcting this isn't exactly easy - I have been experimenting in the past weeks, and the best solution I can come up with (still?) involves a new closure type that wraps function values when they escape cost-centre scopes. Two possible solutions here: We could attempt another stopgap measure. For example, the above code should probably in-line as it is only used once. Building the full solution will still need a bit more tinkering, but I might be able to make a proposal soon-ish (... just need to get it to stop crashing. Seems getting register saving right can be surprisingly tricky). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10007#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler