#9509: No automatic specialization of inlinable imports in 7.8 -------------------------------------+------------------------------------- Reporter: dolio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nfrisby): I now have a theory. Based on some of the notes I've found in the source code, I'm concluding (/recalling!) that "unfoldings should only be simplified gently" and "gently implies no eta-expansion". Notably, {{{SimplUtils.updModeForStableUnfoldings}}} sets {{{sm_eta_expand = False}}}, and the simplifier invokes that before entering a stable unfolding or a rule. However, in this case, we're seeing eta-expansion in the unfolding! I believe that is due to [https://github.com/ghc/ghc/blob/876b00ba25a615423f48b0cf9d443a9fd5dbd6f4/com... this use] of {{{gopt Opt_DoLambdaEtaExpansion dflags}}} in {{{SimplUtils.mkLam}}} --- it's checking the {{{DynFlag}}} instead of checking the {{{sm_eta_expand}}} flag within the {{{SimplEnv}}} (which is not passed to {{{mkLam}}}). Parts of the simplifier, notably {{{simplLam}}}, call {{{mkLam}}}. I've made "the fix" locally, and it indeed fixes this ticket's example case. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9509#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler