#15445: SPECIALIZE one of two identical functions does not fire well -------------------------------------+------------------------------------- Reporter: nobrakal | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: None/Unknown | Test Case: | simplCore/should_compile/T15445 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"3addf72a6f40747cff213653382eb4476bdb53da/ghc" 3addf72/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="3addf72a6f40747cff213653382eb4476bdb53da" Preserve specialisations despite CSE Trac #15445 showed that, as a result of CSE, a function with an automatically generated specialisation RULE could be inlined before the RULE had a chance to fire. This patch attaches a NOINLINE[2] activation to the Id, during CSE, to stop this happening. See Note [Delay inlining after CSE] ---- Historical note --- This patch is simpler and more direct than an earlier version: commit 2110738b280543698407924a16ac92b6d804dc36 Author: Simon Peyton Jones <simonpj@microsoft.com> Date: Mon Jul 30 13:43:56 2018 +0100 Don't inline functions with RULES too early We had to revert this patch because it made GHC itself slower. Why? It delayed inlining of /all/ functions with RULES, and that was very bad in TcFlatten.flatten_ty_con_app * It delayed inlining of liftM * That delayed the unravelling of the recursion in some dictionary bindings. * That delayed some eta expansion, leaving flatten_ty_con_app = \x y. let <stuff> in \z. blah * That allowed the float-out pass to put sguff between the \y and \z. * And that permanently stopped eta expasion of the function, even once <stuff> was simplified. -- End of historical note --- }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15445#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler