#9718: Avoid TidyPgm predicting what CorePrep will do -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: CodeGen, CAFs Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Re "Finally I see" Simon M pointed out the that the code generator has a special case for indirection bindings `f = g`: {{{ cgTopRhsClosure dflags rec id ccs upd_flag args body = ... where -- special case for a indirection (f = g). We create an IND_STATIC -- closure pointing directly to the indirectee. This is exactly -- what the CAF will eventually evaluate to anyway, we're just -- shortcutting the whole process, and generating a lot less code -- (#7308) -- -- Note: we omit the optimisation when this binding is part of a -- recursive group, because the optimisation would inhibit the black -- hole detection from working in that case. Test -- concurrent/should_run/4030 fails, for instance. -- gen_code dflags _ closure_label | StgApp f [] <- body, null args, isNonRec rec = ... }}} We decided that: * The code generator makes an IND_STATIC for these * So `f` itself is not a CAF * But it might still be CAFFY if `g` is. Hence the CAF analysis could (and probably should) take advantage of this special case (alas, still a form of prediction!) provided it points to a specific Note about it in the code generator. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9718#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler