#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):
Alternatively I think we could pass an environment of updated ids to topStgBindHasCafRefs and friends.
Yes, let's do something more like that. But I have forgotten how SRTs are constructed. We clearly need two passes: 1. Find out which top-level bindings are CAFFy: that is, refers (transitively) to a CAF. That simply involves a free-variable analysis and a fixpoint calculation. 2. Build an SRT for each closure that lists the CAFFy things it mentions. It's not obvious where that is done today -- can you point to it? For step (2) it occurs to me that we could decorate the `StgRhsClosure` with the list of things to put in its SRT, just as we decorate it with the list of locally-bound free variables to put in its closure. That seems so obvious, I'm not sure why we don't do that. One other thought. Suppose we have {{{ x = factorial 200 p = (x,True) q = (False,x) wubble = \x. (p,q) }}} Then `x`, `y` and `p` are all CAFFy, so currently `wurble`'s SRT will contain both `p` and `q`. But actually we need only one of them, because the goal is solely to keep `x` alive. So actually `wurble`'s SRT could list `p` alone, or `q` alone, or indeed just `x`. I'm not sure if this is worth exploiting; and doing so cross-module would mean we had to put more stuff in .hi files. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9718#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler