#15754: Move free variable computation to after STG passes -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9718 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * related: => #9718 Comment: So, for #9718 I'm working on a large Stg refactoring that fixes this ticket too. I'll add the detailed refactoring plan in #9718. Basically the proposal is we do analyses as late as possible, and for free variables we do the analysis right before code generation. But if late lambda lifting uses this information then that's not going to work, we need to do it earlier, and then make sure (perhaps only in debug builds or with a flag) that late lambda lift correctly updates free variables of closures. Because lll (late lambda lift) will be the first pass that'll need the free variables I think we should compute it right before the pass. That means (depending on when we're running lll) some passes may not have the information. In that case perhaps it's better to remove the fvs list from the syntax, and pass it around in an environment. Alternatively we could keep it in the syntax, do the computation in CoreToStg, and run a sanity check after each pass to make sure the information remains correct. However this means that a pass that doesn't need the information, but incidentally updates it (we currently don't have such a pass) will have to deal with the fvs field. Not sure if this is a huge concern right now.. Any thoughts? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15754#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler