#14226: Common Block Elimination pass doesn't eliminate common blocks -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 (CodeGen) | Resolution: | Keywords: 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 bgamari): Well, because we have an extremely narrow definition of "common". Namely, to be the same two blocks must be syntactically identical, including local register names. I don't know how often this happens in practice, but I'd imagine not terribly often. I think the criterion that you would ideally want is equivalence up to alpha renaming of local registers; unfortunately this would likely be considerably more costly to check for. This makes me wonder whether we shouldn't just try to avoid duplicating the blocks to begin with (e.g. addressing #14222 earlier in the compilation pipeline). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14226#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler