#12915: cmmImplementSwitchPlans creates duplicate blocks -------------------------------------+------------------------------------- Reporter: alexbiehl | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 michalt): @nomeata: Yes, we definitely don't want to move the sinking pass before stack layout. Stack layout can generate a lot of unnecessary stuff that the sinking pass removes. There's also a `Node [Sinking after stack layout]` that explains why we don't currently run sinking twice (before and after stack layout). As for the comment in code: {{{ -- Any work storing block Labels must be performed _after_ -- elimCommonBlocks }}} IIUC it refers to things like proc point analysis that stores the labels for later use (and since `elimCommonBlock` can remove blocks/labels, it might no longer be safe to use those results). Anyway, I did a quick experiment and modified `CmmPipeline`: - Added a call to `elimCommonBlocks` directly after the sinking pass. - Duplicated the proc point analysis so that the actual splitting uses up to date information. Results: - Binary size: {{{ -1 s.d. ----- -1.0% +1 s.d. ----- -0.8% Average ----- -0.9% }}} - Module sizes: {{{ -1 s.d. ----- -1.8% +1 s.d. ----- +0.6% Average ----- -0.6% }}} - Compile times: {{{ -1 s.d. ----- -1.6% +1 s.d. ----- +3.3% Average ----- +0.8% }}} - Compiler allocations: {{{ -1 s.d. ----- +0.3% +1 s.d. ----- +1.0% Average ----- +0.7% }}} Runtime didn't seem to change (there were some outliers in the 1-2% area, but I think that's just noise). So it seems that there is actually some potential to decrease binary size, but I'm not sure it's worth the compile time overhead. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12915#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler