Some Intel processors appear to have a false dependency on the destination of the popcnt instruction. This could lead to poor
#13725: Remove false dependency on the destination of the popcnt instruction -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): Phab:D3539 | Wiki Page: -------------------------------------+------------------------------------- fryguybob writes in Phab:D3539, performance. A simple way to prevent this is to clear the destination register immediately before the popcnt instruction. Currently I can't produce code from GHC where the source and destination registers are not the same (perhaps someone is interested in producing a test case that does). I'm putting this here in case anyone is interested in investigating further. I'm opening this ticket so I can bump the diff out of the review queue, in hopes that someone might some day pick it up. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13725 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler