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From: "debiandev at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/62011] New: False Data Dependency in popcnt instruction Date: Mon, 04 Aug 2014 14:29:00 -0000 [thread overview] Message-ID: <bug-62011-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011 Bug ID: 62011 Summary: False Data Dependency in popcnt instruction Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: debiandev at gmail dot com On Sandy/Ivy Bridge and Haswell processors, the instruction: popcnt src, dest appears to have a false dependency on the destination register dest. Even though the instruction only writes to it, the instruction will wait until dest is ready before executing. This causes a loss in performance as explained here: http://stackoverflow.com/questions/25078285/replacing-a-32-bit-loop-count-variable-with-64-bit-introduces-crazy-performance
next reply other threads:[~2014-08-04 14:29 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-08-04 14:29 debiandev at gmail dot com [this message] 2014-08-05 9:07 ` [Bug target/62011] " rguenth at gcc dot gnu.org 2014-08-05 11:49 ` amonakov at gcc dot gnu.org 2014-08-05 13:40 ` debiandev at gmail dot com 2014-08-07 9:22 ` finis at in dot tum.de 2014-08-11 14:37 ` ysrumyan at gmail dot com 2014-08-12 8:38 ` ysrumyan at gmail dot com 2014-08-12 10:49 ` finis at in dot tum.de 2014-08-12 11:26 ` ysrumyan at gmail dot com 2014-08-13 8:23 ` rguenth at gcc dot gnu.org 2014-08-21 18:04 ` uros at gcc dot gnu.org 2014-08-21 18:06 ` ubizjak at gmail dot com 2021-10-11 13:46 ` malincns at 163 dot com
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