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[Bug target/62011] False Data Dependency in popcnt instruction
- From: "finis at in dot tum.de" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 07 Aug 2014 09:22:11 +0000
- Subject: [Bug target/62011] False Data Dependency in popcnt instruction
- Auto-submitted: auto-generated
- References: <bug-62011-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011
--- Comment #5 from finis at in dot tum.de ---
Maybe there are a lot more instructions with such a false dependency. popcnt
may only be the tip of the ice berg. I don't think Intel only got this
operation wrong and all other SSE/AVX/... instructions are correct. I rather
think a group of operations is implemented like popcnt. The source code in the
linked SO question yields a good testbed for other operations as well: Simply
replace popcount by another intrinsic and check if the performance deviations
occur.