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[Bug target/62011] False Data Dependency in popcnt instruction
- From: "amonakov at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 05 Aug 2014 11:49:01 +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
Alexander Monakov <amonakov at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |amonakov at gcc dot gnu.org
--- Comment #2 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
I think adjusting for scheduling won't help much: rather than making the
compiler aware of increased latency, you'd need that either the register
allocator avoids using a recently written hard register for popcnt (I'm not
aware of such capability), or as a stopgap measure the compiler can issue a
dependency-breaking instruction (xor %reg %reg) just before popcnt.