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[Bug tree-optimization/61559] FAIL: gcc.dg/builtin-bswap-8.c on i686 with -mmovbe
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 04 Sep 2014 09:52:06 +0000
- Subject: [Bug tree-optimization/61559] FAIL: gcc.dg/builtin-bswap-8.c on i686 with -mmovbe
- Auto-submitted: auto-generated
- References: <bug-61559-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61559
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Aren't these optimizations actually a pessimization for -mmovbe if the inner
bswap is on a read from memory? Assuming the load and bswap instruction is
cheap, then e.g. loading two values with bswap on them and doing say xor on
them afterwards might be cheaper than load the two values, xor them and then
bswap them (because for that bswap you don't have a load+bswap instruction).