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[Bug middle-end/50168] __builtin_ctz() and intrinsics __bsr(), __bsf() generate suboptimal code on x86_64
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 24 Aug 2011 09:40:44 +0000
- Subject: [Bug middle-end/50168] __builtin_ctz() and intrinsics __bsr(), __bsf() generate suboptimal code on x86_64
- Auto-submitted: auto-generated
- References: <bug-50168-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50168
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011-08-24
Ever Confirmed|0 |1
--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-24 09:40:44 UTC ---
Hm, so the best thing we can do is a peephole recognizing that
10: 48 0f bc ff bsf %rdi,%rdi
14: 48 63 ff movslq %edi,%rdi
when rdi is zero it will stay so and the movslq is redundant?