[Bug middle-end/50168] __builtin_ctz() and intrinsics __bsr(), __bsf() generate suboptimal code on x86_64

[rguenth at gcc dot gnu.org]

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?