[Bug target/54531] New: vpermilpd(x, 2 or 10) is a move

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54531

             Bug #: 54531
           Summary: vpermilpd(x, 2 or 10) is a move
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: gli...@gcc.gnu.org
            Target: x86_64-linux-gnu


Hello,

it is quite easy to make gcc generate instructions that are equivalent to
moves, but gcc doesn't realize that. Simple examples include
_mm256_permute_pd(x,10) and _mm_permute_pd(x,2), but I also got it while trying
a patch that generated some vec_selects. I believe those instructions should be
optimized out.

#include <x86intrin.h>
__m256d f(__m256d x){
  return _mm256_permute_pd(x,2+8);
}

gcc -O3 -S -mavx
(with -mavx2 we get vpermpd(x,228) which is a similar issue)