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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/56118] New: No constant propagation in vector field assignment
Date: Sat, 26 Jan 2013 17:37:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56118

             Bug #: 56118
           Summary: No constant propagation in vector field assignment
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: glisse@gcc.gnu.org
            Target: x86_64-linux-gnu


Hello,

with this code:

#include <x86intrin.h>
__m128d f(){
  __m128d r={3,4};
  r[0]=1;
  r[1]=2;
  return r;
}

gcc sees the following and fails to optimize it:

  r = { 3.0e+0, 4.0e+0 };
  BIT_FIELD_REF <r, 64, 0> = 1.0e+0;
  BIT_FIELD_REF <r, 64, 64> = 2.0e+0;

Nothing fixes it at the RTL level either, so we end up with:

    movapd    .LC0(%rip), %xmm0
    movlpd    .LC1(%rip), %xmm0
    movhpd    .LC2(%rip), %xmm0