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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/98647] New: Failure to optimize out convertion from
 float to vector type
Date: Wed, 13 Jan 2021 00:57:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98647

            Bug ID: 98647
           Summary: Failure to optimize out convertion from float to
                    vector type
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

float f(float val)
{
    return _mm_cvtss_f32(_mm_and_ps(_mm_set_ss(val),
_mm_castsi128_ps(_mm_set1_epi32(0x7fffffff))));
}

This can be optimized to avoid the conversions in the emitted assembly code.
This optimization is done by LLVM, but not by GCC.

LLVM code generation :

.LCPI1_0:
  .long 0x7fffffff # float NaN
  .long 0x7fffffff # float NaN
  .long 0x7fffffff # float NaN
  .long 0x7fffffff # float NaN
f(float): # @f(float)
  andps xmm0, xmmword ptr [rip + .LCPI1_0]
  ret

GCC code generation :

f(float):
  pxor xmm1, xmm1
  movss xmm1, xmm0
  movaps xmm0, XMMWORD PTR .LC1[rip]
  andps xmm0, xmm1
  ret

.LC1:
  .long 2147483647
  .long 2147483647
  .long 2147483647
  .long 2147483647=