[Bug target/95814] New: Failure to optimize __builtin_ia32_rsqrtss properly

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95814

            Bug ID: 95814
           Summary: Failure to optimize __builtin_ia32_rsqrtss properly
           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: ---

typedef float v4f32 __attribute__((vector_size(16)));

float f(float x)
{
    return __builtin_ia32_rsqrtss((v4f32){x, 0, 0, 0})[0];
}

With -O3, LLVM outputs this :

f(float):
  rsqrtss xmm0, xmm0
  ret

GCC outputs this :

f(float):
  pxor xmm1, xmm1
  movss xmm1, xmm0
  movaps xmm0, xmm1
  rsqrtss xmm0, xmm1
  ret