[llvm-bugs] [Bug 39480] New: Failure to simplify -min(-a, a) => max(-a, a)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39480

            Bug ID: 39480
           Summary: Failure to simplify -min(-a, a) => max(-a, a)
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: filcab at gmail.com, llvm-bugs at lists.llvm.org,
                    spatel+llvm at rotateright.com, tilkax at gmail.com

#include <algorithm>
#include <x86intrin.h>

int min_neg_s32(int a)
{
    return -std::min(-a, a);
}

__m128i min_neg_v4s32(__m128i a) {
    return _mm_sub_epi32(_mm_setzero_si128(),
_mm_min_epi32(_mm_sub_epi32(_mm_setzero_si128(), a), a));
}

float min_neg_f32(float a)
{
    return -std::min(-a, a);
}

https://godbolt.org/z/h4zTcS

clang: 

_Z11min_neg_s32i: # @_Z11min_neg_s32i
  movl %edi, %eax
  negl %eax
  cmpl %edi, %eax
  cmovgl %edi, %eax
  negl %eax
  retq
_Z13min_neg_v4s32Dv2_x: # @_Z13min_neg_v4s32Dv2_x
  vpxor %xmm1, %xmm1, %xmm1
  vpsubd %xmm0, %xmm1, %xmm2
  vpminsd %xmm0, %xmm2, %xmm0
  vpsubd %xmm0, %xmm1, %xmm0
  retq
_Z11min_neg_f32f: # @_Z11min_neg_f32f
  vmovaps .LCPI2_0(%rip), %xmm1 # xmm1 = [-0,-0,-0,-0]
  vxorps %xmm1, %xmm0, %xmm2
  vminss %xmm2, %xmm0, %xmm0
  vxorps %xmm1, %xmm0, %xmm0
  retq

gcc manages the scalar cases (s32 is interesting....) but not the vector case:

_Z11min_neg_s32i:
  movl %edi, %eax
  cltd
  xorl %edx, %eax
  subl %edx, %eax
  ret
_Z13min_neg_v4s32Dv2_x:
  vpxor %xmm1, %xmm1, %xmm1
  vpsubd %xmm0, %xmm1, %xmm2
  vpminsd %xmm0, %xmm2, %xmm0
  vpsubd %xmm0, %xmm1, %xmm0
  ret
_Z11min_neg_f32f:
  vmovss %xmm0, %xmm0, %xmm1
  vxorps .LC0(%rip), %xmm0, %xmm0
  vmaxss %xmm1, %xmm0, %xmm0
  ret

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