[llvm-bugs] [Bug 44153] New: copysign(x, signbit(x) ? +1.f : -1.f) folding

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44153

            Bug ID: 44153
           Summary: copysign(x, signbit(x) ? +1.f : -1.f) folding
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Keywords: code-quality
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: nok.raven at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

There is a problem with replacing boost's changesign:

#include <boost/math/special_functions/sign.hpp>
float changesign_boost(float x) {
  return boost::math::changesign(x);
}

#include <cmath>
float changesign_std(float x) {
  bool isneg = std::signbit(x);
  return std::copysign(x, isneg ? +1.f : -1.f);
}

changesign_boost(float):
  xorps   xmm0, xmmword ptr [rip + .LCPI0_0]
  ret

changesign_std(float):
  movd    eax, xmm0
  xor     ecx, ecx
  test    eax, eax
  sets    cl
  pand    xmm0, xmmword ptr [rip + .LCPI1_0]
  movd    xmm1, dword ptr [4*rcx + .LCPI1_1]
  pand    xmm1, xmmword ptr [rip + .LCPI1_2]
  por     xmm0, xmm1
  ret

https://godbolt.org/z/AN2VfR

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