[llvm-bugs] [Bug 35593] New: Missed optimization in math expression: simplify calls std::pow functions

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35593

            Bug ID: 35593
           Summary: Missed optimization in math expression: simplify calls
                    std::pow functions
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: zamazan4ik at tut.by
                CC: llvm-bugs at lists.llvm.org

clang(trunk) with '--std=c++17 -O3 -march=native -ffast-math' flags for this
code:

#include <cmath>

double f(double a, double b, double c)
{
    return std::pow(a, b) * std::pow(a, c);
}

generates this assembly:


f(double, double, double): # @f(double, double, double)
  sub rsp, 24
  vmovsd qword ptr [rsp + 16], xmm2 # 8-byte Spill
  vmovsd qword ptr [rsp], xmm0 # 8-byte Spill
  call pow
  vmovsd qword ptr [rsp + 8], xmm0 # 8-byte Spill
  vmovsd xmm0, qword ptr [rsp] # 8-byte Reload
  vmovsd xmm1, qword ptr [rsp + 16] # 8-byte Reload
  call pow
  vmulsd xmm0, xmm0, qword ptr [rsp + 8] # 8-byte Folded Reload
  add rsp, 24
  ret


GCC (trunk) with '--std=c++17 -O3 -march=native -ffast-math' flags generates
more optimal code:


f(double, double, double):
        vaddsd  xmm1, xmm1, xmm2
        jmp     __pow_finite

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