[llvm-bugs] [Bug 35601] New: Missed optimization in math expression: sqrt(pow(a, 2.0)) == a

via llvm-bugs llvm-bugs at lists.llvm.org
Sun Dec 10 07:20:20 PST 2017


            Bug ID: 35601
           Summary: Missed optimization in math expression: sqrt(pow(a,
                    2.0)) == a
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs 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

#include <cmath>

double test(double a, double b, double c, double d)
    return sqrt(pow(a, 2.0));

generates this assembly:

test(double, double, double, double): # @test(double, double, double, double)
  vmulsd xmm0, xmm0, xmm0
  vsqrtsd xmm0, xmm0, xmm0

gcc(trunk) with '--std=c++17 -O3 -march=native -ffast-math' flags generates

test(double, double, double, double):
        vandpd  xmm0, xmm0, XMMWORD PTR .LC0[rip]
        .long   4294967295
        .long   2147483647
        .long   0
        .long   0

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