[Bug tree-optimization/83351] New: Missed optimization in math expression: sin^2(a) + cos^2(a) == 1

[zamazan4ik at tut dot by]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83351

            Bug ID: 83351
           Summary: Missed optimization in math expression: sin^2(a) +
                    cos^2(a) == 1
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zamazan4ik at tut dot by
  Target Milestone: ---

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


#include <cmath>

double test(double a)
{
    return cos(a) * cos(a) + sin(a) * sin(a);
}


generates this assembly:


test(double):
        sub     rsp, 24
        mov     rsi, rsp
        lea     rdi, [rsp+8]
        call    sincos
        vmovsd  xmm1, QWORD PTR [rsp+8]
        vmovsd  xmm0, QWORD PTR [rsp]
        add     rsp, 24
        vmulsd  xmm1, xmm1, xmm1
        vfmadd132sd     xmm0, xmm1, xmm0
        ret


But there is formula: sin^2(a) + cos^2(a) == 1. And it can be compiled in
faster way.