[Bug tree-optimization/87621] New: auto-vectorization fails for exponentiation code

[hoganmeier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87621

            Bug ID: 87621
           Summary: auto-vectorization fails for exponentiation code
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hoganmeier at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/bgieBT

template <typename T>
T pow(T x, unsigned int n)
{
        if (!n)
                return 1;

        T y = 1;
        while (n > 1)
        {
                if (n%2)
                        y *= x;
                x = x*x; // unsupported use in stmt
                n /= 2;
        }
        return x*y;
}

void testVec(int* x)
{
        // loop nest containing two or more consecutive inner loops cannot be
vectorized
        for (int i = 0; i < 8; ++i)
                x[i] = pow(x[i], 10);
}