[Bug tree-optimization/71921] New: missed vectorization optimization

[arjan at linux dot intel.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71921

            Bug ID: 71921
           Summary: missed vectorization optimization
           Product: gcc
           Version: 6.1.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arjan at linux dot intel.com
  Target Milestone: ---

program below does not auto-vectorize to use the x86 "maxps" instruction even
though gcc is smart enough to know there is a "maxss" instruction...


gcc -O3 -ftree-vectorize -fopt-info-vec -fopt-info-vec-missed -march=westmere
test.cpp -S -o test.S

does not show any use of maxps in test.S



#include <vector>

void relu(float * __restrict__ output, const float * __restrict__ input, int
size)
{
    int i;
    int s2;

    s2 = size / 4;
    for (i = 0; i < s2 * 4; i++) {
        float t;
        t = input[i];
        output[i] = std::max(t, float(0));
    }
}