[Bug tree-optimization/79690] New: Vectorizer drops gs: prefix

[me at manueljacob dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79690

            Bug ID: 79690
           Summary: Vectorizer drops gs: prefix
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: me at manueljacob dot de
                CC: jakub at gcc dot gnu.org, rguenth at gcc dot gnu.org
  Target Milestone: ---

void fill(unsigned char __seg_gs *arr, unsigned char c, long n) {
    for (long i = 0; i < n; ++i)
        arr[i] = c;
}

On x86-64, gcc -O3 emits this instruction, missing the gs: prefix:

movaps  %xmm0, -16(%rcx)