[Bug tree-optimization/79723] New: Another case of dropped gs: prefix

[me at manueljacob dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79723

            Bug ID: 79723
           Summary: Another case of dropped gs: prefix
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: me at manueljacob dot de
                CC: rguenth at gcc dot gnu.org
  Target Milestone: ---

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

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

movaps  %xmm0, -16(%rdx)

It works when replacing "unsigned char *" with "long", even though they have
the same size and alignment.