[Bug tree-optimization/115395] [15 regression] libarchive miscompiled with -O2 -march=znver2 -fno-vect-cost-model since r15-1006-gd93353e6423eca

["sjames at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115395

--- Comment #3 from Sam James <sjames at gcc dot gnu.org> ---
Tidied up a bit:
```
struct {
  long header_size;
  long start_offset;
  long end_offset;
} myrar_dbo[5] = {{0, 87, 6980}, {0, 7087, 13980}, {0, 14087, 0}};

int i;
long offset;

int main() {
  offset += myrar_dbo[0].start_offset;
  while (i < 2) {
    i++;
    offset += myrar_dbo[i].start_offset - myrar_dbo[i - 1].end_offset;
  }
  if (offset != 301)
    __builtin_abort();
}
```