[Bug tree-optimization/126466] New: [17 Regression] popcount recognition doesn't validate one of the masks

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126466

            Bug ID: 126466
           Summary: [17 Regression] popcount recognition doesn't validate
                    one of the masks
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---

const unsigned m1 = 0x55555555UL;
const unsigned m2 = 0x33333333UL;
const unsigned m3 = 0x0F0F0F0FUL;
const unsigned m4 = 0x0000FFFFUL;

__attribute__((noipa)) unsigned
popc (unsigned x)
{
  x = x - ((x >> 1) & m1);
  x = x - 3 * ((x >> 2) & m2);
  x = (x + (x >> 4)) & m3;
  x = x + (x >> 8);
  x = x + (x >> 16);
  return x & m4;
}

int
main (void)
{
  /* The low half holds a population count of 13, the high half one of 9.  */
  if (popc (0x12345678u) != 0x090du)
    __builtin_abort ();
  return 0;
}

aborts at -O2, passes with GCC 16