[Bug tree-optimization/101445] [11/12 Regression] wrong code at -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101445

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Simplified testcase, fails at -O2 -ftree-loop-vectorize

int a[35] = {1, 1, 3};
void __attribute__((noipa))
foo ()
{
  for (int b = 4; b >= 0; b--)
    { 
      int tem = a[b * 5 + 3 + 1];
      a[b * 5 + 3] = tem;
      a[b * 5 + 2] = tem;
      a[b * 5 + 1] = tem;
      a[b * 5 + 0] = tem;
    }
}
int main()
{
  foo ();
  for (int d = 0; d < 25; d++)
    if (a[d] != 0)
      __builtin_abort ();
  return 0;
}

the load is vectorized in an odd way, but "correct" - but the final IV
update(s)
are bogus.

  <bb 2>
  vectp_a.7_34 = &a + 84;  // &a[21]

  <bb 3>
  # vectp_a.6_35 = PHI <vectp_a.6_36(5), vectp_a.7_34(2)>
...
  vect_tem_9.8_37 = MEM <vector(4) int> [(int *)vectp_a.6_35];
  vect_tem_9.9_38 = VEC_PERM_EXPR <vect_tem_9.8_37, vect_tem_9.8_37, { 3, 2, 1,
0 }>;
  vectp_a.6_39 = vectp_a.6_35 + 18446744073709551600;  // -16
  vect_tem_9.10_40 = MEM <vector(4) int> [(int *)vectp_a.6_39];
  vect_tem_9.11_41 = VEC_PERM_EXPR <vect_tem_9.10_40, vect_tem_9.10_40, { 3, 2,
1, 0 }>;
  vectp_a.6_42 = vectp_a.6_39 + 18446744073709551604;  // -12
  vect_tem_9.12_43 = VEC_PERM_EXPR <vect_tem_9.9_38, vect_tem_9.9_38, { 0, 0,
0, 0 }>;
...
  vectp_a.6_36 = vectp_a.6_42 + 18446744073709551600;  // -16

we're doing VMAT_CONTIGUOUS_REVERSE but the group has gaps and we fail to
account for the reverse when computing group_gap_adj (which should have been
+12, not -12).