[Bug tree-optimization/77605] [5/6/7 Regression] wrong code at -O3 on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77605

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.2.4
   Target Milestone|---                         |5.5
            Summary|wrong code at -O3 on        |[5/6/7 Regression] wrong
                   |x86_64-linux-gnu            |code at -O3 on
                   |                            |x86_64-linux-gnu
      Known to fail|                            |4.3.6, 4.5.4

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Non-surprisingly found a working version.  This is outer loop vectorization at
play and it looks like a dependence analysis issue to me:

  <bb 3>:
  # a.1_26 = PHI <0(2), _14(7)>
  # ivtmp_32 = PHI <8(2), ivtmp_7(7)>

  <bb 4>:
  # b.0_27 = PHI <0(3), _12(5)>
  # ivtmp_34 = PHI <2(3), ivtmp_33(5)>
  _8 = b.0_27 + 6;
  _9 = c[b.0_27][_8];
  _10 = _9 ^ 1;
  c[b.0_27][a.1_26] = _10;
  _12 = b.0_27 + 1;
  ivtmp_33 = ivtmp_34 - 1;
  if (ivtmp_33 != 0)
    goto <bb 5>;
  else
    goto <bb 6>;

  <bb 5>:
  goto <bb 4>;

  <bb 6>:
  _14 = a.1_26 + 1;
  ivtmp_7 = ivtmp_32 - 1;
  if (ivtmp_7 != 0)
    goto <bb 7>;
  else
    goto <bb 8>;

  <bb 7>:
  goto <bb 3>;

(compute_affine_dependence
  stmt_a: _9 = c[b.0_27][_8];
  stmt_b: c[b.0_27][a.1_26] = _10;
(analyze_overlapping_iterations
  (chrec_a = {6, +, 1}_2)
  (chrec_b = {0, +, 1}_1)
(analyze_miv_subscript
(analyze_subscript_affine_affine
  (overlaps_a = no dependence)
  (overlaps_b = no dependence))
)
  (overlap_iterations_a = no dependence)
  (overlap_iterations_b = no dependence))
) -> no dependence