[Bug tree-optimization/118922] [13/14/15 regression] Miscompile at -O2/3 since r13-6945-g429a7a88438cc8

[amacleod at redhat dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118922

--- Comment #12 from Andrew Macleod <amacleod at redhat dot com> ---
Hmm.  Going into phiopt2, I see:

  <bb 5> [local count: 1014686024]:
  if (h_6 != 0)
    goto <bb 7>; [94.50%]
  else
    goto <bb 6>; [5.50%]

  <bb 6> [local count: 114863530]:
  # h_6 = PHI <0(4), 1(5)>

  <bb 7> [local count: 1073741824]:
  # f_8 = PHI <0(5), h_6(6)>
  _9 = f_8 ^ 1;
  a.0_10 = a;
  _11 = _9 + a.0_10;
  if (_11 != -117)
    goto <bb 5>; [94.50%]
  else
    goto <bb 8>; [5.50%]


and PHIOPT2 says:

COND_EXPR in block 5 and PHI in block 7 converted to straightline code.
Merging blocks 4 and 6
Removing basic block 5

and produces:

  <bb 4> [local count: 59055799]:
  c = d_3;

  <bb 5> [local count: 1073741824]:
  # f_8 = PHI <0(5), 0(4)>
  _9 = f_8 ^ 1;
  a.0_10 = a;
  _11 = _9 + a.0_10;
  if (_11 != -117)
    goto <bb 5>; [94.50%]
  else
    goto <bb 6>; [5.50%]

It seems to have  lost the possibility of h_6 being 1 or 0, and it looks like
it is now an infinite loop.