[Bug middle-end/126418] New: PR113894 introduces new UB in optimized code

[kristerw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126418

            Bug ID: 126418
           Summary: PR113894 introduces new UB in optimized code
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
            Blocks: 118443
  Target Milestone: ---

The function below does not invoke undefined behavior when called as:
  f_cmp_gt_commuted(0x80000000, 0);

int f_cmp_gt_commuted(int x, int y)
{
  int cmp = x > y;
  return cmp + (-cmp ^ x);
}

But compiling this for x86_64 with -O1 makes forwprop1 transform it into the
GIMPLE below, where the computation of _9 invokes undefined behavior:

int f_cmp_gt_commuted (int x, int y)
{
  int cmp;
  bool _1;
  int _7;
  int _9;

  <bb 2> :
  _1 = x_4(D) > y_5(D);
  _9 = -x_4(D);
  _7 = _1 ? _9 : x_4(D);
  return _7;
}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118443
[Bug 118443] [Meta bug] Bugs triggered by and blocking more smtgcc testing