[Bug tree-optimization/116120] New: Wrong code for (a ? x : y) != (b ? x : y)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116120

            Bug ID: 116120
           Summary: Wrong code for (a ? x : y) != (b ? x : y)
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

GCC is miscompiling the functions in g++.dg/tree-ssa/pr111150.C, such as:

typedef int v4si __attribute((__vector_size__(4 * sizeof(int))));
v4si f1_(v4si a, v4si b, v4si c, v4si d, v4si e, v4si f) {
  v4si X = a == b ? e : f;
  v4si Y = c == d ? e : f;
  return (X != Y);
}

The reason is that PR111150 implemented match patterns of the form:

  (a ? x : y) != (b ? x : y) --> (a^b) ? TRUE  : FALSE

But this optimization is not correct -- the optimized code gives us a different
result for:
  a = TRUE
  b = FALSE
  x = 0
  y = 0