[Bug tree-optimization/105776] New: Failure to recognize __builtin_mul_overflow pattern

["gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105776

            Bug ID: 105776
           Summary: Failure to recognize __builtin_mul_overflow pattern
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f4(unsigned x, unsigned y)
{
    if (x == 0)
        return 1;
    return ((int)(x * y) / (int)x) == y;
}

can be optimized to

int f4(unsigned x, unsigned y)
{
    int z;
    return !__builtin_mul_overflow((int)x, (int)y, &z);
}

This transformation is done by LLVM, but not by GCC.

Note that this derivates from another function written as such:

int
f3 (unsigned x, unsigned y)
{
  unsigned int r = x * y;
  return !x || ((int) r / (int) x) == (int) y;
}

which does optimize correctly on x86 but not on aarch64 (where it generates
tree-optimized GIMPLE corresponding to the code above)