[Bug c/68971] -Woverflow false alarm in code unreachable after __builtin_mul_overflow

[eggert at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68971

--- Comment #10 from Paul Eggert <eggert at gnu dot org> ---
Unfortunately, the patch for Bug#68120 does not seem to have addressed the
problem here. For example, although the following code uses the new feature
enabled by that patch:

  int f (void) {
    return (__builtin_mul_overflow (0x7fffffff, 0x7fffffff, (int *) 0)
            ? 2
            : 0x7fffffff * 0x7fffffff);
  }

I still get the following warning with GCC 6.3.1 20161221 (Red Hat 6.3.1-1)
x86-64:

t.c: In function ‘f’:
t.c:4:19: warning: integer overflow in expression [-Woverflow]
      : 0x7fffffff * 0x7fffffff);
                   ^