[Bug middle-end/78115] Missed optimization for "int modulo 2^31"

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78115

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-10-27
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC is pessimized by its own IL (with undefined overflow).  Optimized we have:

  <bb 2>:
  if (num_3(D) < 0)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  _1 = num_3(D) + 1;
  num_4 = _1 + 2147483647;

  <bb 4>:
  # num_2 = PHI <num_3(D)(2), num_4(3)>
  return num_2;

not sure what exactly clang matches here.