[Bug middle-end/77594] double computation for __builtin_sub_overflow (0, ...)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77594

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-09-15
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
            case MINUS_EXPR:
              if (integer_zerop (arg0) && !unsr_p)
                expand_neg_overflow (loc, lhs, arg1, false);
              /* FALLTHRU */
            case PLUS_EXPR:
              expand_addsub_overflow (loc, code, lhs, arg0, arg1,
                                      unsr_p, unsr_p, unsr_p, false);
              return;

indeed contains premature optimization (handling 0 - x) and missing a return.