[Bug tree-optimization/53805] New: combine_comparisons changes trapping behavior

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53805

             Bug #: 53805
           Summary: combine_comparisons changes trapping behavior
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: gli...@gcc.gnu.org


Hello,

int f(double a,double b){
  if(a>b) if(a<b) return 1;
  return 0;
}

gets simplified by tree-ssa-ifcombine to just return 0; which is wrong if the
comparison would trap.

This is caused by combine_comparisons:

        bool trap = (compcode & COMPCODE_UNORD) == 0
                    && (compcode != COMPCODE_EQ)
                    && (compcode != COMPCODE_ORD);

which is missing:

                    && (compcode != COMPCODE_FALSE)

(this isn't needed for ltrap and rtrap)