[Bug rtl-optimization/30967] New: Extra sign/zero extend with word comparison result

[pinskia at gcc dot gnu dot org]

Testcase:
int f1(int a, int b)
{
  return a == b;
}

------
We produce right now:
_f1:
        xor r4,r3,r4
        cntlzw r4,r4  <--- sign never 1
        srwi r4,r4,5  <--- upper bits defined as 0
        extsw r3,r4
        blr

The sign extend is incorrect as r4's sign will never be 1 and all the upper
bits will always be zero because of srwi.
we have the same issue if the return value is unsigned int also in that there
is an extra zero extend.

This is even with -fsee.


-- 
           Summary: Extra sign/zero extend with word comparison result
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
GCC target triplet: powerpc64-apple-darwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30967