[Bug regression/16456] New: PowerPC - redundant subtract involving pointer types

["gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Description:
A non-optimal code sequence is illustrated.  Two subtract operations are
done where only one is necessary.  Duplicate using gcc 3.5 and command
line:

gcc -O3 -m64 -c test.c

Testcase:
char * ptr1;
char * ptr2;
int x;
long int y;

void foo ()
{
    x = ptr1 - ptr2;
    y = ptr1 - ptr2;
}

Assembly:
      ld 9,.LC0@toc(2)
      ld 11,.LC1@toc(2)
      ld 0,0(9)
      ld 10,0(11)
      ld 8,.LC3@toc(2)
      subf 11,10,0
      ld 9,.LC2@toc(2)
      subf 0,10,0  -- no need to do this subtract, just use the previous
result.
      std 11,0(8)
      stw 0,0(9)
      blr



-- 
           Summary: PowerPC - redundant subtract involving pointer types
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P1
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steinmtz at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
                    dot com
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16456