[Bug rtl-optimization/17931] New: andl and testb are not combined

[kazu at cs dot umass dot edu]

Consider:

struct flags {
  unsigned f0 : 1;
  unsigned f1 : 1;
};

_Bool
foo (struct flags *p)
{
  if (p->f0)
    return 1;

  return p->f1;
}

With "cc1 -O2 -fomit-frame-pointer", I get

foo:
        movl    4(%esp), %eax
        movb    (%eax), %dl
        movb    %dl, %al
        andl    $1, %eax
        testb   %al, %al
        jne     .L7
        xorl    %eax, %eax
        testb   $2, %dl
        setne   %al
        ret
        .p2align 2,,3
.L7:
        movl    $1, %eax
        ret

Note that andl and testb are not combined to "testb $1, %al".
If they were combined, we would not destroy %eax,
so we would not need to make a copy of %al for a later use.

With -march=pentium4 or -march=athlon-xp, I get a similar result.

-- 
           Summary: andl and testb are not combined
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17931