[Bug c/16856] New: Missed optimisation opportunity with -O2

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

The following code is not optimised optimally with -O2.  The two branches of the
conditional have the same effect, so the conditional can be removed entirely.  

The conditional is removed with -Os, so gcc is capable of carrying out the
optimisation; it just isn't happening at -O2.

$ cat temp.c
static int bar;
static long baz;
 
int foo (_Bool x)
{
    int y;
    if (x) {
        ++baz;
        y = bar;
    }
    else {
        y = bar;
        ++baz;
    }
    return y;
}


$ gcc35 -S -O2 -fomit-frame-pointer -o temp-O2.s temp.c 
$ cat temp-O2.s
...
foo:
        cmpb    $0, 4(%esp)
        je      .L2
        incl    baz
        movl    bar, %eax
        ret
        .p2align 2,,3
.L2:
        movl    bar, %eax
        incl    baz
        ret
...
        .ident  "GCC: (GNU) 3.5.0 20040715 (Red Hat 3.5.0-0.7)"

-- 
           Summary: Missed optimisation opportunity with -O2
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ralph at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16856