[Bug target/43233] New: x86 flags not combined across blocks

[astrange at ithinksw dot com]

Source:
int g1,g2,g3;

int f1(int a, int b)
{
    a &= 1;

    if (a) return g1;
    return g2;
}

int f2(int a, int b)
{
    a &= 1;

    if (b)
        g3++;

    if (a) return g1;
    return g2;
}

Compiled with:
> gcc -O3 -fomit-frame-pointer -S and_flags.c

f1 is ok but f2 generates this:
_f2:
        andl    $1, %edi <-- #1
        testl   %esi, %esi
        je      L7
        movq    _...@gotpcrel(%rip), %rax
        incl    (%rax)
L7:
        testl   %edi, %edi <-- #2
        jne     L10
        movq    _...@gotpcrel(%rip), %rax
        movl    (%rax), %eax
        ret
        .align 4,0x90
L10:
        movq    _...@gotpcrel(%rip), %rax
        movl    (%rax), %eax
        ret

The andl and testl should be folded into one andl.

Code is reduced from ffmpeg h264 decoder. It's easy to work around by
reordering source lines, so not too important.


-- 
           Summary: x86 flags not combined across blocks
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: astrange at ithinksw dot com
  GCC host triplet: x86_64-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43233