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

[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    _g3@GOTPCREL(%rip), %rax
        incl    (%rax)
L7:
        testl   %edi, %edi <-- #2
        jne     L10
        movq    _g2@GOTPCREL(%rip), %rax
        movl    (%rax), %eax
        ret
        .align 4,0x90
L10:
        movq    _g1@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

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

[steven at gcc dot gnu dot org]

------- Comment #1 from steven at gcc dot gnu dot org  2010-05-13 23:33 -------
Confirmed, this is a case where a def could be sunk closer to its first use.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2010-05-13 23:33:29
               date|                            |


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