[Bug tree-optimization/52070] New: missing integer comparison optimization

[Bug tree-optimization/52070] New: missing integer comparison optimization

[drepper.fsp at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52070

             Bug #: 52070
           Summary: missing integer comparison optimization
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: drepper.fsp@gmail.com


Compile this code with gcc 4.6.2:

#include <stddef.h>
size_t b;
int f(size_t a)
{
  return b == 0 || a < b;
}

For x86-64 I see this result:

f:    movq    b(%rip), %rdx
    movl    $1, %eax
    testq    %rdx, %rdx
    je    .L2
    xorl    %eax, %eax
    cmpq    %rdi, %rdx
    seta    %al
.L2:    rep ret

This can be more done without a conditional jump:

f:    movq    b(%rip), %rdx
    xorl    %eax, %eax
    subq    $1, %rdx
    cmpq    %rdi, %rdx
    setae    %al
    rep ret

Unless the b==0 test is marked as likely I'd say this code is performing better
on all architectures.

[Bug tree-optimization/52070] missing integer comparison optimization

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52070

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-02-01
     Ever Confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-01 02:31:51 UTC ---
Confirmed, I have a few patches which might improve this but maybe not for
x86_64; it does help MIPS right now.

[Bug tree-optimization/52070] missing integer comparison optimization

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52070

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug middle-end/52070] missing integer comparison optimization

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52070

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2012-02-01 00:00:00         |2021-7-26
          Component|tree-optimization           |middle-end

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  _6 = b.1_1 > a_4(D);
  _7 = b.1_1 == 0;
  _8 = _6 | _7;

So this is an expansion issue I think.

[Bug middle-end/52070] missing integer comparison optimization

[roger at nextmovesoftware dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52070

Roger Sayle <roger at nextmovesoftware dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |roger at nextmovesoftware dot com
         Resolution|---                         |FIXED
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=96674
   Target Milestone|---                         |13.0
             Status|NEW                         |RESOLVED

--- Comment #3 from Roger Sayle <roger at nextmovesoftware dot com> ---
This has been fixed (optimally) since GCC 13, by Eugene Rozenfeld's fix for PR
tree-optimization/96674.  The conditional jump was eliminated back in GCC 4.9,
but the combination of the two tests into a subtraction and a single comparison
was implemented (at the tree level) by Eugene.