[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.