[Bug regression/40886] New: No loop counter reversal for simple loops anymore

[andi-gcc at firstfloor dot org]

Given this simple program:

main()
{
        int i;
        for (i = 0; i < 10; i++) 
                f2();
}

compiled with -O2
gcc33-hammer detects that the loop index is not used in the loop body
and rewrites it to a downwards counting loop, elimitinating one instruction
(inc/cmp -> dec)

  movl    $9, %ebx
        .p2align 4,,7
.L6:
        xorl    %eax, %eax
        call    f2
        decl    %ebx
        jns     .L6
        popq    %rbx

but gcc 4.0 - 4.3 don't anymore (tried 4.1, 4.3 and 4.4):

       xorl    %ebx, %ebx
        .p2align 4,,7
.L2:
        xorl    %eax, %eax
        incl    %ebx
        call    f2
        cmpl    $10, %ebx
        jne     .L2


-- 
           Summary: No loop counter reversal for simple loops anymore
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
  GCC host triplet: x86_64-linux
GCC target triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40886