[Bug tree-optimization/23181] New: Dominator opts slows down bresenham line drawing by roughly 20%

[hubicka at gcc dot gnu dot org]

Dominator opts slows down the bresenham line drawing loop by roughly 20%.
-O2 -fno-dominator-opts results in pretty straighline code:
.L14:
        addl    $18, %edx
.L5:
        testl   %edx, %edx
        movb    $5, (%eax)
        js      .L6
        addl    $21, %eax
        subl    $40, %edx
.L6:
        incl    %eax
        cmpl    %eax, %ecx
        jne     .L14

While dominator combines the additions into quite ugly result:
.L5:
        movl    %ecx, %edx
        addl    $18, %edx
        movb    $5, 1(%ebx)
        js      .L6
        leal    22(%ebx), %eax
        leal    -22(%ecx), %edx
.L6:
        movl    %eax, %ebx
        movl    %edx, %ecx
        leal    1(%ebx), %eax
        cmpl    %eax, %esi
        jne     .L5
.L15:

-- 
           Summary: Dominator opts slows down bresenham line drawing by
                    roughly 20%
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hubicka at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23181