[Bug target/47855] New: missed cbnz optimization

[carrot at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47855

           Summary: missed cbnz optimization
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: carrot@google.com
            Target: arm-linux-androideabi


Created attachment 23440
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23440
testcase

Compile the attached source code with options -march=armv7-a -mthumb -Os, GCC
4.6 generates 

pnm_gethdr:
    @ args = 0, pretend = 0, frame = 8
    @ frame_needed = 0, uses_anonymous_args = 0
    push    {r0, r1, r2, r4, r5, lr}
    mov    r5, r0
    mov    r4, r1
    bl    foo2
    cmp    r0, #0                // A
    bne    .L13                  // B
    adds    r1, r4, #4
    mov    r0, r5
    bl    foo3
    cmp    r0, #0                // C
    bne    .L13                  // D
    add    r1, r4, #8
    mov    r0, r5
    bl    foo1
    cbnz    r0, .L13              // E
    ldr    r0, [r4, #0]
    bl    pnm_type
    cmp    r0, #2
    beq    .L3
    mov    r0, r5
    add    r1, sp, #4
    bl    pnm_getsintstr
    cbz    r0, .L4
    b    .L13
.L3:
    movs    r3, #1
    str    r3, [sp, #4]
.L4:
    ldr    r3, [sp, #4]
    cmp    r3, #0
    bge    .L5
    negs    r3, r3
    str    r3, [r4, #16]
    movs    r3, #1
    b    .L14
.L5:
    str    r3, [r4, #16]
    movs    r3, #0
.L14:
    strb    r3, [r4, #20]
    ldr    r0, [r4, #0]
    bl    pnm_type
    cmp    r0, #0
    beq    .L8
    blt    .L7
    cmp    r0, #2
    bgt    .L7
    movs    r3, #1
    movs    r0, #0
    str    r3, [r4, #12]
    b    .L2
.L8:
    movs    r3, #3
    str    r3, [r4, #12]
    b    .L2
.L7:
    bl    abort
.L13:
    mov    r0, #-1
.L2:
    pop    {r1, r2, r3, r4, r5, pc}

The branch distance of cbz/cbnz is 126 bytes. The size of the whole function is
124 bytes. So instructions AB and CD can be replaced by

     cbnz    r0,  .L13

same as instruction E.