[Bug target/45701] New: [regression 4.5] Fail to prefer using r3 for padding a push/pop multiple to 8-byte alignment

["qiyao at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

This was implemented in gcc-4.5, still works in gcc-4.5 branch.
2009-06-02 Richard Earnshaw <rearnsha@arm.com>

        * arm.c (arm_get_frame_offsets): Prefer using r3 for padding a
        push/pop multiple to 8-byte alignment.
However, it doesn't work any longer on gcc-4.6 trunk.  Reproduced on the
following steps,

$ arm-none-linux-gnueabi-gcc -Os -mthumb -march=armv7-a bashline.c -S

On gcc-4.5 branch, r3 is used to keep stack alignment, which is expected.
history_expand_line_internal:
        @ args = 0, pretend = 0, frame = 0 
        @ frame_needed = 0, uses_anonymous_args = 0 
        push    {r3, r4, r5, r6, r7, lr} 

However, on gcc-4.6 trunk, we can see that, r8 is used to keep stack alignment,
which is *not* expected.
history_expand_line_internal:
        @ args = 0, pretend = 0, frame = 0 
        @ frame_needed = 0, uses_anonymous_args = 0 
        push    {r4, r5, r6, r7, r8, lr}


-- 
           Summary: [regression 4.5] Fail to prefer using r3 for padding a
                    push/pop multiple to 8-byte alignment
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: qiyao at gcc dot gnu dot org
  GCC host triplet: i486-build_pc-linux-gnu
GCC target triplet: arm-unknown-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45701