[Bug c/50081] New: Wrong code (wrong order) generated with -O2 or -Os while function return a struct

["lingyouzeng at arimacomm-hz dot cn" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50081

             Bug #: 50081
           Summary: Wrong code (wrong order) generated with -O2 or -Os
                    while function return a struct
    Classification: Unclassified
           Product: gcc
           Version: 4.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: lingyouzeng@arimacomm-hz.cn


The code like:
typedef struct {
  struct umdb_list_head_st *list_head;
  struct umdb_list_node_st *current;
} umdb_util_it_t;
typedef umdb_util_it_t umdb_dbms_hl_oper_list_iterator_t;

umdb_dbms_hl_oper_list_iterator_t 
umdb_dbms_oper_list_find_element (umdb_dbms_hl_oper_list_handle_t *list, 
                                  MSF_UINT8 src_mod_id,
                                  MSF_UINT16 transaction_id)
{
  umdb_dbms_hl_oper_list_iterator_t it;
  umdb_dbms_oper_list_elem_t *elem;

  it = umdb_dbms_oper_list_get_iterator (list);

  while (!umdb_dbms_oper_list_equals_end (&it)) {
    elem = (umdb_dbms_oper_list_elem_t*)it.current;

    if (elem->ml_transaction_id == transaction_id &&
        elem->src_mod_id == src_mod_id) {
      break;
    }

    umdb_dbms_oper_list_iterator_next (&it);
  }

  return it;
}

The asm code like:
00000000 <umdb_dbms_oper_list_find_element>:
   0:    b5f0          push    {r4, r5, r6, r7, lr}
   2:    b087          sub    sp, #28
   4:    ac02          add    r4, sp, #8
   6:    1c05          adds    r5, r0, #0
   8:    ae04          add    r6, sp, #16
   a:    1c20          adds    r0, r4, #0
   c:    1c17          adds    r7, r2, #0
   e:    9301          str    r3, [sp, #4]
  10:    f7ff fffe     bl    0 <umdb_dbms_oper_list_find_element>
  14:    cc03          ldmia    r4!, {r0, r1}
  16:    c603          stmia    r6!, {r0, r1}
  18:    e00a          b.n    30 <umdb_dbms_oper_list_find_element+0x30>
  1a:    6863          ldr    r3, [r4, #4]
  1c:    9801          ldr    r0, [sp, #4]
  1e:    8a1a          ldrh    r2, [r3, #16]
  20:    4282          cmp    r2, r0
  22:    d102          bne.n    2a <umdb_dbms_oper_list_find_element+0x2a>
  24:    7a1b          ldrb    r3, [r3, #8]
  26:    42bb          cmp    r3, r7
  28:    d008          beq.n    3c <umdb_dbms_oper_list_find_element+0x3c>
  2a:    a804          add    r0, sp, #16
  2c:    f7ff fffe     bl    0 <umdb_dbms_oper_list_find_element>
  30:    ac04          add    r4, sp, #16
  32:    1c20          adds    r0, r4, #0
  34:    f7ff fffe     bl    0 <umdb_dbms_oper_list_find_element>
  38:    2800          cmp    r0, #0
  3a:    d0ee          beq.n    1a <umdb_dbms_oper_list_find_element+0x1a>
  3c:    1c2a          adds    r2, r5, #0
  3e:    ab04          add    r3, sp, #16
  40:    b007          add    sp, #28
  42:    cb03          ldmia    r3!, {r0, r1}
  44:    c203          stmia    r2!, {r0, r1}
  46:    1c28          adds    r0, r5, #0
  48:    bdf0          pop    {r4, r5, r6, r7, pc}
  4a:    46c0          nop            ; (mov r8, r8)

It show the return struct is not safe here, it still use the stack after
sp+0x28.
  40:    b007          add    sp, #28
  42:    cb03          ldmia    r3!, {r0, r1}
  44:    c203          stmia    r2!, {r0, r1}