[Bug c++/26534] [4.1/4.2 Regression] bitfield wrong optimize

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

------- Comment #2 from rguenth at gcc dot gnu dot org  2006-03-03 12:07 -------
The C frontend warns:

t.c: In function ?main?:
t.c:9: warning: large integer implicitly truncated to unsigned type


and has in .gimple:

main ()
{
  <unnamed type> D.1770;
  int D.1771;
  int D.1772;
  struct X x;

  x.a = 15;
  D.1770 = x.a;
  D.1771 = (int) D.1770;
  printf (&"%u\n"[0], D.1771);
  D.1772 = 0;
  return D.1772;
}

The C++ fronted does not warn and creates:

  unsigned int D.2483;
  int D.2484;

  {
    struct X x;

    x.a = 63;
    D.2483 = x.a;

where it should have truncated the constant, as the type as far as the
middle-end is concerned of x.a is

(gdb) call debug_tree(0x402474ac)
 <field_decl 0x402474ac a
    type <integer_type 0x4019e2e0 unsigned int public unsigned SI
        size <integer_cst 0x4018d3d8 constant invariant 32>
        unit size <integer_cst 0x4018d168 constant invariant 4>
        align 32 symtab 0 alias set -1 precision 32 min <integer_cst 0x4018d450
0> max <integer_cst 0x4018d438 4294967295>>
    used unsigned external nonlocal bit-field nonaddressable decl_3 decl_4 SI
file t.C line 3
    size <integer_cst 0x40211af8 type <integer_type 0x4019e05c bit_size_type>
constant invariant 4>
    unit size <integer_cst 0x4018d1f8 type <integer_type 0x4019e000 unsigned
int> constant invariant 1>
    align 1 offset_align 128
    offset <integer_cst 0x4018d180 type <integer_type 0x4019e000 unsigned int>
constant invariant 0>
    bit offset <integer_cst 0x4018d948 type <integer_type 0x4019e05c
bit_size_type> constant invariant 0> context <record_type 0x40247450 X> chain
<type_decl 0x402149c0 X>>

i.e., only the FIELD_DECL knows about the correct precision.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|tree-optimization           |c++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26534