Re: [C++0x] contiguous bitfields race implementation

[Aldy Hernandez <aldyh at redhat dot com>]

> I believe that any after-the-fact attempt to recover bitfield boundaries is
> going to fail unless you preserve more information during bitfield layout.
>
> Consider
>
> struct {
>    char : 8;
>    char : 0;
>    char : 8;
> };
>
> where the : 0 isn't preserved in any way and you can't distinguish
> it from struct { char : 8; char : 8; }.

Huh?  In my tests the :0 is preserved, it just doesn't have a DECL_NAME.

(gdb) p fld
$41 = (tree) 0x7ffff7778130
(gdb) pt
 <field_decl 0x7ffff7778130 D.1593
...

I have tried the following scenario, and we calculate the beginning of 
the bit region correctly (bit 32).

struct bits
{
  char a;
  int b:7;
  int :0;		<-- bitregion start
  int c:9;		<-- bitregion start
  unsigned char d;
} *p;

void foo() { p -> c = 55; }

Am I misunderstanding?  Why do you suggest we need to preserve more 
information during bitfield layout?

FWIW, I should add a zero-length bit test.