Hi Martin,
On Wed, 23 Oct 2013 19:11:06, Martin Jambor wrote:
> On Wed, Oct 23, 2013 at 06:00:43PM +0200, Richard Biener wrote:
>>
>
> ...
>
>> ? And why should the same issue not exist for
>>
>> struct { V a[1]; }
>>
>
> indeed, it does and it's simple to trigger (on x86_64):
>
> ----------------------------------------
> /* { dg-do run } */
>
> #include <stdlib.h>
>
> typedef long long V
> __attribute__ ((vector_size (2 * sizeof (long long)), may_alias));
>
> #if 1
> typedef struct S {V b[1]; } P __attribute__((aligned (1)));
> struct __attribute__((packed)) T { char c; P s; };
> #else
> typedef struct S {V b[1]; } P;
> struct T { char c; P s; };
> #endif
>
> void __attribute__((noinline, noclone))
> good_value (V b)
> {
> if (b[0] != 3 || b[1] != 4)
> __builtin_abort ();
> }
>
> void __attribute__((noinline, noclone))
> check (P *p)
> {
> good_value (p->b[1]);
> }
>
> int
> main ()
> {
> struct T *t = (struct T *) calloc (128, 1);
> V a = { 3, 4 };
> t->s.b[1] = a;
> check (&t->s);
> free (t);
> return 0;
> }
> ----------------------------------------
>
> While I was willing to discount the zero sized array as an
> insufficiently specified oddity, this seems to be much more serious
> and potentially common. It seems we really need to be able to detect
> these out-of-bounds situations and tell lower levels of expander that
> "whatever mode you think you are expanding, it is actually BLK mode."
>
> It's uglier than I thought.
>
> Martin
>
Deja-vu...
Thanks for this test case. This definitely destroys the idea to fix this in
stor-layout.c
I think that is common practice to write array[1]; at the end of the structure,
and use it as a flexible array. The compute_record_mode has no way to
decide if that is going to be a flexible array or not.
Sorry Eric, but now I have no other choice than to go back to my previous
version
of part 2:
http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00222.html
I'd just add Martin's new test case as 57748-4.c.
Bernd.
