[Bug middle-end/43987] [4.5 regression] type-punning causes broken binaries unless -O0 is used

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2010-05-05 13:13 
-------
I see

extern char bb_common_bufsiz1[COMMON_BUFSIZE];

static void add_input_file(FILE *file)
{
 fprintf(stderr, "Adding input file %x.\n", file);
 (*(struct globals*)&bb_common_bufsiz1).input_file_list =
xrealloc_vector_helper(((*(struct
globals*)&bb_common_bufsiz1).input_file_list), (sizeof(((*(struct
globals*)&bb_common_bufsiz1).input_file_list)[0]) << 8) + (2), ((*(struct
globals*)&bb_common_bufsiz1).input_file_count));
 (*(struct globals*)&bb_common_bufsiz1).input_file_list[(*(struct
globals*)&bb_common_bufsiz1).input_file_count++] = file;
 fprintf(stderr, "Added input file %x.\n", (*(struct
globals*)&bb_common_bufsiz1).input_file_list[(*(struct
globals*)&bb_common_bufsiz1).input_file_count-1]);
}

and the store to (*(struct
globals*)&bb_common_bufsiz1).input_file_list[(*(struct
globals*)&bb_common_bufsiz1).input_file_count++] is indeed DSEd
at -O1 or by DCE if the printfs are removed.

Testcase:

extern char B[256 * sizeof(void *)];
typedef void *FILE;
typedef struct globals {
    int c;
    FILE **l;
} T;
void* xrealloc(void *vector, unsigned sizeof_and_shift, int idx);
void add_input_file(FILE *file)
{
  (*(T*)&B).l = xrealloc(((*(T*)&B).l),
                         (sizeof(((*(T*)&B).l)[0]) << 8) + (2),
                         ((*(T*)&B).c));
  (*(T*)&B).l[(*(T*)&B).c++] = file;
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-05-05 13:13:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43987