RE: [PATCH, PR 57748] Check for out of bounds access, Part 2

[Bernd Edlinger]

Hi Eric,

>> Would you agree that this "error: flexible array member"
>> should also be emitted for a zero-sized array member,
>> maybe as "error: zero-sized array member not at end of struct"?
>
> I would have answered yes when zero-sized arrays where introduced, but it's
> far less clear a couple of decades later IMO.

But if zero-sized arrays everywhere in a structure is valid C,
then the attached test case is a valid test case.
And it will break your patch for PR58570 at -O1 and above,
because you can no longer assume that different array members
are not an alias.


Regards
Bernd.                                    
int printf (const char *, ...);

struct S
{
char a[0];
short b[1];
};

int e = 1, i;
static struct S d;

int
main ()
{
  if (e)
    {
      d.b[i]=!d.b[i]; //0->1
      d.a[i]=!d.a[i]; //1->0
      d.b[i]=!d.b[i]; //0->1
    }
  printf ("%d\n", d.b[0]);
  return 0;
}