[Bug tree-optimization/89427] missing -Warray-bounds on a MEM_REF of array plus offset

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89427

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The equivalent code using memcpy (or even strcpy) is diagnosed:

$ cat u.c && gcc -O2 -S -Wall u.c
char a[8];

void f (int i)
{
  char *p = a + sizeof a;
  if (i < 5)
    i = 5;
  __builtin_memcpy (p + i, "", 1);
}
u.c: In function ‘f’:
u.c:8:3: warning: ‘__builtin_memcpy’ offset [13, 2147483655] is out of the
bounds [0, 8] of object ‘a’ with type ‘char[8]’ [-Warray-bounds]
    8 |   __builtin_memcpy (p + i, "", 1);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
u.c:1:6: note: ‘a’ declared here
    1 | char a[8];
      |      ^


Likewise for memset (by -Wstringop-overflow=):

$ cat u.c && gcc -O2 -S -Wall u.c
char a[8];

void f (int i)
{
  char *p = a + sizeof a;
  if (i < 5)
    i = 5;
  __builtin_memset (p + i, 0, 1);
}
u.c: In function ‘f’:
u.c:8:3: warning: ‘__builtin_memset’ writing 1 byte into a region of size 0
overflows the destination [-Wstringop-overflow=]
    8 |   __builtin_memset (p + i, 0, 1);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~