[Bug tree-optimization/99474] New: missing warning on an out of bounds VLA access by a pointer

["msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99474

            Bug ID: 99474
           Summary: missing warning on an out of bounds VLA access by a
                    pointer
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The out of bounds access in both functions below should be diagnosed by
-Warray-bounds but only the first one is.

$ cat v.c && gcc -O2 -S -Wall v.c
void f (void*);

void g (void)
{
  int a[5];
  int *p = &a[0];
  p[5] = 0;        // -Warray-bounds (good)
  f (a);
}

void h (int n)
{
  if (n > 5)
    n = 5;
  int a[n];
  int *p = &a[0];
  p[5] = 0;        // missing warning
  f (a);
}

v.c: In function ‘g’:
v.c:7:4: warning: array subscript 5 is outside array bounds of ‘int[5]’
[-Warray-bounds]
    7 |   p[5] = 0;        // -Warray-bounds (good)
      |   ~^~~
v.c:5:7: note: while referencing ‘a’
    5 |   int a[5];
      |       ^