[Bug middle-end/97391] New: [11 Regression] bogus -Warray-bounds accessing a multidimensional array parameter

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97391

            Bug ID: 97391
           Summary: [11 Regression] bogus -Warray-bounds accessing a
                    multidimensional array parameter
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Both warnings below are incorrect.

$ cat xx.c && gcc -O2 -S -Wall xx.c
void f (char a[3][5])
{
  for (int i = 0; i < 3; i++)
    for (int j = 0; j < 5; j++)
      a[i][j] = 0;
}
xx.c: In function ‘f’:
xx.c:5:8: warning: array subscript ‘char[5][0]’ is partly outside array bounds
of ‘char[3]’ [-Warray-bounds]
    5 |       a[i][j] = 0;
      |       ~^~~
xx.c:1:14: note: while referencing ‘a’
    1 | void f (char a[3][5])
      |         ~~~~~^~~~~~~
xx.c:5:15: warning: ‘__builtin_memset’ forming offset [3, 14] is out of the
bounds [0, 3] [-Warray-bounds]
    5 |       a[i][j] = 0;
      |       ~~~~~~~~^~~