[Bug tree-optimization/99632] New: missing warning accessing a trailing zero length array member of base class

[Bug tree-optimization/99632] New: missing warning accessing a trailing zero length array member of base class

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99632

            Bug ID: 99632
           Summary: missing warning accessing a trailing zero length array
                    member of base class
           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: ---

-Warray-bounds triggers for the invalid access in f() and g() but not in h(). 
All three should be diagnosed.  In addition, the warning in g() should be on
the line with the access.

$ cat t.C && gcc -O2 -S -Wall t.C
struct D: B { int j; };

void f (D *p, int i)
{
  p->a[i] = 0;         // -Warray-bounds (good)
}

void g (D *p, int i)
{
  int *q = &p->a[i];   //-Warray-bounds (should be on next line)
  *q = 0; 
}

void h (D *p, int i)
{
  int *q = p->a;
  q[i] = 0;            // missing warning
}


t.C: In function ‘void f(D*, int)’:
t.C:6:9: warning: array subscript i is outside array bounds of ‘int [0]’
[-Warray-bounds]
    6 |   p->a[i] = 0;         // -Warray-bounds (good)
      |   ~~~~~~^
t.C:1:19: note: while referencing ‘B::a’
    1 | struct B { int n, a[0]; };
      |                   ^
t.C: In function ‘void g(D*, int)’:
t.C:11:19: warning: array subscript i is outside array bounds of ‘int [0]’
[-Warray-bounds]
   11 |   int *q = &p->a[i];   //-Warray-bounds (should be on next line)
      |             ~~~~~~^
t.C:1:19: note: while referencing ‘B::a’
    1 | struct B { int n, a[0]; };
      |                   ^

[Bug tree-optimization/99632] missing warning accessing a trailing zero length array member of base class

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99632

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The code is chopped off and does not declare the struct B.

[Bug tree-optimization/99632] missing warning accessing a trailing zero length array member of base class

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99632

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
The definition missing from comment #0 is:

  struct B { int n, a[0]; };