[Bug c++/84196] New: invalid instantiation of a function template on a vector type silently accepted

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84196

            Bug ID: 84196
           Summary: invalid instantiation of a function template on a
                    vector type silently accepted
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC rejects invalid calls to ordinary functions that take a vector argument but
it silently accepts and emits bogus code for the invalid code below.  Rather
than doing that, it should reject it similarly to how Clang does.

$ cat t.C && gcc -O2 -Wall -Wextra -fdump-tree-optimized=/dev/stdout t.C
template <class T>
int f (T v __attribute__ ((vector_size (16))))
{
  return v[0] + v[1] + v[2] + v[3];
}

int main ()
{
  return f (12345678);
}

;; Function f<int> (_Z1fIiEiT_, funcdef_no=2, decl_uid=2359, cgraph_uid=1,
symbol_order=1)

f<int> (vector(4) int v)
{
  int _1;
  int _2;
  int _3;
  int _4;
  int _5;
  int _6;
  int _8;

  <bb 2> [local count: 1073741825]:
  _1 = BIT_FIELD_REF <v_9(D), 32, 0>;
  _2 = BIT_FIELD_REF <v_9(D), 32, 32>;
  _3 = _1 + _2;
  _4 = BIT_FIELD_REF <v_9(D), 32, 64>;
  _5 = _3 + _4;
  _6 = BIT_FIELD_REF <v_9(D), 32, 96>;
  _8 = _5 + _6;
  return _8;

}



;; Function main (main, funcdef_no=1, decl_uid=2357, cgraph_uid=0,
symbol_order=0) (executed once)

main ()
{
  int _2;

  <bb 2> [local count: 1073741825]:
  _2 = f<int> (12345678); [tail call]
  return _2;

}


Clang gives the following error:

t.C:2:28: error: invalid vector element type 'T'
int f (T v __attribute__ ((vector_size (16))))
                           ^
t.C:4:10: error: subscripted value is not an array, pointer, or vector
  return v[0] + v[1] + v[2] + v[3];
         ^ ~
t.C:9:10: note: in instantiation of function template specialization 'f<int>'
requested here
  return f (12345678);
         ^
2 errors generared