Identifying a block copy

["Pranav Bhandarkar" <pranav dot bhandarkar at gmail dot com>]

Hi,
consider the following code,

struct x { int a; int b; int c; int d; int e[120];};
struct x *a, *b;
void foo ( )
{
    *a = *b;
}

Now for the stmt int the function foo a memcpy will be generated.
However, this can be tail call optimized. My aim is to identify such
opportunities in find_tail_calls in tree-tailcall.c. However, for the
stmt

*a.0_1 ={v} *b.1_2;

var_can_have_subvars return zero for  *a.0_1 . But  a.0_1 is pointer
to a structure and *a.0_1 is a structure and therefore can have
subvars.

The comment for var_can_have_subvars says
/* Return true if V is a tree that we can have subvars for.
   Normally, this is any aggregate type.  Also complex
   types which are not gimple registers can have subvars.  */

IMHO, var_can_have_subvars for the above case should return true, but
it doesnt because it fails the following test in var_can_have_subvars.
  /* Non decls or memory tags can never have subvars.  */
  if (!DECL_P (v) || MTAG_P (v))
    return false;

Am I missing something here ?

TIA,
Pranav