Support ofsetted parameters in local modref

[Jan Hubicka]

> > So I implemented my own pattern matching and I think we should switch ipa-prop
> > on it incrementally. It is based on similar logic in
> > ao_ref_init_from_ptr_and_size.
> 
> So instead of re-inventing the wheel what about splitting out a
> common helper instead?

It was my original idea. However it is not completely trivial:
ao_ref_init_from_ptr_and_size does bit something else since it is trying
to keep the original ref inside ADDR_EXPR (if one is found) to feed it
into oracle rather then stripping them all.  If refs are present it does
not need to build MEM_REF.

static void
ao_ref_init_from_ptr_and_range (ao_ref *ref, tree ptr,
				bool range_known,
				poly_int64 offset,
				poly_int64 size,
				poly_int64 max_size)
{
  poly_int64 t, extra_offset = 0;

  ref->ref = NULL_TREE;
  if (TREE_CODE (ptr) == SSA_NAME)
    {
      gimple *stmt = SSA_NAME_DEF_STMT (ptr);
      if (gimple_assign_single_p (stmt)
	  && gimple_assign_rhs_code (stmt) == ADDR_EXPR)
	ptr = gimple_assign_rhs1 (stmt);
      else if (is_gimple_assign (stmt)
	       && gimple_assign_rhs_code (stmt) == POINTER_PLUS_EXPR
	       && ptrdiff_tree_p (gimple_assign_rhs2 (stmt), &extra_offset))
	{
	  ptr = gimple_assign_rhs1 (stmt);
	  extra_offset *= BITS_PER_UNIT;
	}
    }

  if (TREE_CODE (ptr) == ADDR_EXPR)
    {
      ref->base = get_addr_base_and_unit_offset (TREE_OPERAND (ptr, 0), &t);
      if (ref->base)
	ref->offset = BITS_PER_UNIT * t;
      else
	{
	  range_known = false;
	  ref->offset = 0;
	  ref->base = get_base_address (TREE_OPERAND (ptr, 0));
	}
    }
  else
    {
      gcc_assert (POINTER_TYPE_P (TREE_TYPE (ptr)));
      ref->base = build2 (MEM_REF, char_type_node,
			  ptr, null_pointer_node);
      ref->offset = 0;
    }

I could add a flag if I am looking for ADDR_EXPR or just the base
pointer but it seemed more for incremental change.  The new helper
should be immediately useful for ipa-modref, ipa-prop and
ipa-polymorphic-call though.

Honza