Extracting the size of a variable from its tree representation

I have written a modification of the function "lower_omp_clauses" inside gcc/omp-low.c .  Whenever this
function encounters an OpenMP reduction clause, my code needs to get the type and size of the reduction
variable.   (By size, I mean the integer constant equal to the result of the sizeof operator applied to that
variable.)  I have managed to do this so far for C target code, but I've run into a problem with a Fortran
program that has a reduction on a variable of type "double precision" (i.e., double).  My code reports the
type, correctly, as REAL_TYPE, but it reports the size erroneously as 0 instead of 8.

Here is a reduced version of how I go about trying to gather my information.  What should I be doing instead,
particularly to get the size?

lower_reduction_clauses (tree clauses, gimple_seq *stmt_seqp, omp_context *ctx)
{
	tree c;
	/* ... */
	for (c = clauses; c ; c = OMP_CLAUSE_CHAIN (c))
	 {
      		tree var, ref, new_var;

		enum tree_code code;
		enum tree_code new_var_type;
		size_t new_var_size;

		location_t clause_loc = OMP_CLAUSE_LOCATION (c);

		var = OMP_CLAUSE_DECL (c);
		new_var = lookup_decl (var, ctx);
		if (is_reference (var))
			new_var = build_simple_mem_ref_loc (clause_loc, new_var);
		ref = build_outer_var_ref (var, ctx);
		code = OMP_CLAUSE_REDUCTION_CODE (c);