refinement performance improvement

vm_method.c.diff

diff --git a/vm_method.c b/vm_method.c
index e44782c..bf02c2c 100644
--- a/vm_method.c
+++ b/vm_method.c
@@ -407,8 +407,10 @@ search_method(VALUE klass, ID id, VALUE omod, VALUE *defined_class_ptr)
 	    iclass = rb_hash_lookup(omod, klass);
 	    if (NIL_P(iclass) && BUILTIN_TYPE(klass) == T_ICLASS) {
 		iclass = rb_hash_lookup(omod, RBASIC(klass)->klass);
-		if (!NIL_P(iclass))
+		if (!NIL_P(iclass)) {
 		    iclass = copy_refinement_iclass(iclass, klass);
+		    rb_hash_aset(omod, klass, iclass);
+		}
 	    }
 	    if (!NIL_P(iclass)) {
 		skipped_class = klass;