compile.c: check type before checking insn_id

* compile.c (iseq_peephole_optimize): check element type before
  checking insn_id which is valid only for INSN elements.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

compile.c

@@ -1998,7 +1998,13 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
 	 */
 	INSN *nobj = (INSN *)get_destination_insn(iobj);
 	INSN *pobj = (INSN *)iobj->link.prev;
-	int prev_dup = (pobj && pobj->insn_id == BIN(dup));
+	int prev_dup = 0;
+	if (pobj) {
+	    if (pobj->link.type != ISEQ_ELEMENT_INSN)
+		pobj = 0;
+	    else if (pobj->insn_id == BIN(dup))
+		prev_dup = 1;
+	}
 
 	for (;;) {
 	    if (nobj->insn_id == BIN(jump)) {