Do not gcse unreachable code

During global CSE we now ignore nodes in unreachable blocks,
otherwise cse could pick the wrong representative node
and use unreachable nodes in reachable code.

ir/ir/iropt.c

@@ -6129,6 +6129,16 @@ ir_node *identify_remember(ir_node *n)
 	if (value_table == NULL)
 		return n;
 
+	if (get_opt_global_cse()) {
+		/* do not remember unreachable nodes */
+		if (get_irg_dom_state(irg) == dom_consistent && !is_Block(n)) {
+			ir_node *block = get_nodes_block(n);
+			if (get_Block_dom_depth(block) < 0) {
+				return n;
+			}
+		}
+	}
+
 	ir_normalize_node(n);
 	/* lookup or insert in hash table with given hash key. */
 	nn = (ir_node*)pset_insert(value_table, n, ir_node_hash(n));