fix arch_dep for mul(x,0)

ir/ir/irarch.c

@@ -572,13 +572,13 @@ ir_node *arch_dep_replace_mul_with_shifts(ir_node *irn)
 	ir_tarval *tv;
 	const ir_settings_arch_dep_t *params = be_get_backend_param()->dep_param;
 
-
 	/* If the architecture dependent optimizations were not initialized
 	   or this optimization was not enabled. */
 	if (params == NULL || (opts & arch_dep_mul_to_shift) == 0)
-		return irn;
+		return res;
 
-	if (!is_Mul(irn) || !mode_is_int(mode))
+	assert(is_Mul(irn));
+	if (!mode_is_int(mode))
 		return res;
 
 	/* we should never do the reverse transformations again
@@ -600,6 +600,11 @@ ir_node *arch_dep_replace_mul_with_shifts(ir_node *irn)
 		operand = left;
 	}
 
+	/* multiplications with 0 are a special case which we leave for
+	 * equivalent_node_Mul because the code here can't handle them */
+	if (tv == get_mode_null(mode))
+		return res;
+
 	if (tv != NULL) {
 		res = do_decomposition(irn, operand, tv);