diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index 321363f..d9f57c3 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -4164,6 +4164,13 @@ rtx_cost (rtx x, machine_mode mode, enum rtx_code outer_code,
 	return COSTS_N_INSNS (2 + factor);
       break;
 
+    case TRUNCATE:
+      if (MODES_TIEABLE_P (mode, GET_MODE (XEXP (x, 0))))
+	{
+	  total = 0;
+	  break;
+	}
+      /* FALLTHRU */
     default:
       if (targetm.rtx_costs (x, mode, outer_code, opno, &total, speed))
 	return total;