* rtlanal.c (rtx_cost): Handle TRUNCATE between tieable modes.

From-SVN: r247881

gcc/ChangeLog

+2017-05-11  Bin Cheng  <bin.cheng@arm.com>
+
+	* rtlanal.c (rtx_cost): Handle TRUNCATE between tieable modes.
+
 2017-05-11  Richard Biener  <rguenther@suse.de>
 
 	* passes.c (execute_function_todo): Verify loops if they are

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;