simplify-rtx: Fix the last fix (PR78638)

I managed to get the last obvious fix wrong: mode is M1, GET_MODE (op)
is M2.


	* simplify-rtx.c (simplify_truncation): M2 is not mode, it is
	GET_MODE (op).  Fix this.

From-SVN: r243210

gcc/ChangeLog

+2016-12-02  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* simplify-rtx.c (simplify_truncation): M2 is not mode, it is
+	GET_MODE (op).  Fix this.
+
 2016-12-02  David Malcolm  <dmalcolm@redhat.com>
 
 	PR bootstrap/78616

gcc/simplify-rtx.c

@@ -752,7 +752,7 @@ simplify_truncation (machine_mode mode, rtx op,
      changing len.  */
   if ((GET_CODE (op) == ZERO_EXTRACT || GET_CODE (op) == SIGN_EXTRACT)
       && REG_P (XEXP (op, 0))
-      && GET_MODE (XEXP (op, 0)) == mode
+      && GET_MODE (XEXP (op, 0)) == GET_MODE (op)
       && CONST_INT_P (XEXP (op, 1))
       && CONST_INT_P (XEXP (op, 2)))
     {