[RS6000] fix rtl-checking internal compiler error

	* gcc/config/rs6000/rs6000.c (insn_is_swappable_p): Properly
	look inside UNSPEC_VSX_XXSPLTW vec.

From-SVN: r243097

gcc/ChangeLog

+2016-12-01  Alan Modra  <amodra@gmail.com>
+
+	* gcc/config/rs6000/rs6000.c (insn_is_swappable_p): Properly
+	look inside UNSPEC_VSX_XXSPLTW vec.
+
 2016-12-01  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	PR rtl-optimization/78607

gcc/config/rs6000/rs6000.c

@@ -40675,7 +40675,7 @@ insn_is_swappable_p (swap_web_entry *insn_entry, rtx insn,
 	    if (GET_CODE (use_body) != SET
 		|| GET_CODE (SET_SRC (use_body)) != UNSPEC
 		|| XINT (SET_SRC (use_body), 1) != UNSPEC_VSX_XXSPLTW
-		|| XEXP (XEXP (SET_SRC (use_body), 0), 1) != const0_rtx)
+		|| XVECEXP (SET_SRC (use_body), 0, 1) != const0_rtx)
 	      return 0;
 	  }
 	}