[combine] Don't create LSHIFTRT of zero bits in change_zero_ext

	* combine.c (change_zero_ext): Do not create a shift of zero length.

From-SVN: r231613

gcc/ChangeLog

+2015-12-14  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	* combine.c (change_zero_ext): Do not create a shift of zero length.
+
 2015-12-14  Claudiu Zissulescu  <claziss@synopsys.com>
 
 	* config/arc/arc.c (TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P):

gcc/combine.c

@@ -11045,7 +11045,8 @@ change_zero_ext (rtx *src)
 	  if (BITS_BIG_ENDIAN)
 	    start = GET_MODE_PRECISION (mode) - size - start;
 
-	  x = gen_rtx_LSHIFTRT (mode, XEXP (x, 0), GEN_INT (start));
+	  x = simplify_gen_binary (LSHIFTRT, mode,
+				   XEXP (x, 0), GEN_INT (start));
 	}
       else if (GET_CODE (x) == ZERO_EXTEND
 	       && GET_CODE (XEXP (x, 0)) == SUBREG