revert: combine.c (can_change_dest_mode): Reject changes in REGMODE_NATURAL_SIZE.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	Revert accidental duplicate:

	* combine.c (can_change_dest_mode): Reject changes in
	REGMODE_NATURAL_SIZE.

From-SVN: r254316

gcc/ChangeLog

+2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	Revert accidental duplicate:
+
+	* combine.c (can_change_dest_mode): Reject changes in
+	REGMODE_NATURAL_SIZE.
+
 2017-11-01  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	PR rtl-optimization/64682

gcc/combine.c

@@ -2478,12 +2478,6 @@ can_change_dest_mode (rtx x, int added_sets, machine_mode mode)
       != REGMODE_NATURAL_SIZE (GET_MODE (x)))
     return false;
 
-  /* Don't change between modes with different underlying register sizes,
-     since this could lead to invalid subregs.  */
-  if (REGMODE_NATURAL_SIZE (mode)
-      != REGMODE_NATURAL_SIZE (GET_MODE (x)))
-    return false;
-
   regno = REGNO (x);
   /* Allow hard registers if the new mode is legal, and occupies no more
      registers than the old mode.  */