[ARM] Enable arm_legitimize_address for Thumb-2

Currently arm_legitimize_address doesn't handle Thumb-2 at all, resulting in
inefficient code.  Since Thumb-2 supports similar address offsets use the Arm
legitimization code for Thumb-2 to get significant codesize and performance
gains.  SPECINT2006 shows 0.4% gain on Cortex-A57, while SPECFP improves 0.2%.

    gcc/
	* config/arm/arm.c (arm_legitimize_address): Remove Thumb-2 bailout.

From-SVN: r276961

gcc/ChangeLog

 2019-10-14  Wilco Dijkstra  <wdijkstr@arm.com>
 
+	* config/arm/arm.c (arm_legitimize_address): Remove Thumb-2 bailout.
+
+2019-10-14  Wilco Dijkstra  <wdijkstr@arm.com>
+
 	* config/arm/arm.c (arm_option_override): Don't override sched
 	pressure algorithm.
 

gcc/config/arm/arm.c

@@ -8934,13 +8934,8 @@ arm_legitimize_address (rtx x, rtx orig_x, machine_mode mode)
 	return x;
     }
 
-  if (!TARGET_ARM)
-    {
-      /* TODO: legitimize_address for Thumb2.  */
-      if (TARGET_THUMB2)
-        return x;
+  if (TARGET_THUMB1)
     return thumb_legitimize_address (x, orig_x, mode);
-    }
 
   if (GET_CODE (x) == PLUS)
     {