[PATCH][ARM] Get mode for rtx costs calculations for SET RTX from destination reg

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

Hi all,

SET RTXs don't have a mode, so the code to calculate a reg-to-reg set in the arm 
rtx costs function needs to get the mode from one of the registers involved. We 
already did that when the source is a CONST_INT.

This patch fixes that oversight and also prevents us from falling through or 
recursing, since the cost calculated for (set (reg) (reg)) should be final at 
that point.

Tested arm-none-eabi on qemu.

Ok for trunk?

Thanks,
Kyrill

2014-01-09  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * config/arm/arm.c (arm_new_rtx_costs): Use destination mode
    when handling a SET rtx.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index c8bf7c1..4c991c2 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -9092,6 +9092,9 @@ arm_new_rtx_costs (rtx x, enum rtx_code code, enum rtx_code outer_code,
     {
     case SET:
       *cost = 0;
+      /* SET RTXs don't have a mode so we get it from the destination.  */
+      mode = GET_MODE (SET_DEST (x));
+
       if (REG_P (SET_SRC (x))
 	  && REG_P (SET_DEST (x)))
 	{
@@ -9106,6 +9109,8 @@ arm_new_rtx_costs (rtx x, enum rtx_code code, enum rtx_code outer_code,
 	     in 16 bits in Thumb mode.  */
 	  if (!speed_p && TARGET_THUMB && outer_code == COND_EXEC)
 	    *cost >>= 1;
+
+	  return true;
 	}
 
       if (CONST_INT_P (SET_SRC (x)))
@@ -9113,7 +9118,6 @@ arm_new_rtx_costs (rtx x, enum rtx_code code, enum rtx_code outer_code,
 	  /* Handle CONST_INT here, since the value doesn't have a mode
 	     and we would otherwise be unable to work out the true cost.  */
 	  *cost = rtx_cost (SET_DEST (x), SET, 0, speed_p);
-	  mode = GET_MODE (SET_DEST (x));
 	  outer_code = SET;
 	  /* Slightly lower the cost of setting a core reg to a constant.
 	     This helps break up chains and allows for better scheduling.  */