[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

test/cctest/test-code-stubs-arm.cc

Index: test/cctest/test-code-stubs-arm.cc
diff --git a/test/cctest/test-code-stubs-arm.cc b/test/cctest/test-code-stubs-arm.cc
index f59d85483d693b1ba7754bca047d74b205abb80f..0e0a132146c18527ff59c4ca04d6b733ec51923d 100644
--- a/test/cctest/test-code-stubs-arm.cc
+++ b/test/cctest/test-code-stubs-arm.cc
@@ -78,8 +78,9 @@ ConvertDToIFunc MakeConvertDToIFuncTrampoline(Isolate* isolate,
   int source_reg_offset = kDoubleSize;
   int reg_num = 0;
   for (; reg_num < Register::kNumRegisters; ++reg_num) {
-    Register reg = Register::from_code(reg_num);
-    if (reg.IsAllocatable()) {
+    if (RegisterConfiguration::Crankshaft()->IsAllocatableGeneralCode(
+            reg_num)) {
+      Register reg = Register::from_code(reg_num);
       if (!reg.is(destination_reg)) {
         __ push(reg);
         source_reg_offset += kPointerSize;
@@ -107,8 +108,9 @@ ConvertDToIFunc MakeConvertDToIFuncTrampoline(Isolate* isolate,
 
   // Make sure no registers have been unexpectedly clobbered
   for (--reg_num; reg_num >= 0; --reg_num) {
-    Register reg = Register::from_code(reg_num);
-    if (reg.IsAllocatable()) {
+    if (RegisterConfiguration::Crankshaft()->IsAllocatableGeneralCode(
+            reg_num)) {
+      Register reg = Register::from_code(reg_num);
       if (!reg.is(destination_reg)) {
         __ ldr(ip, MemOperand(sp, 0));
         __ cmp(reg, ip);