provides a mechanism for optimizing compilers to select the different Register configuration.

src/register-configuration.h

Index: src/register-configuration.h
diff --git a/src/register-configuration.h b/src/register-configuration.h
index f12bc7c07c6dfb4beb79477f5a88ce16502b4c71..8ad1d783049079a171b13eeefc675a2a4133df7b 100644
--- a/src/register-configuration.h
+++ b/src/register-configuration.h
@@ -14,11 +14,18 @@ namespace internal {
 // for instruction creation.
 class RegisterConfiguration {
  public:
+  // Define the optimized compiler selector for register configuration
+  // selection.
+  //
+  // TODO(X87): This distinction in RegisterConfigurations is temporary
+  // until x87 TF supports all of the registers that Crankshaft does.
+  enum CompilerSelector { CRANKSHAFT, TURBOFAN };
+
   // Architecture independent maxes.
   static const int kMaxGeneralRegisters = 32;
   static const int kMaxDoubleRegisters = 32;
 
-  static const RegisterConfiguration* ArchDefault();
+  static const RegisterConfiguration* ArchDefault(CompilerSelector compiler);
 
   RegisterConfiguration(int num_general_registers, int num_double_registers,
                         int num_allocatable_general_registers,