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

src/register-configuration.cc

Index: src/register-configuration.cc
diff --git a/src/register-configuration.cc b/src/register-configuration.cc
index 084e735af1e9c2346af612984f4b9cdb2ac769e5..99afcc1e5e12685e70d4ad350b820532fee68410 100644
--- a/src/register-configuration.cc
+++ b/src/register-configuration.cc
@@ -36,7 +36,7 @@ STATIC_ASSERT(RegisterConfiguration::kMaxDoubleRegisters >=
 
 class ArchDefaultRegisterConfiguration : public RegisterConfiguration {
  public:
-  ArchDefaultRegisterConfiguration()
+  explicit ArchDefaultRegisterConfiguration(JITCompiler compiler)
       : RegisterConfiguration(
             Register::kNumRegisters, DoubleRegister::kMaxNumRegisters,
 #if V8_TARGET_ARCH_IA32
@@ -44,7 +44,9 @@ class ArchDefaultRegisterConfiguration : public RegisterConfiguration {
             kMaxAllocatableDoubleRegisterCount,
             kMaxAllocatableDoubleRegisterCount,
 #elif V8_TARGET_ARCH_X87
-            kMaxAllocatableGeneralRegisterCount, 1, 1,
+            kMaxAllocatableGeneralRegisterCount,
+            compiler == TURBOFAN ? 1 : kMaxAllocatableDoubleRegisterCount,
+            compiler == TURBOFAN ? 1 : kMaxAllocatableDoubleRegisterCount,
 #elif V8_TARGET_ARCH_X64
             kMaxAllocatableGeneralRegisterCount,
             kMaxAllocatableDoubleRegisterCount,
@@ -104,16 +106,33 @@ class ArchDefaultRegisterConfiguration : public RegisterConfiguration {
 };
 
 
-static base::LazyInstance<ArchDefaultRegisterConfiguration>::type
-    kDefaultRegisterConfiguration = LAZY_INSTANCE_INITIALIZER;
+template <JITCompiler compiler>
+struct RegisterConfigurationInitializer {
+  static void Construct(ArchDefaultRegisterConfiguration* config) {
+    new (config) ArchDefaultRegisterConfiguration(compiler);
+  }
+};
+
+static base::LazyInstance<ArchDefaultRegisterConfiguration,
+                          RegisterConfigurationInitializer<CRANKSHAFT>>::type
+    kDefaultRegisterConfigurationForCrankshaft = LAZY_INSTANCE_INITIALIZER;
+
+
+static base::LazyInstance<ArchDefaultRegisterConfiguration,
+                          RegisterConfigurationInitializer<TURBOFAN>>::type
+    kDefaultRegisterConfigurationForTurboFan = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 
-const RegisterConfiguration* RegisterConfiguration::ArchDefault() {
-  return &kDefaultRegisterConfiguration.Get();
+const RegisterConfiguration* RegisterConfiguration::ArchDefault(
+    JITCompiler compiler) {
+  return compiler == TURBOFAN
+             ? &kDefaultRegisterConfigurationForTurboFan.Get()
+             : &kDefaultRegisterConfigurationForCrankshaft.Get();
 }
 
+
 RegisterConfiguration::RegisterConfiguration(
     int num_general_registers, int num_double_registers,
     int num_allocatable_general_registers, int num_allocatable_double_registers,