[runtime] Optimize and unify rest parameters.

src/runtime/runtime-scopes.cc

Index: src/runtime/runtime-scopes.cc
diff --git a/src/runtime/runtime-scopes.cc b/src/runtime/runtime-scopes.cc
index 997e405bffa056efbe27d938928ca46892201417..0867f68b60eba2f098564ffb658787c19a29ced1 100644
--- a/src/runtime/runtime-scopes.cc
+++ b/src/runtime/runtime-scopes.cc
@@ -588,26 +588,6 @@ Handle<JSObject> NewStrictArguments(Isolate* isolate, Handle<JSFunction> callee,
 }
 
 
-template <typename T>
-Handle<JSObject> NewRestArguments(Isolate* isolate, Handle<JSFunction> callee,
-                                  T parameters, int argument_count,
-                                  int start_index) {
-  int num_elements = std::max(0, argument_count - start_index);
-  Handle<JSObject> result = isolate->factory()->NewJSArray(
-      FAST_ELEMENTS, num_elements, num_elements, Strength::WEAK,
-      DONT_INITIALIZE_ARRAY_ELEMENTS);
-  {
-    DisallowHeapAllocation no_gc;
-    FixedArray* elements = FixedArray::cast(result->elements());
-    WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
-    for (int i = 0; i < num_elements; i++) {
-      elements->set(i, parameters[i + start_index], mode);
-    }
-  }
-  return result;
-}
-
-
 class HandleArguments BASE_EMBEDDED {
  public:
   explicit HandleArguments(Handle<Object>* array) : array_(array) {}
@@ -658,19 +638,29 @@ RUNTIME_FUNCTION(Runtime_NewStrictArguments_Generic) {
 }
 
 
-RUNTIME_FUNCTION(Runtime_NewRestArguments_Generic) {
+RUNTIME_FUNCTION(Runtime_NewRestParameter) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 2);
+  DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, callee, 0)
-  CONVERT_SMI_ARG_CHECKED(start_index, 1);
+  int start_index = callee->shared()->internal_formal_parameter_count();
   // This generic runtime function can also be used when the caller has been
   // inlined, we use the slow but accurate {GetCallerArguments}.
   int argument_count = 0;
   base::SmartArrayPointer<Handle<Object>> arguments =
       GetCallerArguments(isolate, &argument_count);
-  HandleArguments argument_getter(arguments.get());
-  return *NewRestArguments(isolate, callee, argument_getter, argument_count,
-                           start_index);
+  int num_elements = std::max(0, argument_count - start_index);
+  Handle<JSObject> result = isolate->factory()->NewJSArray(
+      FAST_ELEMENTS, num_elements, num_elements, Strength::WEAK,
+      DONT_INITIALIZE_ARRAY_ELEMENTS);
+  {
+    DisallowHeapAllocation no_gc;
+    FixedArray* elements = FixedArray::cast(result->elements());
+    WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
+    for (int i = 0; i < num_elements; i++) {
+      elements->set(i, *arguments[i + start_index], mode);
+    }
+  }
+  return *result;
 }
 
 
@@ -708,25 +698,6 @@ RUNTIME_FUNCTION(Runtime_NewStrictArguments) {
 }
 
 
-RUNTIME_FUNCTION(Runtime_NewRestParam) {
-  HandleScope scope(isolate);
-  DCHECK(args.length() == 3);
-  CONVERT_SMI_ARG_CHECKED(num_params, 0);
-  Object** parameters = reinterpret_cast<Object**>(args[1]);
-  CONVERT_SMI_ARG_CHECKED(rest_index, 2);
-#ifdef DEBUG
-  // This runtime function does not materialize the correct arguments when the
-  // caller has been inlined, better make sure we are not hitting that case.
-  JavaScriptFrameIterator it(isolate);
-  DCHECK(!it.frame()->HasInlinedFrames());
-#endif  // DEBUG
-  Handle<JSFunction> callee;
-  ParameterArguments argument_getter(parameters);
-  return *NewRestArguments(isolate, callee, argument_getter, num_params,
-                           rest_index);
-}
-
-
 RUNTIME_FUNCTION(Runtime_NewClosure) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());