Partial revert of rest parameter desugaring.

src/runtime/runtime-scopes.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/ast/scopeinfo.h"
 #include "src/ast/scopes.h"
@@ skipping 587 matching lines @@
   // 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
   ParameterArguments argument_getter(parameters);
   return *NewStrictArguments(isolate, callee, argument_getter, argument_count);
 }
 
 
+static Handle<JSArray> NewRestParam(Isolate* isolate, Object** parameters,
+                                    int num_params, int rest_index,
+                                    LanguageMode language_mode) {
+  parameters -= rest_index;
+  int num_elements = std::max(0, num_params - rest_index);
+  Handle<FixedArray> elements =
+      isolate->factory()->NewUninitializedFixedArray(num_elements);
+  for (int i = 0; i < num_elements; ++i) {
+    elements->set(i, *--parameters);
+  }
+  return isolate->factory()->NewJSArrayWithElements(
+      elements, FAST_ELEMENTS, num_elements, strength(language_mode));
+}
+
+
+RUNTIME_FUNCTION(Runtime_NewRestParam) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 4);
+  Object** parameters = reinterpret_cast<Object**>(args[0]);
+  CONVERT_SMI_ARG_CHECKED(num_params, 1);
+  CONVERT_SMI_ARG_CHECKED(rest_index, 2);
+  CONVERT_SMI_ARG_CHECKED(language_mode, 3);
+
+  return *NewRestParam(isolate, parameters, num_params, rest_index,
+                       static_cast<LanguageMode>(language_mode));
+}
+
+
+RUNTIME_FUNCTION(Runtime_NewRestParamSlow) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_SMI_ARG_CHECKED(rest_index, 0);
+  CONVERT_SMI_ARG_CHECKED(language_mode, 1);
+
+  JavaScriptFrameIterator it(isolate);
+
+  // Find the frame that holds the actual arguments passed to the function.
+  it.AdvanceToArgumentsFrame();
+  JavaScriptFrame* frame = it.frame();
+
+  int argument_count = frame->GetArgumentsLength();
+  Object** parameters = reinterpret_cast<Object**>(frame->GetParameterSlot(-1));
+
+  return *NewRestParam(isolate, parameters, argument_count, rest_index,
+                       static_cast<LanguageMode>(language_mode));
+}
+
+
 RUNTIME_FUNCTION(Runtime_NewClosure) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(SharedFunctionInfo, shared, 0);
   Handle<Context> context(isolate->context(), isolate);
   return *isolate->factory()->NewFunctionFromSharedFunctionInfo(shared, context,
                                                                 NOT_TENURED);
 }
 
 
@@ skipping 512 matching lines @@
 
   // Lookup in the initial Object.prototype object.
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       Object::GetProperty(isolate->initial_object_prototype(), key));
   return *result;
 }
 }  // namespace internal
 }  // namespace v8