[runtime] Optimize and unify rest parameters.

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 891b5201a305978412ad9be8fbf3e917a7f9c963..f3b1c21aca6c253e0e3367b9757abe6e37902f46 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -254,21 +254,12 @@ void FullCodeGenerator::Generate() {
   Variable* rest_param = scope()->rest_parameter(&rest_index);
   if (rest_param) {
     Comment cmnt(masm_, "[ Allocate rest parameter array");
-
-    int num_parameters = info->scope()->num_parameters();
-    int offset = num_parameters * kPointerSize;
-
-    __ Move(RestParamAccessDescriptor::parameter_count(),
-            Smi::FromInt(num_parameters));
-    __ leap(RestParamAccessDescriptor::parameter_pointer(),
-            Operand(rbp, StandardFrameConstants::kCallerSPOffset + offset));
-    __ Move(RestParamAccessDescriptor::rest_parameter_index(),
-            Smi::FromInt(rest_index));
-    function_in_register = false;
-
-    RestParamAccessStub stub(isolate());
+    if (!function_in_register) {
+      __ movp(rdi, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
+    }
+    FastNewRestParameterStub stub(isolate());
     __ CallStub(&stub);
-
+    function_in_register = false;
     SetVar(rest_param, rax, rbx, rdx);
   }