Partial revert of rest parameter desugaring.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 34813f8a08b606d8077180bce08a092906a726bc..821b9aad456219bfc6b89eeccf060c4e13b0cf02 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -841,6 +841,34 @@ void ArgumentsAccessStub::GenerateNewSloppySlow(MacroAssembler* masm) {
 }
 
 
+void RestParamAccessStub::GenerateNew(MacroAssembler* masm) {
+  // rsp[0]  : return address
+  // rsp[8]  : language mode
+  // rsp[16] : index of rest parameter
+  // rsp[24] : number of parameters
+  // rsp[32] : receiver displacement
+
+  // Check if the calling frame is an arguments adaptor frame.
+  Label runtime;
+  __ movp(rdx, Operand(rbp, StandardFrameConstants::kCallerFPOffset));
+  __ movp(rcx, Operand(rdx, StandardFrameConstants::kContextOffset));
+  __ Cmp(rcx, Smi::FromInt(StackFrame::ARGUMENTS_ADAPTOR));
+  __ j(not_equal, &runtime);
+
+  // Patch the arguments.length and the parameters pointer.
+  StackArgumentsAccessor args(rsp, 4, ARGUMENTS_DONT_CONTAIN_RECEIVER);
+  __ movp(rcx, Operand(rdx, ArgumentsAdaptorFrameConstants::kLengthOffset));
+  __ movp(args.GetArgumentOperand(1), rcx);
+  __ SmiToInteger64(rcx, rcx);
+  __ leap(rdx, Operand(rdx, rcx, times_pointer_size,
+                       StandardFrameConstants::kCallerSPOffset));
+  __ movp(args.GetArgumentOperand(0), rdx);
+
+  __ bind(&runtime);
+  __ TailCallRuntime(Runtime::kNewRestParam, 4, 1);
+}
+
+
 void LoadIndexedInterceptorStub::Generate(MacroAssembler* masm) {
   // Return address is on the stack.
   Label slow;