[turbofan] Introduce JSCallForwardVarargs operator.

src/x64/interface-descriptors-x64.cc

 // Copyright 2012 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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/interface-descriptors.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 157 matching lines @@
 
 
 void CallTrampolineDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   // rax : number of arguments
   // rdi : the target to call
   Register registers[] = {rdi, rax};
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  // rcx : start index (to support rest parameters)
+  // rdi : the target to call
+  Register registers[] = {rdi, rcx};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
 
 void ConstructStubDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   // rax : number of arguments
   // rdx : the new target
   // rdi : the target to call
   // rbx : allocation site or undefined
   Register registers[] = {rdi, rdx, rax, rbx};
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
@@ skipping 217 matching lines @@
       rbx,  // the JSGeneratorObject to resume
       rdx   // the resume mode (tagged)
   };
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64