[es6] Tail calls support.

src/x64/code-stubs-x64.cc

 // Copyright 2013 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/bootstrapper.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
 #include "src/ic/handler-compiler.h"
@@ skipping 1984 matching lines @@
   // convincing us that we have a monomorphic JSFunction.
   __ JumpIfSmi(rdi, &extra_checks_or_miss);
 
   // Increment the call count for monomorphic function calls.
   __ SmiAddConstant(FieldOperand(rbx, rdx, times_pointer_size,
                                  FixedArray::kHeaderSize + kPointerSize),
                     Smi::FromInt(CallICNexus::kCallCountIncrement));
 
   __ bind(&call_function);
   __ Set(rax, argc);
-  __ Jump(masm->isolate()->builtins()->CallFunction(convert_mode()),
-          RelocInfo::CODE_TARGET);
+  Handle<Code> call_function_builtin =
+      tail_call_mode() == TailCallMode::kDisallow
+          ? masm->isolate()->builtins()->CallFunction(convert_mode())
+          : masm->isolate()->builtins()->TailCallFunction(convert_mode());
+  __ Jump(call_function_builtin, RelocInfo::CODE_TARGET);
 
   __ bind(&extra_checks_or_miss);
   Label uninitialized, miss, not_allocation_site;
 
   __ Cmp(rcx, TypeFeedbackVector::MegamorphicSentinel(isolate));
   __ j(equal, &call);
 
   // Check if we have an allocation site.
   __ CompareRoot(FieldOperand(rcx, HeapObject::kMapOffset),
                  Heap::kAllocationSiteMapRootIndex);
@@ skipping 3406 matching lines @@
                            kStackSpace, nullptr, return_value_operand, NULL);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64