Remove the fcontext field from all contexts.

src/x64/code-stubs-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 114 matching lines @@
   __ movq(rcx, Operand(rsp, 1 * kPointerSize));
 
   // Setup the object header.
   __ LoadRoot(kScratchRegister, Heap::kFunctionContextMapRootIndex);
   __ movq(FieldOperand(rax, HeapObject::kMapOffset), kScratchRegister);
   __ Move(FieldOperand(rax, FixedArray::kLengthOffset), Smi::FromInt(length));
 
   // Setup the fixed slots.
   __ Set(rbx, 0);  // Set to NULL.
   __ movq(Operand(rax, Context::SlotOffset(Context::CLOSURE_INDEX)), rcx);
-  __ movq(Operand(rax, Context::SlotOffset(Context::FCONTEXT_INDEX)), rax);
   __ movq(Operand(rax, Context::SlotOffset(Context::PREVIOUS_INDEX)), rsi);
   __ movq(Operand(rax, Context::SlotOffset(Context::EXTENSION_INDEX)), rbx);
 
   // Copy the global object from the previous context.
   __ movq(rbx, Operand(rsi, Context::SlotOffset(Context::GLOBAL_INDEX)));
   __ movq(Operand(rax, Context::SlotOffset(Context::GLOBAL_INDEX)), rbx);
 
   // Initialize the rest of the slots to undefined.
   __ LoadRoot(rbx, Heap::kUndefinedValueRootIndex);
   for (int i = Context::MIN_CONTEXT_SLOTS; i < length; i++) {
@@ skipping 5194 matching lines @@
   __ Drop(1);
   __ ret(2 * kPointerSize);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64