Thread maybe-assigned through the bytecodes.

src/interpreter/interpreter.cc

 // Copyright 2015 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.
 
 #include "src/interpreter/interpreter.h"
 
 #include <fstream>
 #include <memory>
 
 #include "src/ast/prettyprinter.h"
@@ skipping 538 matching lines @@
   Node* reg_index = __ BytecodeOperandReg(0);
   Node* context = __ LoadRegister(reg_index);
   Node* slot_index = __ BytecodeOperandIdx(1);
   Node* depth = __ BytecodeOperandUImm(2);
   Node* slot_context = __ GetContextAtDepth(context, depth);
   Node* result = __ LoadContextElement(slot_context, slot_index);
   __ SetAccumulator(result);
   __ Dispatch();
 }
 
+// LdaImmutableContextSlot <context> <slot_index> <depth>
+//
+// Load the object in |slot_index| of the context at |depth| in the context
+// chain starting at |context| into the accumulator.
+void Interpreter::DoLdaImmutableContextSlot(InterpreterAssembler* assembler) {
+  DoLdaContextSlot(assembler);

[rmcilroy, 2017/02/07 14:02:14]

Could you add a TODO for Danno to share the machine code for the bytecode
handlers for both this and DoLdaContextSlot

+Danno - FYI.

[Jarin, 2017/02/07 14:31:05]

Done.

+}
+
 // LdaCurrentContextSlot <slot_index>
 //
 // Load the object in |slot_index| of the current context into the accumulator.
 void Interpreter::DoLdaCurrentContextSlot(InterpreterAssembler* assembler) {
   Node* slot_index = __ BytecodeOperandIdx(0);
   Node* slot_context = __ GetContext();
   Node* result = __ LoadContextElement(slot_context, slot_index);
   __ SetAccumulator(result);
   __ Dispatch();
 }
 
+// LdaImmutableCurrentContextSlot <slot_index>
+//
+// Load the object in |slot_index| of the current context into the accumulator.
+void Interpreter::DoLdaImmutableCurrentContextSlot(
+    InterpreterAssembler* assembler) {
+  DoLdaCurrentContextSlot(assembler);
+}
+
 // StaContextSlot <context> <slot_index> <depth>
 //
 // Stores the object in the accumulator into |slot_index| of the context at
 // |depth| in the context chain starting at |context|.
 void Interpreter::DoStaContextSlot(InterpreterAssembler* assembler) {
   Node* value = __ GetAccumulator();
   Node* reg_index = __ BytecodeOperandReg(0);
   Node* context = __ LoadRegister(reg_index);
   Node* slot_index = __ BytecodeOperandIdx(1);
   Node* depth = __ BytecodeOperandUImm(2);
@@ skipping 2731 matching lines @@
   __ StoreObjectField(generator, JSGeneratorObject::kContinuationOffset,
       __ SmiTag(new_state));
   __ SetAccumulator(old_state);
 
   __ Dispatch();
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8