Reland of Thread maybe-assigned through the bytecodes.

src/compiler/bytecode-graph-builder.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/compiler/bytecode-graph-builder.h"
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/compilation-info.h"
 #include "src/compiler/compiler-source-position-table.h"
@@ skipping 752 matching lines @@
   int flags = bytecode_iterator().GetFlagOperand(2);
   VectorSlotPair feedback =
       CreateVectorSlotPair(bytecode_iterator().GetIndexOperand(3));
 
   const Operator* op = javascript()->StoreDataPropertyInLiteral(feedback);
   Node* node = NewNode(op, object, name, value, jsgraph()->Constant(flags));
   environment()->RecordAfterState(node, Environment::kAttachFrameState);
 }
 
 void BytecodeGraphBuilder::VisitLdaContextSlot() {
-  // TODO(mythria): immutable flag is also set to false. This information is not
-  // available in bytecode array. update this code when the implementation
-  // changes.
   const Operator* op = javascript()->LoadContext(
       bytecode_iterator().GetUnsignedImmediateOperand(2),
       bytecode_iterator().GetIndexOperand(1), false);
   Node* node = NewNode(op);
   Node* context =
       environment()->LookupRegister(bytecode_iterator().GetRegisterOperand(0));
   NodeProperties::ReplaceContextInput(node, context);
   environment()->BindAccumulator(node);
 }
 
+void BytecodeGraphBuilder::VisitLdaImmutableContextSlot() {
+  const Operator* op = javascript()->LoadContext(
+      bytecode_iterator().GetUnsignedImmediateOperand(2),
+      bytecode_iterator().GetIndexOperand(1), true);
+  Node* node = NewNode(op);
+  Node* context =
+      environment()->LookupRegister(bytecode_iterator().GetRegisterOperand(0));
+  NodeProperties::ReplaceContextInput(node, context);
+  environment()->BindAccumulator(node);
+}
+
 void BytecodeGraphBuilder::VisitLdaCurrentContextSlot() {
-  // TODO(mythria): immutable flag is also set to false. This information is not
-  // available in bytecode array. update this code when the implementation
-  // changes.
   const Operator* op = javascript()->LoadContext(
       0, bytecode_iterator().GetIndexOperand(0), false);
   Node* node = NewNode(op);
   environment()->BindAccumulator(node);
 }
+
+void BytecodeGraphBuilder::VisitLdaImmutableCurrentContextSlot() {
+  const Operator* op = javascript()->LoadContext(
+      0, bytecode_iterator().GetIndexOperand(0), true);
+  Node* node = NewNode(op);
+  environment()->BindAccumulator(node);
+}
 
 void BytecodeGraphBuilder::VisitStaContextSlot() {
   const Operator* op = javascript()->StoreContext(
       bytecode_iterator().GetUnsignedImmediateOperand(2),
       bytecode_iterator().GetIndexOperand(1));
   Node* value = environment()->LookupAccumulator();
   Node* node = NewNode(op, value);
   Node* context =
       environment()->LookupRegister(bytecode_iterator().GetRegisterOperand(0));
   NodeProperties::ReplaceContextInput(node, context);
@@ skipping 1510 matching lines @@
         it->source_position().ScriptOffset(), start_position_.InliningId()));
     it->Advance();
   } else {
     DCHECK_GT(it->code_offset(), offset);
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8