Thread maybe-assigned through the bytecodes.

src/compiler/bytecode-graph-builder.cc

Index: src/compiler/bytecode-graph-builder.cc
diff --git a/src/compiler/bytecode-graph-builder.cc b/src/compiler/bytecode-graph-builder.cc
index d9f52a61b76ad03a381b3fbab4645ef6013da33c..4b2abad3dd3d23c579541519cb08314355494451 100644
--- a/src/compiler/bytecode-graph-builder.cc
+++ b/src/compiler/bytecode-graph-builder.cc
@@ -770,9 +770,6 @@ void BytecodeGraphBuilder::VisitStaDataPropertyInLiteral() {
 }
 
 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);
@@ -783,16 +780,31 @@ void BytecodeGraphBuilder::VisitLdaContextSlot() {
   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);

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

nit - you could pull out the shared code to a BuildLdaContextSlot helper
function which both this and VisitLdaContextSlot call to avoid duplicating code.

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

I thought about this and I'd prefer it this way because the duplication is quite
small and there is really no logic that needs to be kept in sync. I also suspect
a separate BuildLdaContextSlot would end up line-count positive.

+}
+
 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),