Reland of Thread maybe-assigned through the bytecodes.

test/unittests/interpreter/bytecode-array-builder-unittest.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/interpreter/bytecode-array-builder.h"
 #include "src/interpreter/bytecode-array-iterator.h"
 #include "src/interpreter/bytecode-label.h"
 #include "src/interpreter/bytecode-register-allocator.h"
@@ skipping 68 matching lines @@
   // Emit global load / store operations.
   Handle<String> name = factory->NewStringFromStaticChars("var_name");
   builder.LoadGlobal(name, 1, TypeofMode::NOT_INSIDE_TYPEOF)
       .LoadGlobal(name, 1, TypeofMode::INSIDE_TYPEOF)
       .StoreGlobal(name, 1, LanguageMode::SLOPPY)
       .StoreGlobal(name, 1, LanguageMode::STRICT);
 
   // Emit context operations.
   builder.PushContext(reg)
       .PopContext(reg)
-      .LoadContextSlot(reg, 1, 0)
-      .StoreContextSlot(reg, 1, 0);
+      .LoadContextSlot(reg, 1, 0, BytecodeArrayBuilder::kMutableSlot)
+      .StoreContextSlot(reg, 1, 0)
+      .LoadContextSlot(reg, 2, 0, BytecodeArrayBuilder::kImmutableSlot)
+      .StoreContextSlot(reg, 3, 0);
 
   // Emit context operations which operate on the local context.
-  builder.LoadContextSlot(Register::current_context(), 1, 0)
-      .StoreContextSlot(Register::current_context(), 1, 0);
+  builder
+      .LoadContextSlot(Register::current_context(), 1, 0,
+                       BytecodeArrayBuilder::kMutableSlot)
+      .StoreContextSlot(Register::current_context(), 1, 0)
+      .LoadContextSlot(Register::current_context(), 2, 0,
+                       BytecodeArrayBuilder::kImmutableSlot)
+      .StoreContextSlot(Register::current_context(), 3, 0);
 
   // Emit load / store property operations.
   builder.LoadNamedProperty(reg, name, 0)
       .LoadKeyedProperty(reg, 0)
       .StoreNamedProperty(reg, name, 0, LanguageMode::SLOPPY)
       .StoreKeyedProperty(reg, reg, 0, LanguageMode::SLOPPY)
       .StoreNamedProperty(reg, name, 0, LanguageMode::STRICT)
       .StoreKeyedProperty(reg, reg, 0, LanguageMode::STRICT);
 
   // Emit load / store lookup slots.
@@ skipping 215 matching lines @@
       .LoadKeyedProperty(reg, 2056)
       .StoreNamedProperty(reg, wide_name, 0, LanguageMode::SLOPPY)
       .StoreKeyedProperty(reg, reg, 2056, LanguageMode::SLOPPY)
       .StoreNamedProperty(reg, wide_name, 0, LanguageMode::STRICT)
       .StoreKeyedProperty(reg, reg, 2056, LanguageMode::STRICT);
 
   builder.StoreDataPropertyInLiteral(reg, reg,
                                      DataPropertyInLiteralFlag::kNoFlags, 0);
 
   // Emit wide context operations.
-  builder.LoadContextSlot(reg, 1024, 0).StoreContextSlot(reg, 1024, 0);
+  builder.LoadContextSlot(reg, 1024, 0, BytecodeArrayBuilder::kMutableSlot)
+      .StoreContextSlot(reg, 1024, 0);
 
   // Emit wide load / store lookup slots.
   builder.LoadLookupSlot(wide_name, TypeofMode::NOT_INSIDE_TYPEOF)
       .LoadLookupSlot(wide_name, TypeofMode::INSIDE_TYPEOF)
       .StoreLookupSlot(wide_name, LanguageMode::SLOPPY)
       .StoreLookupSlot(wide_name, LanguageMode::STRICT);
 
   // CreateClosureWide
   builder.CreateClosure(1000, 321, NOT_TENURED);
 
@@ skipping 415 matching lines @@
     iterator.Advance();
   }
   CHECK_EQ(iterator.current_bytecode(), Bytecode::kReturn);
   iterator.Advance();
   CHECK(iterator.done());
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8