[ignition] Only initialize [[HomeObject]] for class constructors if needed

src/interpreter/bytecode-generator.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/bytecode-generator.h"
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/builtins/builtins-constructor.h"
 #include "src/code-stubs.h"
@@ skipping 1393 matching lines @@
 
 void BytecodeGenerator::VisitFunctionLiteral(FunctionLiteral* expr) {
   uint8_t flags = CreateClosureFlags::Encode(expr->pretenure(),
                                              scope()->is_function_scope());
   size_t entry = builder()->AllocateConstantPoolEntry();
   builder()->CreateClosure(entry, flags);
   function_literals_.push_back(std::make_pair(expr, entry));
 }
 
 void BytecodeGenerator::VisitClassLiteral(ClassLiteral* expr) {
-  VisitClassLiteralForRuntimeDefinition(expr);
+  Register constructor = register_allocator()->NewRegister();
+  VisitForRegisterValue(expr->constructor(), constructor);

[rmcilroy, 2017/01/04 09:55:59]

nit - you can just do:
Register constructor = VisitForRegisterValue(expr->constructor());

[adamk, 2017/01/04 17:57:03]

Ah, nice.

+  Register prototype = register_allocator()->NewRegister();

[rmcilroy, 2017/01/04 09:55:59]

nit - you could save a register if you allocate this after the runtime call
block and move the StoreAccumulatorInRegister(prototype) out of that block.

[adamk, 2017/01/04 17:57:03]

Done.

+  {
+    RegisterAllocationScope register_scope(this);
+    RegisterList args = register_allocator()->NewRegisterList(4);
+    VisitForAccumulatorValueOrTheHole(expr->extends());
+    builder()
+        ->StoreAccumulatorInRegister(args[0])
+        .MoveRegister(constructor, args[1])
+        .LoadLiteral(Smi::FromInt(expr->start_position()))
+        .StoreAccumulatorInRegister(args[2])
+        .LoadLiteral(Smi::FromInt(expr->end_position()))
+        .StoreAccumulatorInRegister(args[3])
+        .CallRuntime(Runtime::kDefineClass, args)
+        .StoreAccumulatorInRegister(prototype);
+  }
 
-  // Load the "prototype" from the constructor.
-  Register literal = register_allocator()->NewRegister();
-  Register prototype = register_allocator()->NewRegister();
-  FeedbackVectorSlot slot = expr->PrototypeSlot();
-  builder()
-      ->StoreAccumulatorInRegister(literal)
-      .LoadNamedProperty(literal, prototype_string(), feedback_index(slot))
-      .StoreAccumulatorInRegister(prototype);
+  if (FunctionLiteral::NeedsHomeObject(expr->constructor())) {
+    // prototype is already in the accumulator

[rmcilroy, 2017/01/04 09:55:59]

nit - fullstop and capital letter for comments.

[adamk, 2017/01/04 17:57:03]

Done.

+    builder()->StoreNamedProperty(constructor, home_object_symbol(),
+                                  feedback_index(expr->HomeObjectSlot()),
+                                  language_mode());
+  }
 
-  VisitClassLiteralProperties(expr, literal, prototype);
-  BuildClassLiteralNameProperty(expr, literal);
-  builder()->CallRuntime(Runtime::kToFastProperties, literal);
+  VisitClassLiteralProperties(expr, constructor, prototype);
+  BuildClassLiteralNameProperty(expr, constructor);
+  builder()->CallRuntime(Runtime::kToFastProperties, constructor);
   // Assign to class variable.
   if (expr->class_variable_proxy() != nullptr) {
     VariableProxy* proxy = expr->class_variable_proxy();
     FeedbackVectorSlot slot = expr->NeedsProxySlot()
                                   ? expr->ProxySlot()
                                   : FeedbackVectorSlot::Invalid();
     BuildVariableAssignment(proxy->var(), Token::INIT, slot,
                             HoleCheckMode::kElided);
   }
 }
 
-void BytecodeGenerator::VisitClassLiteralForRuntimeDefinition(
-    ClassLiteral* expr) {
-  RegisterAllocationScope register_scope(this);
-  RegisterList args = register_allocator()->NewRegisterList(4);
-  VisitForAccumulatorValueOrTheHole(expr->extends());
-  builder()->StoreAccumulatorInRegister(args[0]);
-  VisitForRegisterValue(expr->constructor(), args[1]);
-  builder()
-      ->LoadLiteral(Smi::FromInt(expr->start_position()))
-      .StoreAccumulatorInRegister(args[2])
-      .LoadLiteral(Smi::FromInt(expr->end_position()))
-      .StoreAccumulatorInRegister(args[3])
-      .CallRuntime(Runtime::kDefineClass, args);
-}
-
 void BytecodeGenerator::VisitClassLiteralProperties(ClassLiteral* expr,
-                                                    Register literal,
+                                                    Register constructor,
                                                     Register prototype) {
   RegisterAllocationScope register_scope(this);
   RegisterList args = register_allocator()->NewRegisterList(4);
   Register receiver = args[0], key = args[1], value = args[2], attr = args[3];
 
   bool attr_assigned = false;
   Register old_receiver = Register::invalid_value();
 
   // Create nodes to store method values into the literal.
   for (int i = 0; i < expr->properties()->length(); i++) {
     ClassLiteral::Property* property = expr->properties()->at(i);
 
     // Set-up receiver.
-    Register new_receiver = property->is_static() ? literal : prototype;
+    Register new_receiver = property->is_static() ? constructor : prototype;
     if (new_receiver != old_receiver) {
       builder()->MoveRegister(new_receiver, receiver);
       old_receiver = new_receiver;
     }
 
     VisitForAccumulatorValue(property->key());
     builder()->ConvertAccumulatorToName(key);
 
     if (property->is_static() && property->is_computed_name()) {
       // The static prototype property is read only. We handle the non computed
@@ skipping 1829 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8