new classes: special construct stub for derived classs and TDZ for `this`.

src/ia32/full-codegen-ia32.cc

 // Copyright 2012 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"
 
 #if V8_TARGET_ARCH_IA32
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 1442 matching lines @@
         //   if (false) { const x; }; var y = x;
         //
         // The condition on the declaration scopes is a conservative check for
         // nested functions that access a binding and are called before the
         // binding is initialized:
         //   function() { f(); let x = 1; function f() { x = 2; } }
         //
         bool skip_init_check;
         if (var->scope()->DeclarationScope() != scope()->DeclarationScope()) {
           skip_init_check = false;
+        } else if (var->is_this()) {

[rossberg, 2015/02/02 16:32:37]

Does this now affect every use of 'this'? Can we limit the check to actual
constructors?

[Dmitry Lomov (no reviews), 2015/02/03 15:47:04]

No, this only happens if var->binding_needs_init() and `this` does not need
intitalization outside of subclass constructors. Added an assert.

+          // TODO(dslomov): implement 'this' hole check elimination.
+          skip_init_check = false;
         } else {
           // Check that we always have valid source position.
           DCHECK(var->initializer_position() != RelocInfo::kNoPosition);
           DCHECK(proxy->position() != RelocInfo::kNoPosition);
           skip_init_check = var->mode() != CONST_LEGACY &&
               var->initializer_position() < proxy->position();
         }
 
         if (!skip_init_check) {
           // Let and const need a read barrier.
@@ skipping 1659 matching lines @@
   PrepareForBailoutForId(expr->ReturnId(), TOS_REG);
   context()->Plug(eax);
 }
 
 
 void FullCodeGenerator::EmitSuperConstructorCall(Call* expr) {
   SuperReference* super_ref = expr->expression()->AsSuperReference();
   EmitLoadSuperConstructor(super_ref);
   __ push(result_register());
 
+  Variable* this_var = super_ref->this_var()->var();
+  GetVar(eax, this_var);
+  __ cmp(eax, isolate()->factory()->the_hole_value());
+  Label uninitialized_this;
+  __ j(equal, &uninitialized_this);
+  __ push(Immediate(this_var->name()));
+  __ CallRuntime(Runtime::kThrowReferenceError, 1);
+  __ bind(&uninitialized_this);
+
   // Push the arguments ("left-to-right") on the stack.
   ZoneList<Expression*>* args = expr->arguments();
   int arg_count = args->length();
   for (int i = 0; i < arg_count; i++) {
     VisitForStackValue(args->at(i));
   }
 
   // Call the construct call builtin that handles allocation and
   // constructor invocation.
   SetSourcePosition(expr->position());
@@ skipping 14 matching lines @@
 
   __ LoadHeapObject(ebx, FeedbackVector());
   __ mov(edx, Immediate(SmiFromSlot(expr->CallFeedbackSlot())));
 
   // TODO(dslomov): use a different stub and propagate new.target.
   CallConstructStub stub(isolate(), RECORD_CONSTRUCTOR_TARGET);
   __ call(stub.GetCode(), RelocInfo::CONSTRUCT_CALL);
 
   RecordJSReturnSite(expr);
 
-  // TODO(dslomov): implement TDZ for `this`.
-  EmitVariableAssignment(super_ref->this_var()->var(), Token::ASSIGN);
+  EmitVariableAssignment(this_var, Token::INIT_CONST);
   context()->Plug(eax);
 }
 
 
 void FullCodeGenerator::EmitIsSmi(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   DCHECK(args->length() == 1);
 
   VisitForAccumulatorValue(args->at(0));
 
@@ skipping 2094 matching lines @@
   DCHECK_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32