Temporal dead zone behaviour for let bindings.

src/x64/full-codegen-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 653 matching lines @@
                                         FunctionLiteral* function) {
   Comment cmnt(masm_, "[ Declaration");
   ASSERT(variable != NULL);  // Must have been resolved.
   Slot* slot = variable->AsSlot();
   Property* prop = variable->AsProperty();
 
   if (slot != NULL) {
     switch (slot->type()) {
       case Slot::PARAMETER:
       case Slot::LOCAL:
-        if (mode == Variable::CONST) {
+        if (function != NULL) {
+          VisitForAccumulatorValue(function);
+          __ movq(Operand(rbp, SlotOffset(slot)), result_register());
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
           __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
           __ movq(Operand(rbp, SlotOffset(slot)), kScratchRegister);
-        } else if (function != NULL) {
-          VisitForAccumulatorValue(function);
-          __ movq(Operand(rbp, SlotOffset(slot)), result_register());
         }
         break;
 
       case Slot::CONTEXT:
         // We bypass the general EmitSlotSearch because we know more about
         // this specific context.
 
         // The variable in the decl always resides in the current function
         // context.
         ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
         if (FLAG_debug_code) {
           // Check that we're not inside a with or catch context.
           __ movq(rbx, FieldOperand(rsi, HeapObject::kMapOffset));
           __ CompareRoot(rbx, Heap::kWithContextMapRootIndex);
           __ Check(not_equal, "Declaration in with context.");
           __ CompareRoot(rbx, Heap::kCatchContextMapRootIndex);
           __ Check(not_equal, "Declaration in catch context.");
         }
-        if (mode == Variable::CONST) {
-          __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
-          __ movq(ContextOperand(rsi, slot->index()), kScratchRegister);
-          // No write barrier since the hole value is in old space.
-        } else if (function != NULL) {
+        if (function != NULL) {
           VisitForAccumulatorValue(function);
           __ movq(ContextOperand(rsi, slot->index()), result_register());
           int offset = Context::SlotOffset(slot->index());
           __ movq(rbx, rsi);
           __ RecordWrite(rbx, offset, result_register(), rcx);
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
+          __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
+          __ movq(ContextOperand(rsi, slot->index()), kScratchRegister);
+          // No write barrier since the hole value is in old space.
         }
         break;
 
       case Slot::LOOKUP: {
         __ push(rsi);
         __ Push(variable->name());
         // Declaration nodes are always introduced in one of two modes.
         ASSERT(mode == Variable::VAR ||
                mode == Variable::CONST ||
                mode == Variable::LET);
         PropertyAttributes attr = (mode == Variable::CONST) ? READ_ONLY : NONE;
         __ Push(Smi::FromInt(attr));
         // Push initial value, if any.
         // Note: For variables we must not push an initial value (such as
         // 'undefined') because we may have a (legal) redeclaration and we
         // must not destroy the current value.
-        if (mode == Variable::CONST) {
+        if (function != NULL) {
+          VisitForStackValue(function);
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
           __ PushRoot(Heap::kTheHoleValueRootIndex);
-        } else if (function != NULL) {
-          VisitForStackValue(function);
         } else {
           __ Push(Smi::FromInt(0));  // no initial value!
         }
         __ CallRuntime(Runtime::kDeclareContextSlot, 4);
         break;
       }
     }
 
   } else if (prop != NULL) {
     // A const declaration aliasing a parameter is an illegal redeclaration.
@@ skipping 530 matching lines @@
       // Constants may be the hole value if they have not been initialized.
       // Unhole them.
       Label done;
       MemOperand slot_operand = EmitSlotSearch(slot, rax);
       __ movq(rax, slot_operand);
       __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
       __ j(not_equal, &done, Label::kNear);
       __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
       __ bind(&done);
       context()->Plug(rax);
+    } else if (var->mode() == Variable::LET) {
+      // Let bindings may be the hole value if they have not been initialized.
+      // Throw a type error in this case.
+      Label done;
+      MemOperand slot_operand = EmitSlotSearch(slot, rax);
+      __ movq(rax, slot_operand);
+      __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
+      __ j(not_equal, &done, Label::kNear);
+      __ Push(var->name());
+      __ CallRuntime(Runtime::kThrowReferenceError, 1);
+      __ bind(&done);
+      context()->Plug(rax);
     } else {
       context()->Plug(slot);
     }
   }
 }
 
 
 void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
   Comment cmnt(masm_, "[ RegExpLiteral");
   Label materialized;
@@ skipping 509 matching lines @@
       case Slot::CONTEXT:
       case Slot::LOOKUP:
         __ push(rax);
         __ push(rsi);
         __ Push(var->name());
         __ CallRuntime(Runtime::kInitializeConstContextSlot, 3);
         break;
     }
     __ bind(&skip);
 
+  } else if (var->mode() == Variable::LET && op != Token::INIT_LET) {
+    // Perform the assignment for non-const variables.  Const assignments
+    // are simply skipped.
+    Slot* slot = var->AsSlot();
+    switch (slot->type()) {
+      case Slot::PARAMETER:
+      case Slot::LOCAL: {
+        Label assign;
+        // Check for an initialized let binding.
+        __ movq(rdx, Operand(rbp, SlotOffset(slot)));
+        __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
+        __ j(not_equal, &assign);
+        __ Push(var->name());
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ movq(Operand(rbp, SlotOffset(slot)), rax);
+        break;
+      }
+
+      case Slot::CONTEXT: {
+        // Let variables may be the hole value if they have not been
+        // initialized. Throw a type error in this case.
+        Label assign;
+        MemOperand target = EmitSlotSearch(slot, rcx);
+        // Check for an initialized let binding.
+        __ movq(rdx, target);
+        __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
+        __ j(not_equal, &assign, Label::kNear);
+        __ Push(var->name());
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ movq(target, rax);
+        // The value of the assignment is in eax. RecordWrite clobbers its
+        // register arguments.
+        __ movq(rdx, rax);
+        int offset = Context::SlotOffset(slot->index());
+        __ RecordWrite(rcx, offset, rdx, rbx);
+        break;
+      }
+
+      case Slot::LOOKUP:
+        // Call the runtime for the assignment.
+        __ push(rax);  // Value.
+        __ push(rsi);  // Context.
+        __ Push(var->name());
+        __ Push(Smi::FromInt(strict_mode_flag()));
+        __ CallRuntime(Runtime::kStoreContextSlot, 4);
+        break;
+    }
   } else if (var->mode() != Variable::CONST) {
     // Perform the assignment for non-const variables.  Const assignments
     // are simply skipped.
     Slot* slot = var->AsSlot();
     switch (slot->type()) {
       case Slot::PARAMETER:
       case Slot::LOCAL:
         // Perform the assignment.
         __ movq(Operand(rbp, SlotOffset(slot)), rax);
         break;
@@ skipping 2420 matching lines @@
   __ jmp(rdx);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64