Temporal dead zone behaviour for let bindings.

src/ia32/full-codegen-ia32.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 678 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);
+          __ mov(Operand(ebp, SlotOffset(slot)), result_register());
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
           __ mov(Operand(ebp, SlotOffset(slot)),
                  Immediate(isolate()->factory()->the_hole_value()));
-        } else if (function != NULL) {
-          VisitForAccumulatorValue(function);
-          __ mov(Operand(ebp, 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.
           __ mov(ebx, FieldOperand(esi, HeapObject::kMapOffset));
           __ cmp(ebx, isolate()->factory()->with_context_map());
           __ Check(not_equal, "Declaration in with context.");
           __ cmp(ebx, isolate()->factory()->catch_context_map());
           __ Check(not_equal, "Declaration in catch context.");
         }
-        if (mode == Variable::CONST) {
-          __ mov(ContextOperand(esi, slot->index()),
-                 Immediate(isolate()->factory()->the_hole_value()));
-          // No write barrier since the hole value is in old space.
-        } else if (function != NULL) {
+        if (function != NULL) {
           VisitForAccumulatorValue(function);
           __ mov(ContextOperand(esi, slot->index()), result_register());
           int offset = Context::SlotOffset(slot->index());
           __ mov(ebx, esi);
           __ RecordWrite(ebx, offset, result_register(), ecx);
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
+          __ mov(ContextOperand(esi, slot->index()),
+                 Immediate(isolate()->factory()->the_hole_value()));
+          // No write barrier since the hole value is in old space.
         }
         break;
 
       case Slot::LOOKUP: {
         __ push(esi);
         __ push(Immediate(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(Immediate(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.
         increment_stack_height(3);
-        if (mode == Variable::CONST) {
+        if (function != NULL) {
+          VisitForStackValue(function);
+        } else if (mode == Variable::CONST || mode == Variable::LET) {
           __ push(Immediate(isolate()->factory()->the_hole_value()));
           increment_stack_height();
-        } else if (function != NULL) {
-          VisitForStackValue(function);
         } else {
           __ push(Immediate(Smi::FromInt(0)));  // No initial value!
           increment_stack_height();
         }
         __ CallRuntime(Runtime::kDeclareContextSlot, 4);
         decrement_stack_height(4);
         break;
       }
     }
 
@@ skipping 528 matching lines @@
       // Constants may be the hole value if they have not been initialized.
       // Unhole them.
       Label done;
       MemOperand slot_operand = EmitSlotSearch(slot, eax);
       __ mov(eax, slot_operand);
       __ cmp(eax, isolate()->factory()->the_hole_value());
       __ j(not_equal, &done, Label::kNear);
       __ mov(eax, isolate()->factory()->undefined_value());
       __ bind(&done);
       context()->Plug(eax);
+    } 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, eax);
+      __ mov(eax, slot_operand);
+      __ cmp(eax, isolate()->factory()->the_hole_value());
+      __ j(not_equal, &done, Label::kNear);
+      __ push(Immediate(var->name()));
+      __ CallRuntime(Runtime::kThrowReferenceError, 1);
+      __ bind(&done);
+      context()->Plug(eax);
     } else {
       context()->Plug(slot);
     }
   }
 }
 
 
 void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
   Comment cmnt(masm_, "[ RegExpLiteral");
   Label materialized;
@@ skipping 577 matching lines @@
       case Slot::CONTEXT:
       case Slot::LOOKUP:
         __ push(eax);
         __ push(esi);
         __ push(Immediate(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.
+        __ mov(edx, Operand(ebp, SlotOffset(slot)));
+        __ cmp(edx, isolate()->factory()->the_hole_value());
+        __ j(not_equal, &assign);
+        __ push(Immediate(var->name()));
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ mov(Operand(ebp, SlotOffset(slot)), eax);
+        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, ecx);
+        // Check for an initialized let binding.
+        __ mov(edx, target);
+        __ cmp(edx, isolate()->factory()->the_hole_value());
+        __ j(not_equal, &assign, Label::kNear);
+        __ push(Immediate(var->name()));
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+        // Perform the assignment.
+        __ bind(&assign);
+        __ mov(target, eax);
+        // The value of the assignment is in eax. RecordWrite clobbers its
+        // register arguments.
+        __ mov(edx, eax);
+        int offset = Context::SlotOffset(slot->index());
+        __ RecordWrite(ecx, offset, edx, ebx);
+        break;
+      }
+
+      case Slot::LOOKUP:
+        // Call the runtime for the assignment.
+        __ push(eax);  // Value.
+        __ push(esi);  // Context.
+        __ push(Immediate(var->name()));
+        __ push(Immediate(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.
         __ mov(Operand(ebp, SlotOffset(slot)), eax);
         break;
@@ skipping 2461 matching lines @@
   __ add(Operand(edx), Immediate(masm_->CodeObject()));
   __ jmp(Operand(edx));
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32