Block scoped const variables.

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 666 matching lines @@
 
 
 void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
                                         VariableMode mode,
                                         FunctionLiteral* function,
                                         int* global_count) {
   // If it was not possible to allocate the variable at compile time, we
   // need to "declare" it at runtime to make sure it actually exists in the
   // local context.
   Variable* variable = proxy->var();
+  bool binding_needs_init =
+      mode == CONST || mode == CONST_HARMONY || mode == LET;
   switch (variable->location()) {
     case Variable::UNALLOCATED:
       ++(*global_count);
       break;
 
     case Variable::PARAMETER:
     case Variable::LOCAL:
       if (function != NULL) {
         Comment cmnt(masm_, "[ Declaration");
         VisitForAccumulatorValue(function);
         __ movq(StackOperand(variable), result_register());
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         Comment cmnt(masm_, "[ Declaration");
         __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
         __ movq(StackOperand(variable), kScratchRegister);
       }
       break;
 
     case Variable::CONTEXT:
       // The variable in the decl always resides in the current function
       // context.
       ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
@@ skipping 12 matching lines @@
         int offset = Context::SlotOffset(variable->index());
         // We know that we have written a function, which is not a smi.
         __ RecordWriteContextSlot(rsi,
                                   offset,
                                   result_register(),
                                   rcx,
                                   kDontSaveFPRegs,
                                   EMIT_REMEMBERED_SET,
                                   OMIT_SMI_CHECK);
         PrepareForBailoutForId(proxy->id(), NO_REGISTERS);
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         Comment cmnt(masm_, "[ Declaration");
         __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
         __ movq(ContextOperand(rsi, variable->index()), kScratchRegister);
         // No write barrier since the hole value is in old space.
         PrepareForBailoutForId(proxy->id(), NO_REGISTERS);
       }
       break;
 
     case Variable::LOOKUP: {
       Comment cmnt(masm_, "[ Declaration");
       __ push(rsi);
       __ Push(variable->name());
-      // Declaration nodes are always introduced in one of three modes.
-      ASSERT(mode == VAR || mode == CONST || mode == LET);
-      PropertyAttributes attr = (mode == CONST) ? READ_ONLY : NONE;
+      // Declaration nodes are always introduced in one of four modes.
+      ASSERT(mode == VAR ||
+             mode == CONST ||
+             mode == CONST_HARMONY ||
+             mode == LET);
+      PropertyAttributes attr =
+          (mode == CONST || mode == CONST_HARMONY) ? 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 (function != NULL) {
         VisitForStackValue(function);
-      } else if (mode == CONST || mode == LET) {
+      } else if (binding_needs_init) {
         __ PushRoot(Heap::kTheHoleValueRootIndex);
       } else {
         __ Push(Smi::FromInt(0));  // Indicates no initial value.
       }
       __ CallRuntime(Runtime::kDeclareContextSlot, 4);
       break;
     }
   }
 }
 
@@ skipping 410 matching lines @@
   // eval-introduced variables.  Eval is used a lot without
   // introducing variables.  In those cases, we do not want to
   // perform a runtime call for all variables in the scope
   // containing the eval.
   if (var->mode() == DYNAMIC_GLOBAL) {
     EmitLoadGlobalCheckExtensions(var, typeof_state, slow);
     __ jmp(done);
   } else if (var->mode() == DYNAMIC_LOCAL) {
     Variable* local = var->local_if_not_shadowed();
     __ movq(rax, ContextSlotOperandCheckExtensions(local, slow));
-    if (local->mode() == CONST || local->mode() == LET) {
+    if (local->mode() == CONST ||
+        local->mode() == CONST_HARMONY ||
+        local->mode() == LET) {
       __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
       __ j(not_equal, done);
       if (local->mode() == CONST) {
         __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
-      } else {  // LET
+      } else {  // LET || CONST_HARMONY
         __ Push(var->name());
         __ CallRuntime(Runtime::kThrowReferenceError, 1);
       }
     }
     __ jmp(done);
   }
 }
 
 
 void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
@@ skipping 13 matching lines @@
       Handle<Code> ic = isolate()->builtins()->LoadIC_Initialize();
       __ call(ic, RelocInfo::CODE_TARGET_CONTEXT);
       context()->Plug(rax);
       break;
     }
 
     case Variable::PARAMETER:
     case Variable::LOCAL:
     case Variable::CONTEXT: {
       Comment cmnt(masm_, var->IsContextSlot() ? "Context slot" : "Stack slot");
-      if (var->mode() != LET && var->mode() != CONST) {
+      if (!var->binding_needs_init()) {
         context()->Plug(var);
       } else {
         // Let and const need a read barrier.
         Label done;
         GetVar(rax, var);
         __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
         __ j(not_equal, &done, Label::kNear);
-        if (var->mode() == LET) {
+        if (var->mode() == LET || var->mode() == CONST_HARMONY) {
+          // Throw a reference error when using an uninitialized let/const
+          // binding in harmony mode.
           __ Push(var->name());
           __ CallRuntime(Runtime::kThrowReferenceError, 1);
-        } else {  // CONST
+        } else {
+          // Uninitalized const bindings outside of harmony mode are unholed.
+          ASSERT(var->mode() == CONST);
           __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
         }
         __ bind(&done);
         context()->Plug(rax);
       }
       break;
     }
 
     case Variable::LOOKUP: {
       Label done, slow;
@@ skipping 552 matching lines @@
       __ CallRuntime(Runtime::kThrowReferenceError, 1);
       __ bind(&assign);
       __ movq(location, rax);
       if (var->IsContextSlot()) {
         __ movq(rdx, rax);
         __ RecordWriteContextSlot(
             rcx, Context::SlotOffset(var->index()), rdx, rbx, kDontSaveFPRegs);
       }
     }
 
-  } else if (var->mode() != CONST) {
-    // Assignment to var or initializing assignment to let.
+  } else if (!var->is_const_mode() || op == Token::INIT_CONST_HARMONY) {
+    // Assignment to var or initializing assignment to let/const
+    // in harmony mode.
     if (var->IsStackAllocated() || var->IsContextSlot()) {
       MemOperand location = VarOperand(var, rcx);
       if (FLAG_debug_code && op == Token::INIT_LET) {
         // Check for an uninitialized let binding.
         __ movq(rdx, location);
         __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
         __ Check(equal, "Let binding re-initialization.");
       }
       // Perform the assignment.
       __ movq(location, rax);
@@ skipping 2367 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64