Block scoped const variables.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index eda2e55781fbb574ac547f1b904808f7c5c5e615..1c00a9bfc40cb0af8920a29c64693220ef3dc5c2 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -254,7 +254,10 @@ void FullCodeGenerator::Generate(CompilationInfo* info) {
       // constant.
       if (scope()->is_function_scope() && scope()->function() != NULL) {
         int ignored = 0;
-        EmitDeclaration(scope()->function(), CONST, NULL, &ignored);
+        VariableProxy* proxy = scope()->function();
+        ASSERT(proxy->var()->mode() == CONST ||
+               proxy->var()->mode() == CONST_HARMONY);
+        EmitDeclaration(proxy, proxy->var()->mode(), NULL, &ignored);
       }
       VisitDeclarations(scope()->declarations());
     }
@@ -684,6 +687,8 @@ void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
   // 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);
@@ -695,7 +700,7 @@ void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
         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);
@@ -728,7 +733,7 @@ void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
                                   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);
@@ -741,9 +746,13 @@ void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
       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
@@ -751,7 +760,7 @@ void FullCodeGenerator::EmitDeclaration(VariableProxy* proxy,
       // 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.
@@ -1182,12 +1191,14 @@ void FullCodeGenerator::EmitDynamicLookupFastCase(Variable* var,
   } 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);
       }
@@ -1221,7 +1232,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
     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.
@@ -1229,10 +1240,14 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
         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);
@@ -1854,8 +1869,9 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
       }
     }
 
-  } 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) {