Use Variable::binding_needs_init() to determine hole initialization

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 67c8ecb908ccd3d4b50c67e9b4581889f4489b00..593029465fe9e0b4cabf23909a72fee982a11fba 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -719,13 +719,8 @@ void FullCodeGenerator::EmitDebugCheckDeclarationContext(Variable* variable) {
 
 void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
-  // 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.
   VariableProxy* proxy = declaration->proxy();
-  VariableMode mode = declaration->mode();
   Variable* variable = proxy->var();
-  bool hole_init = mode == LET || mode == CONST;
   switch (variable->location()) {
     case VariableLocation::GLOBAL:
     case VariableLocation::UNALLOCATED: {
@@ -738,7 +733,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (hole_init) {
+      if (variable->binding_needs_init()) {
         Comment cmnt(masm_, "[ VariableDeclaration");
         __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
         __ movp(StackOperand(variable), kScratchRegister);
@@ -746,7 +741,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
       break;
 
     case VariableLocation::CONTEXT:
-      if (hole_init) {
+      if (variable->binding_needs_init()) {
         Comment cmnt(masm_, "[ VariableDeclaration");
         EmitDebugCheckDeclarationContext(variable);
         __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
@@ -758,8 +753,8 @@ void FullCodeGenerator::VisitVariableDeclaration(
 
     case VariableLocation::LOOKUP: {
       Comment cmnt(masm_, "[ VariableDeclaration");
-      DCHECK_EQ(VAR, mode);
-      DCHECK(!hole_init);
+      DCHECK_EQ(VAR, variable->mode());
+      DCHECK(!variable->binding_needs_init());
       __ Push(variable->name());
       __ CallRuntime(Runtime::kDeclareEvalVar);
       PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
@@ -1223,13 +1218,14 @@ void FullCodeGenerator::EmitDynamicLookupFastCase(VariableProxy* proxy,
   } else if (var->mode() == DYNAMIC_LOCAL) {
     Variable* local = var->local_if_not_shadowed();
     __ movp(rax, ContextSlotOperandCheckExtensions(local, slow));
-    if (local->mode() == LET || local->mode() == CONST) {
+    if (local->binding_needs_init()) {
       __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
       __ j(not_equal, done);
       __ Push(var->name());
       __ CallRuntime(Runtime::kThrowReferenceError);
+    } else {

[adamk, 2016/08/03 23:38:55]

We previously always emitted the jmp below, even when it was unreachable due to
the Throw above.

+      __ jmp(done);
     }
-    __ jmp(done);
   }
 }
 
@@ -1272,17 +1268,15 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context slot"
                                                : "[ Stack slot");
       if (NeedsHoleCheckForLoad(proxy)) {
-        // Let and const need a read barrier.
+        // Throw a reference error when using an uninitialized let/const
+        // binding in harmony mode.
+        DCHECK(IsLexicalVariableMode(var->mode()));
         Label done;
         GetVar(rax, var);
         __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
         __ j(not_equal, &done, Label::kNear);
-        if (var->mode() == LET || var->mode() == CONST) {

[adamk, 2016/08/03 23:38:55]

There should be no way for us to get into this block if we're not either LET or
CONST.

-          // Throw a reference error when using an uninitialized let/const
-          // binding in harmony mode.
-          __ Push(var->name());
-          __ CallRuntime(Runtime::kThrowReferenceError);
-        }
+        __ Push(var->name());
+        __ CallRuntime(Runtime::kThrowReferenceError);
         __ bind(&done);
         context()->Plug(rax);
         break;
@@ -2064,33 +2058,26 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     EmitLoadStoreICSlot(slot);
     CallStoreIC();
 
-  } else if (var->mode() == LET && op != Token::INIT) {
-    // Non-initializing assignment to let variable needs a write barrier.
+  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
     DCHECK(!var->IsLookupSlot());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label assign;
     MemOperand location = VarOperand(var, rcx);
-    __ movp(rdx, location);
-    __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
-    __ j(not_equal, &assign, Label::kNear);
-    __ Push(var->name());
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&assign);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
-  } else if (var->mode() == CONST && op != Token::INIT) {
-    // Assignment to const variable needs a write barrier.
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label const_error;
-    MemOperand location = VarOperand(var, rcx);
-    __ movp(rdx, location);
-    __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
-    __ j(not_equal, &const_error, Label::kNear);
-    __ Push(var->name());
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&const_error);
-    __ CallRuntime(Runtime::kThrowConstAssignError);
+    // Perform an initialization check for lexically declared variables.
+    if (var->binding_needs_init()) {
+      Label assign;
+      __ movp(rdx, location);
+      __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
+      __ j(not_equal, &assign, Label::kNear);
+      __ Push(var->name());
+      __ CallRuntime(Runtime::kThrowReferenceError);
+      __ bind(&assign);
+    }
+    if (var->mode() == CONST) {
+      // Assignment to const is exception in all modes.
+      __ CallRuntime(Runtime::kThrowConstAssignError);
+    } else {
+      EmitStoreToStackLocalOrContextSlot(var, location);
+    }
 
   } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
     // Initializing assignment to const {this} needs a write barrier.