[fullcodegen] Remove dead hole check logic

Variables requiring initialization are already forced into ignition,
so all the code supporting hole checks in full-codegen and
ast-graph-builder is dead.

R=bmeurer@chromium.org
BUG=v8:5657

Review-Url: https://codereview.chromium.org/2615033002
Cr-Commit-Position: refs/heads/master@{#42112}

src/compiler/ast-graph-builder.h

@@ -309,15 +309,8 @@ class AstGraphBuilder : public AstVisitor<AstGraphBuilder> {
 
   // Builders for error reporting at runtime.
   Node* BuildThrowError(Node* exception, BailoutId bailout_id);
-  Node* BuildThrowReferenceError(Variable* var, BailoutId bailout_id);
   Node* BuildThrowConstAssignError(BailoutId bailout_id);
 
-  // Builders for dynamic hole-checks at runtime.
-  Node* BuildHoleCheckThenThrow(Node* value, Variable* var, Node* not_hole,
-                                BailoutId bailout_id);
-  Node* BuildHoleCheckElseThrow(Node* value, Variable* var, Node* for_hole,
-                                BailoutId bailout_id);
-
   // Builders for non-local control flow.
   Node* BuildReturn(Node* return_value);
   Node* BuildThrow(Node* exception_value);

src/full-codegen/arm/full-codegen-arm.cc

@@ -755,9 +755,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -767,22 +767,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
-        __ str(r0, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
-        __ str(r0, ContextMemOperand(cp, variable->index()));
-        // No write barrier since the_hole_value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1147,6 +1132,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1163,20 +1149,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(r0, var);
-        __ CompareRoot(r0, Heap::kTheHoleValueRootIndex);
-        __ b(ne, &done);
-        __ mov(r0, Operand(var->name()));
-        __ push(r0);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(r0);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1493,8 +1465,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(r0);
       break;
@@ -1676,8 +1647,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1720,60 +1690,22 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, r1);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ ldr(r3, location);
-      __ CompareRoot(r3, Heap::kTheHoleValueRootIndex);
-      __ b(ne, &assign);
-      __ mov(r3, Operand(var->name()));
-      __ push(r3);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, r1);
-    __ ldr(r3, location);
-    __ CompareRoot(r3, Heap::kTheHoleValueRootIndex);
-    __ b(eq, &uninitialized_this);
-    __ mov(r0, Operand(var->name()));
-    __ Push(r0);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, r1);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ ldr(r2, location);
-      __ CompareRoot(r2, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2505,8 +2437,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(r0);
@@ -2517,8 +2449,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(r0);

src/full-codegen/arm64/full-codegen-arm64.cc

@@ -750,9 +750,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -762,22 +762,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(x10, Heap::kTheHoleValueRootIndex);
-        __ Str(x10, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ LoadRoot(x10, Heap::kTheHoleValueRootIndex);
-        __ Str(x10, ContextMemOperand(cp, variable->index()));
-        // No write barrier since the_hole_value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1134,6 +1119,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1151,19 +1137,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       Comment cmnt(masm_, var->IsContextSlot()
                               ? "Context variable"
                               : "Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(x0, var);
-        __ JumpIfNotRoot(x0, Heap::kTheHoleValueRootIndex, &done);
-        __ Mov(x0, Operand(var->name()));
-        __ Push(x0);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ Bind(&done);
-        context()->Plug(x0);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1477,8 +1450,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(x0);
       break;
@@ -1619,8 +1591,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1665,58 +1636,23 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
   ASM_LOCATION("FullCodeGenerator::EmitVariableAssignment");
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, x1);
-    // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
-      Label assign;
-      __ Ldr(x10, location);
-      __ JumpIfNotRoot(x10, Heap::kTheHoleValueRootIndex, &assign);
-      __ Mov(x10, Operand(var->name()));
-      __ Push(x10);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ Bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, x1);
-    __ Ldr(x10, location);
-    __ JumpIfRoot(x10, Heap::kTheHoleValueRootIndex, &uninitialized_this);
-    __ Mov(x0, Operand(var->name()));
-    __ Push(x0);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, x1);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      __ Ldr(x10, location);
-      __ CompareRoot(x10, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2471,8 +2407,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(x0);
@@ -2483,8 +2419,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(x0);

src/full-codegen/full-codegen.h

@@ -475,8 +475,7 @@ class FullCodeGenerator final : public AstVisitor<FullCodeGenerator> {
   // Complete a variable assignment.  The right-hand-side value is expected
   // in the accumulator.
   void EmitVariableAssignment(Variable* var, Token::Value op,
-                              FeedbackVectorSlot slot,
-                              HoleCheckMode hole_check_mode);
+                              FeedbackVectorSlot slot);
 
   // Helper functions to EmitVariableAssignment
   void EmitStoreToStackLocalOrContextSlot(Variable* var,

src/full-codegen/ia32/full-codegen-ia32.cc

@@ -703,9 +703,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -715,22 +715,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ mov(StackOperand(variable),
-               Immediate(isolate()->factory()->the_hole_value()));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ mov(ContextOperand(esi, variable->index()),
-               Immediate(isolate()->factory()->the_hole_value()));
-        // No write barrier since the hole value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1074,6 +1059,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1090,20 +1076,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(eax, var);
-        __ cmp(eax, isolate()->factory()->the_hole_value());
-        __ j(not_equal, &done, Label::kNear);
-        __ push(Immediate(var->name()));
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(eax);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1419,8 +1391,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(eax);
       break;
@@ -1601,8 +1572,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1643,8 +1613,8 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ReceiverRegister(), NativeContextOperand());
@@ -1653,51 +1623,15 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
                           Context::EXTENSION_INDEX));
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, ecx);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ mov(edx, location);
-      __ cmp(edx, isolate()->factory()->the_hole_value());
-      __ j(not_equal, &assign, Label::kNear);
-      __ push(Immediate(var->name()));
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, ecx);
-    __ mov(edx, location);
-    __ cmp(edx, isolate()->factory()->the_hole_value());
-    __ j(equal, &uninitialized_this);
-    __ push(Immediate(var->name()));
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, ecx);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ mov(edx, location);
-      __ cmp(edx, isolate()->factory()->the_hole_value());
-      __ Check(equal, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2439,8 +2373,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       if (expr->is_postfix()) {
         // Perform the assignment as if via '='.
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(eax);
@@ -2452,8 +2386,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
         }
       } else {
         // Perform the assignment as if via '='.
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(eax);

src/full-codegen/mips/full-codegen-mips.cc

@@ -754,9 +754,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -766,22 +766,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(t0, Heap::kTheHoleValueRootIndex);
-        __ sw(t0, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-          __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-          __ sw(at, ContextMemOperand(cp, variable->index()));
-          // No write barrier since the_hole_value is in old space.
-          PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1146,6 +1131,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1162,21 +1148,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(v0, var);
-        __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-        __ subu(at, v0, at);  // Sub as compare: at == 0 on eq.
-        __ Branch(&done, ne, at, Operand(zero_reg));
-        __ li(a0, Operand(var->name()));
-        __ push(a0);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(v0);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1496,8 +1467,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(v0);
       break;
@@ -1689,8 +1659,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1733,61 +1702,23 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ValueRegister(), result_register());
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, a1);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ lw(a3, location);
-      __ LoadRoot(t0, Heap::kTheHoleValueRootIndex);
-      __ Branch(&assign, ne, a3, Operand(t0));
-      __ li(a3, Operand(var->name()));
-      __ push(a3);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, a1);
-    __ lw(a3, location);
-    __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-    __ Branch(&uninitialized_this, eq, a3, Operand(at));
-    __ li(a0, Operand(var->name()));
-    __ Push(a0);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK((var->IsStackAllocated() || var->IsContextSlot()));
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, a1);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ lw(a2, location);
-      __ LoadRoot(t0, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization, a2, Operand(t0));
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2529,8 +2460,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(v0);
@@ -2541,8 +2472,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(v0);

src/full-codegen/mips64/full-codegen-mips64.cc

@@ -754,9 +754,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -766,22 +766,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(a4, Heap::kTheHoleValueRootIndex);
-        __ sd(a4, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-          __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-          __ sd(at, ContextMemOperand(cp, variable->index()));
-          // No write barrier since the_hole_value is in old space.
-          PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1148,6 +1133,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1164,21 +1150,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(v0, var);
-        __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-        __ dsubu(at, v0, at);  // Sub as compare: at == 0 on eq.
-        __ Branch(&done, ne, at, Operand(zero_reg));
-        __ li(a0, Operand(var->name()));
-        __ push(a0);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(v0);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1498,8 +1469,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(v0);
       break;
@@ -1690,8 +1660,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1734,61 +1703,23 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ValueRegister(), result_register());
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, a1);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ ld(a3, location);
-      __ LoadRoot(a4, Heap::kTheHoleValueRootIndex);
-      __ Branch(&assign, ne, a3, Operand(a4));
-      __ li(a3, Operand(var->name()));
-      __ push(a3);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, a1);
-    __ ld(a3, location);
-    __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-    __ Branch(&uninitialized_this, eq, a3, Operand(at));
-    __ li(a0, Operand(var->name()));
-    __ Push(a0);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK((var->IsStackAllocated() || var->IsContextSlot()));
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, a1);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ ld(a2, location);
-      __ LoadRoot(a4, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization, a2, Operand(a4));
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2530,8 +2461,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(v0);
@@ -2542,8 +2473,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(v0);

src/full-codegen/ppc/full-codegen-ppc.cc

@@ -723,9 +723,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -735,22 +735,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-        __ StoreP(ip, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-        __ StoreP(ip, ContextMemOperand(cp, variable->index()), r0);
-        // No write barrier since the_hole_value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1118,6 +1103,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1134,20 +1120,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(r3, var);
-        __ CompareRoot(r3, Heap::kTheHoleValueRootIndex);
-        __ bne(&done);
-        __ mov(r3, Operand(var->name()));
-        __ push(r3);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(r3);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1461,8 +1433,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(r3);
       break;
@@ -1689,8 +1660,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1733,60 +1703,22 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, r4);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ LoadP(r6, location);
-      __ CompareRoot(r6, Heap::kTheHoleValueRootIndex);
-      __ bne(&assign);
-      __ mov(r6, Operand(var->name()));
-      __ push(r6);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, r4);
-    __ LoadP(r6, location);
-    __ CompareRoot(r6, Heap::kTheHoleValueRootIndex);
-    __ beq(&uninitialized_this);
-    __ mov(r4, Operand(var->name()));
-    __ push(r4);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK((var->IsStackAllocated() || var->IsContextSlot()));
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, r4);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ LoadP(r5, location);
-      __ CompareRoot(r5, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2517,8 +2449,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       if (expr->is_postfix()) {
         {
           EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(r3);
@@ -2529,8 +2461,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(r3);

src/full-codegen/s390/full-codegen-s390.cc

@@ -696,9 +696,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -708,22 +708,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-        __ StoreP(ip, StackOperand(variable));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-        __ StoreP(ip, ContextMemOperand(cp, variable->index()));
-        // No write barrier since the_hole_value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1099,20 +1084,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(r2, var);
-        __ CompareRoot(r2, Heap::kTheHoleValueRootIndex);
-        __ bne(&done);
-        __ mov(r2, Operand(var->name()));
-        __ push(r2);
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(r2);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1422,8 +1393,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(r2);
       break;
@@ -1649,8 +1619,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1692,60 +1661,22 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    // Non-initializing assignment to let variable needs a write barrier.
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, r3);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ LoadP(r5, location);
-      __ CompareRoot(r5, Heap::kTheHoleValueRootIndex);
-      __ bne(&assign);
-      __ mov(r5, Operand(var->name()));
-      __ push(r5);
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, r3);
-    __ LoadP(r5, location);
-    __ CompareRoot(r5, Heap::kTheHoleValueRootIndex);
-    __ beq(&uninitialized_this);
-    __ mov(r3, Operand(var->name()));
-    __ push(r3);
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK((var->IsStackAllocated() || var->IsContextSlot()));
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, r3);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ LoadP(r4, location);
-      __ CompareRoot(r4, Heap::kTheHoleValueRootIndex);
-      __ Check(eq, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2458,8 +2389,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       if (expr->is_postfix()) {
         {
           EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(r2);
@@ -2470,8 +2401,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(r2);

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

@@ -717,9 +717,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -729,22 +729,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
-        __ movp(StackOperand(variable), kScratchRegister);
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
-        __ movp(ContextOperand(rsi, variable->index()), kScratchRegister);
-        // No write barrier since the hole value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1104,6 +1089,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variable, and all other types of variables.
   switch (var->location()) {
@@ -1120,20 +1106,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context slot"
                                                : "[ Stack slot");
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // 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);
-        __ Push(var->name());
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(rax);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1446,8 +1418,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(rax);
       break;
@@ -1593,8 +1564,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1635,59 +1605,22 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, rcx);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      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) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, rcx);
-    __ movp(rdx, location);
-    __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
-    __ j(equal, &uninitialized_this);
-    __ Push(var->name());
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, rcx);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ movp(rdx, location);
-      __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
-      __ Check(equal, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2424,8 +2357,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       if (expr->is_postfix()) {
         // Perform the assignment as if via '='.
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(rax);
@@ -2437,8 +2370,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
         }
       } else {
         // Perform the assignment as if via '='.
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(rax);

src/full-codegen/x87/full-codegen-x87.cc

@@ -700,9 +700,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
     VariableDeclaration* declaration) {
   VariableProxy* proxy = declaration->proxy();
   Variable* variable = proxy->var();
+  DCHECK(!variable->binding_needs_init());
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
-      DCHECK(!variable->binding_needs_init());
       globals_->Add(variable->name(), zone());
       FeedbackVectorSlot slot = proxy->VariableFeedbackSlot();
       DCHECK(!slot.IsInvalid());
@@ -712,22 +712,7 @@ void FullCodeGenerator::VisitVariableDeclaration(
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        __ mov(StackOperand(variable),
-               Immediate(isolate()->factory()->the_hole_value()));
-      }
-      break;
-
     case VariableLocation::CONTEXT:
-      if (variable->binding_needs_init()) {
-        Comment cmnt(masm_, "[ VariableDeclaration");
-        EmitDebugCheckDeclarationContext(variable);
-        __ mov(ContextOperand(esi, variable->index()),
-               Immediate(isolate()->factory()->the_hole_value()));
-        // No write barrier since the hole value is in old space.
-        PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);
-      }
       break;
 
     case VariableLocation::LOOKUP:
@@ -1066,6 +1051,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
   SetExpressionPosition(proxy);
   PrepareForBailoutForId(proxy->BeforeId(), BailoutState::NO_REGISTERS);
   Variable* var = proxy->var();
+  DCHECK(!var->binding_needs_init());
 
   // Two cases: global variables and all other types of variables.
   switch (var->location()) {
@@ -1082,20 +1068,6 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-
-      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
-        // Throw a reference error when using an uninitialized let/const
-        // binding in harmony mode.
-        Label done;
-        GetVar(eax, var);
-        __ cmp(eax, isolate()->factory()->the_hole_value());
-        __ j(not_equal, &done, Label::kNear);
-        __ push(Immediate(var->name()));
-        __ CallRuntime(Runtime::kThrowReferenceError);
-        __ bind(&done);
-        context()->Plug(eax);
-        break;
-      }
       context()->Plug(var);
       break;
     }
@@ -1411,8 +1383,7 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->target()->AsVariableProxy();
-      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(eax);
       break;
@@ -1593,8 +1564,7 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
     case VARIABLE: {
       VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
-                             proxy->hole_check_mode());
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot);
       break;
     }
     case NAMED_PROPERTY: {
@@ -1635,8 +1605,8 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
 }
 
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot,
-                                               HoleCheckMode hole_check_mode) {
+                                               FeedbackVectorSlot slot) {
+  DCHECK(!var->binding_needs_init());
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ReceiverRegister(), NativeContextOperand());
@@ -1645,51 +1615,15 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
                           Context::EXTENSION_INDEX));
     CallStoreIC(slot, var->name());
 
-  } else if (IsLexicalVariableMode(var->mode()) && op != Token::INIT) {
-    DCHECK(!var->IsLookupSlot());
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    MemOperand location = VarOperand(var, ecx);
-    // Perform an initialization check for lexically declared variables.
-    if (hole_check_mode == HoleCheckMode::kRequired) {
-      Label assign;
-      __ mov(edx, location);
-      __ cmp(edx, isolate()->factory()->the_hole_value());
-      __ j(not_equal, &assign, Label::kNear);
-      __ push(Immediate(var->name()));
-      __ CallRuntime(Runtime::kThrowReferenceError);
-      __ bind(&assign);
-    }
-    if (var->mode() != CONST) {
-      EmitStoreToStackLocalOrContextSlot(var, location);
-    } else if (var->throw_on_const_assignment(language_mode())) {
+  } else if (var->mode() == CONST && op != Token::INIT) {
+    if (var->throw_on_const_assignment(language_mode())) {
       __ CallRuntime(Runtime::kThrowConstAssignError);
     }
-  } else if (var->is_this() && var->mode() == CONST && op == Token::INIT) {
-    // Initializing assignment to const {this} needs a write barrier.
-    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
-    Label uninitialized_this;
-    MemOperand location = VarOperand(var, ecx);
-    __ mov(edx, location);
-    __ cmp(edx, isolate()->factory()->the_hole_value());
-    __ j(equal, &uninitialized_this);
-    __ push(Immediate(var->name()));
-    __ CallRuntime(Runtime::kThrowReferenceError);
-    __ bind(&uninitialized_this);
-    EmitStoreToStackLocalOrContextSlot(var, location);
-
   } else {
-    DCHECK(var->mode() != CONST || op == Token::INIT);
+    DCHECK(!var->is_this());
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     DCHECK(!var->IsLookupSlot());
-    // Assignment to var or initializing assignment to let/const in harmony
-    // mode.
     MemOperand location = VarOperand(var, ecx);
-    if (FLAG_debug_code && var->mode() == LET && op == Token::INIT) {
-      // Check for an uninitialized let binding.
-      __ mov(edx, location);
-      __ cmp(edx, isolate()->factory()->the_hole_value());
-      __ Check(equal, kLetBindingReInitialization);
-    }
     EmitStoreToStackLocalOrContextSlot(var, location);
   }
 }
@@ -2431,8 +2365,8 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
       if (expr->is_postfix()) {
         // Perform the assignment as if via '='.
         { EffectContext context(this);
-          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                                 proxy->hole_check_mode());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN,
+                                 expr->CountSlot());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(eax);
@@ -2444,8 +2378,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
         }
       } else {
         // Perform the assignment as if via '='.
-        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
-                               proxy->hole_check_mode());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(eax);