[full-codegen] Eliminate unnecessary hole checks for stores

Loads already used source position elimination to avoid unnecessary hole checks,
but for reasons unknown stores did not. This CL corrects that, making full-codegen's
hole elimination equivalent to ignition's.

Also introduced a HoleCheckMode enum class to avoid more bool flags and updated
VariableProxy and BytecodeGenerator appropriately.

Review-Url: https://codereview.chromium.org/2441543005
Cr-Commit-Position: refs/heads/master@{#40522}

src/ast/ast.cc

@@ -165,9 +165,10 @@ VariableProxy::VariableProxy(Variable* var, int start_position,
       end_position_(end_position),
       raw_name_(var->raw_name()),
       next_unresolved_(nullptr) {
-  bit_field_ |=
-      IsThisField::encode(var->is_this()) | IsAssignedField::encode(false) |
-      IsResolvedField::encode(false) | NeedsHoleCheckField::encode(false);
+  bit_field_ |= IsThisField::encode(var->is_this()) |
+                IsAssignedField::encode(false) |
+                IsResolvedField::encode(false) |
+                HoleCheckModeField::encode(HoleCheckMode::kElided);
   BindTo(var);
 }
 
@@ -181,7 +182,7 @@ VariableProxy::VariableProxy(const AstRawString* name,
   bit_field_ |= IsThisField::encode(variable_kind == THIS_VARIABLE) |
                 IsAssignedField::encode(false) |
                 IsResolvedField::encode(false) |
-                NeedsHoleCheckField::encode(false);
+                HoleCheckModeField::encode(HoleCheckMode::kElided);
 }
 
 VariableProxy::VariableProxy(const VariableProxy* copy_from)

src/ast/ast.h

@@ -1671,11 +1671,12 @@ class VariableProxy final : public Expression {
     bit_field_ = IsNewTargetField::update(bit_field_, true);
   }
 
-  bool needs_hole_check() const {
-    return NeedsHoleCheckField::decode(bit_field_);
+  HoleCheckMode hole_check_mode() const {
+    return HoleCheckModeField::decode(bit_field_);
   }
   void set_needs_hole_check() {
-    bit_field_ = NeedsHoleCheckField::update(bit_field_, true);
+    bit_field_ =
+        HoleCheckModeField::update(bit_field_, HoleCheckMode::kRequired);
   }
 
   int end_position() const { return end_position_; }
@@ -1713,8 +1714,8 @@ class VariableProxy final : public Expression {
   class IsAssignedField : public BitField<bool, IsThisField::kNext, 1> {};
   class IsResolvedField : public BitField<bool, IsAssignedField::kNext, 1> {};
   class IsNewTargetField : public BitField<bool, IsResolvedField::kNext, 1> {};
-  class NeedsHoleCheckField
-      : public BitField<bool, IsNewTargetField::kNext, 1> {};
+  class HoleCheckModeField
+      : public BitField<HoleCheckMode, IsNewTargetField::kNext, 1> {};
 
   // Position is stored in the AstNode superclass, but VariableProxy needs to
   // know its end position too (for error messages). It cannot be inferred from

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

@@ -1287,7 +1287,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->needs_hole_check()) {
+      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
         // Throw a reference error when using an uninitialized let/const
         // binding in harmony mode.
         Label done;
@@ -1730,12 +1730,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(r0);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -2017,9 +2019,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -2094,9 +2097,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
@@ -2107,7 +2110,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     MemOperand location = VarOperand(var, r1);
     // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
+    if (hole_check_mode == HoleCheckMode::kRequired) {
       Label assign;
       __ ldr(r3, location);
       __ CompareRoot(r3, Heap::kTheHoleValueRootIndex);
@@ -3188,11 +3191,12 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in r0.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(r0);
@@ -3203,13 +3207,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(r0);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       PopOperand(StoreDescriptor::ReceiverRegister());
       CallStoreIC(expr->CountSlot(), prop->key()->AsLiteral()->value());

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

@@ -1275,7 +1275,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       Comment cmnt(masm_, var->IsContextSlot()
                               ? "Context variable"
                               : "Stack variable");
-      if (proxy->needs_hole_check()) {
+      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
         // Throw a reference error when using an uninitialized let/const
         // binding in harmony mode.
         Label done;
@@ -1710,12 +1710,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(x0);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -1908,9 +1910,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -1987,9 +1990,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   ASM_LOCATION("FullCodeGenerator::EmitVariableAssignment");
   if (var->IsUnallocated()) {
     // Global var, const, or let.
@@ -3106,11 +3109,12 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in x0.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(x0);
@@ -3121,13 +3125,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(x0);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       PopOperand(StoreDescriptor::ReceiverRegister());
       CallStoreIC(expr->CountSlot(), prop->key()->AsLiteral()->value());

src/full-codegen/full-codegen.cc

@@ -1582,7 +1582,7 @@ void FullCodeGenerator::VisitClassLiteral(ClassLiteral* lit) {
 
   if (lit->class_variable_proxy() != nullptr) {
     EmitVariableAssignment(lit->class_variable_proxy()->var(), Token::INIT,
-                           lit->ProxySlot());
+                           lit->ProxySlot(), HoleCheckMode::kElided);
   }
 
   context()->Plug(result_register());

src/full-codegen/full-codegen.h

@@ -572,7 +572,8 @@ 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);
+                              FeedbackVectorSlot slot,
+                              HoleCheckMode hole_check_mode);
 
   // Helper functions to EmitVariableAssignment
   void EmitStoreToStackLocalOrContextSlot(Variable* var,

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

@@ -1210,7 +1210,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
 
-      if (proxy->needs_hole_check()) {
+      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
         // Throw a reference error when using an uninitialized let/const
         // binding in harmony mode.
         Label done;
@@ -1643,12 +1643,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(eax);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -1927,9 +1929,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -2002,9 +2005,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ReceiverRegister(), NativeContextOperand());
@@ -2018,7 +2021,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     MemOperand location = VarOperand(var, ecx);
     // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
+    if (hole_check_mode == HoleCheckMode::kRequired) {
       Label assign;
       __ mov(edx, location);
       __ cmp(edx, isolate()->factory()->the_hole_value());
@@ -3084,12 +3087,13 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in eax.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         // Perform the assignment as if via '='.
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(eax);
@@ -3101,13 +3105,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
         }
       } else {
         // Perform the assignment as if via '='.
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(eax);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       PopOperand(StoreDescriptor::ReceiverRegister());
       CallStoreIC(expr->CountSlot(), prop->key()->AsLiteral()->value());

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

@@ -1287,7 +1287,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->needs_hole_check()) {
+      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
         // Throw a reference error when using an uninitialized let/const
         // binding in harmony mode.
         Label done;
@@ -1731,12 +1731,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(v0);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -2025,9 +2027,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -2102,9 +2105,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ValueRegister(), result_register());
@@ -2116,7 +2119,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     MemOperand location = VarOperand(var, a1);
     // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
+    if (hole_check_mode == HoleCheckMode::kRequired) {
       Label assign;
       __ lw(a3, location);
       __ LoadRoot(t0, Heap::kTheHoleValueRootIndex);
@@ -3195,11 +3198,12 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in v0.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(v0);
@@ -3210,13 +3214,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(v0);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       __ mov(StoreDescriptor::ValueRegister(), result_register());
       PopOperand(StoreDescriptor::ReceiverRegister());

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

@@ -1288,7 +1288,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (proxy->needs_hole_check()) {
+      if (proxy->hole_check_mode() == HoleCheckMode::kRequired) {
         // Throw a reference error when using an uninitialized let/const
         // binding in harmony mode.
         Label done;
@@ -1732,12 +1732,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(v0);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -2025,9 +2027,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -2102,9 +2105,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ mov(StoreDescriptor::ValueRegister(), result_register());
@@ -2116,7 +2119,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     MemOperand location = VarOperand(var, a1);
     // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
+    if (hole_check_mode == HoleCheckMode::kRequired) {
       Label assign;
       __ ld(a3, location);
       __ LoadRoot(a4, Heap::kTheHoleValueRootIndex);
@@ -3195,11 +3198,12 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in v0.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(v0);
@@ -3210,13 +3214,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
           context()->PlugTOS();
         }
       } else {
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(v0);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       __ mov(StoreDescriptor::ValueRegister(), result_register());
       PopOperand(StoreDescriptor::ReceiverRegister());

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

@@ -1239,7 +1239,7 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy,
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context slot"
                                                : "[ Stack slot");
-      if (proxy->needs_hole_check()) {
+      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()));
@@ -1670,12 +1670,14 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 
   // Store the value.
   switch (assign_type) {
-    case VARIABLE:
-      EmitVariableAssignment(expr->target()->AsVariableProxy()->var(),
-                             expr->op(), expr->AssignmentSlot());
+    case VARIABLE: {
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      EmitVariableAssignment(proxy->var(), expr->op(), expr->AssignmentSlot(),
+                             proxy->hole_check_mode());
       PrepareForBailoutForId(expr->AssignmentId(), BailoutState::TOS_REGISTER);
       context()->Plug(rax);
       break;
+    }
     case NAMED_PROPERTY:
       EmitNamedPropertyAssignment(expr);
       break;
@@ -1919,9 +1921,10 @@ void FullCodeGenerator::EmitAssignment(Expression* expr,
 
   switch (assign_type) {
     case VARIABLE: {
-      Variable* var = expr->AsVariableProxy()->var();
+      VariableProxy* proxy = expr->AsVariableProxy();
       EffectContext context(this);
-      EmitVariableAssignment(var, Token::ASSIGN, slot);
+      EmitVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                             proxy->hole_check_mode());
       break;
     }
     case NAMED_PROPERTY: {
@@ -1994,9 +1997,9 @@ void FullCodeGenerator::EmitStoreToStackLocalOrContextSlot(
   }
 }
 
-
 void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
-                                               FeedbackVectorSlot slot) {
+                                               FeedbackVectorSlot slot,
+                                               HoleCheckMode hole_check_mode) {
   if (var->IsUnallocated()) {
     // Global var, const, or let.
     __ LoadGlobalObject(StoreDescriptor::ReceiverRegister());
@@ -2007,7 +2010,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     DCHECK(var->IsStackAllocated() || var->IsContextSlot());
     MemOperand location = VarOperand(var, rcx);
     // Perform an initialization check for lexically declared variables.
-    if (var->binding_needs_init()) {
+    if (hole_check_mode == HoleCheckMode::kRequired) {
       Label assign;
       __ movp(rdx, location);
       __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
@@ -3073,12 +3076,13 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
 
   // Store the value returned in rax.
   switch (assign_type) {
-    case VARIABLE:
+    case VARIABLE: {
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
       if (expr->is_postfix()) {
         // Perform the assignment as if via '='.
         { EffectContext context(this);
-          EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                                 Token::ASSIGN, expr->CountSlot());
+          EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                                 proxy->hole_check_mode());
           PrepareForBailoutForId(expr->AssignmentId(),
                                  BailoutState::TOS_REGISTER);
           context.Plug(rax);
@@ -3090,13 +3094,14 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
         }
       } else {
         // Perform the assignment as if via '='.
-        EmitVariableAssignment(expr->expression()->AsVariableProxy()->var(),
-                               Token::ASSIGN, expr->CountSlot());
+        EmitVariableAssignment(proxy->var(), Token::ASSIGN, expr->CountSlot(),
+                               proxy->hole_check_mode());
         PrepareForBailoutForId(expr->AssignmentId(),
                                BailoutState::TOS_REGISTER);
         context()->Plug(rax);
       }
       break;
+    }
     case NAMED_PROPERTY: {
       PopOperand(StoreDescriptor::ReceiverRegister());
       CallStoreIC(expr->CountSlot(), prop->key()->AsLiteral()->value());

src/globals.h

@@ -1049,6 +1049,8 @@ enum VariableLocation : uint8_t {
 // immediately initialized upon creation (kCreatedInitialized).
 enum InitializationFlag : uint8_t { kNeedsInitialization, kCreatedInitialized };
 
+enum class HoleCheckMode { kRequired, kElided };
+
 enum MaybeAssignedFlag : uint8_t { kNotAssigned, kMaybeAssigned };
 
 // Serialized in PreparseData, so numeric values should not be changed.

src/interpreter/bytecode-generator.h

@@ -95,13 +95,15 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
   void VisitPropertyLoadForAccumulator(Register obj, Property* expr);
 
   void BuildVariableLoad(Variable* variable, FeedbackVectorSlot slot,
-                         bool needs_hole_check,
+                         HoleCheckMode hole_check_mode,
                          TypeofMode typeof_mode = NOT_INSIDE_TYPEOF);
   void BuildVariableLoadForAccumulatorValue(
-      Variable* variable, FeedbackVectorSlot slot, bool needs_hole_check,
+      Variable* variable, FeedbackVectorSlot slot,
+      HoleCheckMode hole_check_mode,
       TypeofMode typeof_mode = NOT_INSIDE_TYPEOF);
   void BuildVariableAssignment(Variable* variable, Token::Value op,
-                               FeedbackVectorSlot slot, bool needs_hole_check);
+                               FeedbackVectorSlot slot,
+                               HoleCheckMode hole_check_mode);
 
   void BuildReturn();
   void BuildReThrow();