Remove more dead code now that legacy const is gone

Neither globals nor lookup slots can be hole-initialized anymore, thus
removing some dead code from the code generators and runtime-scopes.

Review-Url: https://codereview.chromium.org/2051073004
Cr-Commit-Position: refs/heads/master@{#36876}

src/compiler/ast-graph-builder.cc

@@ -1132,13 +1132,9 @@ void AstGraphBuilder::VisitVariableDeclaration(VariableDeclaration* decl) {
       }
       break;
     case VariableLocation::LOOKUP: {
+      DCHECK(!hole_init);
       Node* name = jsgraph()->Constant(variable->name());
-      // For variables we must not push an initial value (such as 'undefined')
-      // because we may have a (legal) redeclaration and we must not destroy
-      // the current value.
-      Node* value =
-          hole_init ? jsgraph()->TheHoleConstant()
-                    : jsgraph()->ZeroConstant();  // Indicates no initial value.
+      Node* value = jsgraph()->ZeroConstant();  // Indicates no initial value.
       Node* attr =
           jsgraph()->Constant(variable->DeclarationPropertyAttributes());
       const Operator* op =

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

@@ -803,15 +803,8 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ mov(r2, Operand(variable->name()));
       // Declaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
-      } else {
+      DCHECK(!hole_init);
       __ mov(r0, Operand(Smi::FromInt(0)));  // Indicates no initial value.
-      }
       __ Push(r2, r0);
       __ Push(Smi::FromInt(variable->DeclarationPropertyAttributes()));
       __ CallRuntime(Runtime::kDeclareLookupSlot);

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

@@ -800,17 +800,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ Mov(x2, Operand(variable->name()));
       // Declaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ LoadRoot(x0, Heap::kTheHoleValueRootIndex);
-        __ Push(x2, x0);
-      } else {
+      DCHECK(!hole_init);
       // Pushing 0 (xzr) indicates no initial value.
       __ Push(x2, xzr);
-      }
       __ Push(Smi::FromInt(variable->DeclarationPropertyAttributes()));
       __ CallRuntime(Runtime::kDeclareLookupSlot);
       PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);

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

@@ -750,15 +750,8 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ push(Immediate(variable->name()));
       // VariableDeclaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ push(Immediate(isolate()->factory()->the_hole_value()));
-      } else {
+      DCHECK(!hole_init);
       __ push(Immediate(Smi::FromInt(0)));  // Indicates no initial value.
-      }
       __ push(
           Immediate(Smi::FromInt(variable->DeclarationPropertyAttributes())));
       __ CallRuntime(Runtime::kDeclareLookupSlot);

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

@@ -800,16 +800,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ li(a2, Operand(variable->name()));
       // Declaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ LoadRoot(a0, Heap::kTheHoleValueRootIndex);
-      } else {
+      DCHECK(!hole_init);
       DCHECK(Smi::FromInt(0) == 0);
       __ mov(a0, zero_reg);  // Smi::FromInt(0) indicates no initial value.
-      }
       __ Push(a2, a0);
       __ Push(Smi::FromInt(variable->DeclarationPropertyAttributes()));
       __ CallRuntime(Runtime::kDeclareLookupSlot);

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

@@ -799,16 +799,9 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ li(a2, Operand(variable->name()));
       // Declaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ LoadRoot(a0, Heap::kTheHoleValueRootIndex);
-      } else {
+      DCHECK(!hole_init);
       DCHECK(Smi::FromInt(0) == 0);
       __ mov(a0, zero_reg);  // Smi::FromInt(0) indicates no initial value.
-      }
       __ Push(a2, a0);
       __ Push(Smi::FromInt(variable->DeclarationPropertyAttributes()));
       __ CallRuntime(Runtime::kDeclareLookupSlot);

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

@@ -762,15 +762,8 @@ void FullCodeGenerator::VisitVariableDeclaration(
       __ Push(variable->name());
       // Declaration nodes are always introduced in one of four modes.
       DCHECK(IsDeclaredVariableMode(mode));
-      // Push initial value, if any.
-      // Note: For variables we must not push an initial value (such as
-      // 'undefined') because we may have a (legal) redeclaration and we
-      // must not destroy the current value.
-      if (hole_init) {
-        __ PushRoot(Heap::kTheHoleValueRootIndex);
-      } else {
+      DCHECK(!hole_init);
       __ Push(Smi::FromInt(0));  // Indicates no initial value.
-      }
       __ Push(Smi::FromInt(variable->DeclarationPropertyAttributes()));
       __ CallRuntime(Runtime::kDeclareLookupSlot);
       PrepareForBailoutForId(proxy->id(), BailoutState::NO_REGISTERS);

src/interpreter/bytecode-generator.cc

@@ -759,6 +759,7 @@ void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
       break;
     case VariableLocation::LOOKUP: {
       DCHECK(IsDeclaredVariableMode(mode));
+      DCHECK(!hole_init);
 
       register_allocator()->PrepareForConsecutiveAllocations(3);
       Register name = register_allocator()->NextConsecutiveRegister();
@@ -766,16 +767,9 @@ void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
       Register attributes = register_allocator()->NextConsecutiveRegister();
 
       builder()->LoadLiteral(variable->name()).StoreAccumulatorInRegister(name);
-      if (hole_init) {
-        builder()->LoadTheHole().StoreAccumulatorInRegister(init_value);
-      } else {
-        // For variables, we must not use an initial value (such as 'undefined')
-        // because we may have a (legal) redeclaration and we must not destroy
-        // the current value.
       builder()
           ->LoadLiteral(Smi::FromInt(0))
           .StoreAccumulatorInRegister(init_value);
-      }
       builder()
           ->LoadLiteral(Smi::FromInt(variable->DeclarationPropertyAttributes()))
           .StoreAccumulatorInRegister(attributes)

src/runtime/runtime-scopes.cc

@@ -34,7 +34,7 @@ RUNTIME_FUNCTION(Runtime_ThrowConstAssignError) {
 static Object* DeclareGlobals(Isolate* isolate, Handle<JSGlobalObject> global,
                               Handle<String> name, Handle<Object> value,
                               PropertyAttributes attr, bool is_var,
-                              bool is_const, bool is_function) {
+                              bool is_function) {
   Handle<ScriptContextTable> script_contexts(
       global->native_context()->script_context_table());
   ScriptContextTable::LookupResult lookup;
@@ -51,7 +51,6 @@ static Object* DeclareGlobals(Isolate* isolate, Handle<JSGlobalObject> global,
   if (it.IsFound()) {
     PropertyAttributes old_attributes = maybe.FromJust();
     // The name was declared before; check for conflicting re-declarations.
-    if (is_const) return ThrowRedeclarationError(isolate, name);
 
     // Skip var re-declarations.
     if (is_var) return isolate->heap()->undefined_value();
@@ -106,14 +105,9 @@ RUNTIME_FUNCTION(Runtime_DeclareGlobals) {
     Handle<String> name(String::cast(pairs->get(i)));
     Handle<Object> initial_value(pairs->get(i + 1), isolate);
 
-    // We have to declare a global const property. To capture we only
-    // assign to it when evaluating the assignment for "const x =
-    // <expr>" the initial value is the hole.
     bool is_var = initial_value->IsUndefined(isolate);
-    bool is_const = initial_value->IsTheHole(isolate);
     bool is_function = initial_value->IsSharedFunctionInfo();
-    DCHECK_EQ(1,
-              BoolToInt(is_var) + BoolToInt(is_const) + BoolToInt(is_function));
+    DCHECK_EQ(1, BoolToInt(is_var) + BoolToInt(is_function));
 
     Handle<Object> value;
     if (is_function) {
@@ -133,13 +127,12 @@ RUNTIME_FUNCTION(Runtime_DeclareGlobals) {
     bool is_native = DeclareGlobalsNativeFlag::decode(flags);
     bool is_eval = DeclareGlobalsEvalFlag::decode(flags);
     int attr = NONE;
-    if (is_const) attr |= READ_ONLY;
     if (is_function && is_native) attr |= READ_ONLY;
-    if (!is_const && !is_eval) attr |= DONT_DELETE;
+    if (!is_eval) attr |= DONT_DELETE;
 
     Object* result = DeclareGlobals(isolate, global, name, value,
                                     static_cast<PropertyAttributes>(attr),
-                                    is_var, is_const, is_function);
+                                    is_var, is_function);
     if (isolate->has_pending_exception()) return result;
   });
 
@@ -210,10 +203,8 @@ Object* DeclareLookupSlot(Isolate* isolate, Handle<String> name,
 
   // TODO(verwaest): Unify the encoding indicating "var" with DeclareGlobals.
   bool is_var = *initial_value == NULL;
-  bool is_const = initial_value->IsTheHole(isolate);
   bool is_function = initial_value->IsJSFunction();
-  DCHECK_EQ(1,
-            BoolToInt(is_var) + BoolToInt(is_const) + BoolToInt(is_function));
+  DCHECK_EQ(1, BoolToInt(is_var) + BoolToInt(is_function));
 
   int index;
   PropertyAttributes attributes;
@@ -245,24 +236,24 @@ Object* DeclareLookupSlot(Isolate* isolate, Handle<String> name,
   // but by DeclareGlobals instead.
   if (attributes != ABSENT && holder->IsJSGlobalObject()) {
     return DeclareGlobals(isolate, Handle<JSGlobalObject>::cast(holder), name,
-                          value, attr, is_var, is_const, is_function);
+                          value, attr, is_var, is_function);
   }
   if (context_arg->extension()->IsJSGlobalObject()) {
     Handle<JSGlobalObject> global(
         JSGlobalObject::cast(context_arg->extension()), isolate);
-    return DeclareGlobals(isolate, global, name, value, attr, is_var, is_const,
+    return DeclareGlobals(isolate, global, name, value, attr, is_var,
                           is_function);
   } else if (context->IsScriptContext()) {
     DCHECK(context->global_object()->IsJSGlobalObject());
     Handle<JSGlobalObject> global(
         JSGlobalObject::cast(context->global_object()), isolate);
-    return DeclareGlobals(isolate, global, name, value, attr, is_var, is_const,
+    return DeclareGlobals(isolate, global, name, value, attr, is_var,
                           is_function);
   }
 
   if (attributes != ABSENT) {
     // The name was declared before; check for conflicting re-declarations.
-    if (is_const || (attributes & READ_ONLY) != 0) {
+    if ((attributes & READ_ONLY) != 0) {
       return ThrowRedeclarationError(isolate, name);
     }