Use Variable::binding_needs_init() to determine hole initialization

src/interpreter/bytecode-generator.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-flags.h"
@@ skipping 814 matching lines @@
   ControlScopeForBreakable execution_control(this, stmt, &block_builder);
   if (stmt->scope() != nullptr) {
     VisitDeclarations(stmt->scope()->declarations());
   }
   VisitStatements(stmt->statements());
   if (stmt->labels() != nullptr) block_builder.EndBlock();
 }
 
 void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
   Variable* variable = decl->proxy()->var();
-  VariableMode mode = decl->mode();
-  // Const and let variables are initialized with the hole so that we can
-  // check that they are only assigned once.
-  bool hole_init = mode == CONST || mode == LET;
   switch (variable->location()) {
     case VariableLocation::GLOBAL:
     case VariableLocation::UNALLOCATED: {
       DCHECK(!variable->binding_needs_init());
       FeedbackVectorSlot slot = decl->proxy()->VariableFeedbackSlot();
       globals_builder()->AddUndefinedDeclaration(slot);
       break;
     }
     case VariableLocation::LOCAL:
-      if (hole_init) {
+      if (variable->binding_needs_init()) {
         Register destination(variable->index());
         builder()->LoadTheHole().StoreAccumulatorInRegister(destination);
       }
       break;
     case VariableLocation::PARAMETER:
-      if (hole_init) {
+      if (variable->binding_needs_init()) {
         // The parameter indices are shifted by 1 (receiver is variable
         // index -1 but is parameter index 0 in BytecodeArrayBuilder).
         Register destination(builder()->Parameter(variable->index() + 1));
         builder()->LoadTheHole().StoreAccumulatorInRegister(destination);
       }
       break;
     case VariableLocation::CONTEXT:
-      if (hole_init) {
+      if (variable->binding_needs_init()) {
         builder()->LoadTheHole().StoreContextSlot(execution_context()->reg(),
                                                   variable->index());
       }
       break;
     case VariableLocation::LOOKUP: {
-      DCHECK_EQ(VAR, mode);
-      DCHECK(!hole_init);
+      DCHECK_EQ(VAR, variable->mode());
+      DCHECK(!variable->binding_needs_init());
 
       Register name = register_allocator()->NewRegister();
 
       builder()
           ->LoadLiteral(variable->name())
           .StoreAccumulatorInRegister(name)
           .CallRuntime(Runtime::kDeclareEvalVar, name, 1);
       break;
     }
   }
@@ skipping 956 matching lines @@
     builder()->LoadAccumulatorWithRegister(literal);
   }
   execution_result()->SetResultInAccumulator();
 }
 
 void BytecodeGenerator::VisitVariableProxy(VariableProxy* proxy) {
   builder()->SetExpressionPosition(proxy);
   VisitVariableLoad(proxy->var(), proxy->VariableFeedbackSlot());
 }
 
-void BytecodeGenerator::BuildHoleCheckForVariableLoad(VariableMode mode,
-                                                      Handle<String> name) {
-  if (mode == LET || mode == CONST) {
-    BuildThrowIfHole(name);
+void BytecodeGenerator::BuildHoleCheckForVariableLoad(Variable* variable) {
+  if (variable->binding_needs_init()) {
+    BuildThrowIfHole(variable->name());
   }
 }
 
 void BytecodeGenerator::VisitVariableLoad(Variable* variable,
                                           FeedbackVectorSlot slot,
                                           TypeofMode typeof_mode) {
-  VariableMode mode = variable->mode();
   switch (variable->location()) {
     case VariableLocation::LOCAL: {
       Register source(Register(variable->index()));
       builder()->LoadAccumulatorWithRegister(source);
-      BuildHoleCheckForVariableLoad(mode, variable->name());
+      BuildHoleCheckForVariableLoad(variable);
       execution_result()->SetResultInAccumulator();
       break;
     }
     case VariableLocation::PARAMETER: {
       // The parameter indices are shifted by 1 (receiver is variable
       // index -1 but is parameter index 0 in BytecodeArrayBuilder).
       Register source = builder()->Parameter(variable->index() + 1);
       builder()->LoadAccumulatorWithRegister(source);
-      BuildHoleCheckForVariableLoad(mode, variable->name());
+      BuildHoleCheckForVariableLoad(variable);
       execution_result()->SetResultInAccumulator();
       break;
     }
     case VariableLocation::GLOBAL:
     case VariableLocation::UNALLOCATED: {
       builder()->LoadGlobal(feedback_index(slot), typeof_mode);
       execution_result()->SetResultInAccumulator();
       break;
     }
     case VariableLocation::CONTEXT: {
@@ skipping 13 matching lines @@
             ->LoadAccumulatorWithRegister(execution_context()->reg())
             .StoreAccumulatorInRegister(context_reg);
         for (int i = 0; i < depth; ++i) {
           builder()
               ->LoadContextSlot(context_reg, Context::PREVIOUS_INDEX)
               .StoreAccumulatorInRegister(context_reg);
         }
       }
 
       builder()->LoadContextSlot(context_reg, variable->index());
-      BuildHoleCheckForVariableLoad(mode, variable->name());
+      BuildHoleCheckForVariableLoad(variable);
       execution_result()->SetResultInAccumulator();
       break;
     }
     case VariableLocation::LOOKUP: {
       builder()->LoadLookupSlot(variable->name(), typeof_mode);
       execution_result()->SetResultInAccumulator();
       break;
     }
   }
 }
@@ skipping 1356 matching lines @@
   return execution_context()->scope()->language_mode();
 }
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return TypeFeedbackVector::GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8