[ignition] Eliminate hole checks where statically possible for loads and stores

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/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compilation-info.h"
@@ skipping 811 matching lines @@
 
       builder()
           ->LoadLiteral(variable->name())
           .StoreAccumulatorInRegister(name)
           .CallRuntime(Runtime::kDeclareEvalVar, name);
       break;
     }
     case VariableLocation::MODULE:
       if (variable->IsExport() && variable->binding_needs_init()) {
         builder()->LoadTheHole();
-        VisitVariableAssignment(variable, Token::INIT,
-                                FeedbackVectorSlot::Invalid());
+        BuildVariableAssignment(variable, Token::INIT,
+                                FeedbackVectorSlot::Invalid(), false);
       }
       // Nothing to do for imports.
       break;
   }
 }
 
 void BytecodeGenerator::VisitFunctionDeclaration(FunctionDeclaration* decl) {
   Variable* variable = decl->proxy()->var();
   DCHECK(variable->mode() == LET || variable->mode() == VAR);
   switch (variable->location()) {
     case VariableLocation::UNALLOCATED: {
       FeedbackVectorSlot slot = decl->proxy()->VariableFeedbackSlot();
       globals_builder()->AddFunctionDeclaration(slot, decl->fun());
       break;
     }
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL: {
       VisitForAccumulatorValue(decl->fun());
-      VisitVariableAssignment(variable, Token::INIT,
-                              FeedbackVectorSlot::Invalid());
+      BuildVariableAssignment(variable, Token::INIT,
+                              FeedbackVectorSlot::Invalid(), false);
       break;
     }
     case VariableLocation::CONTEXT: {
       DCHECK_EQ(0, execution_context()->ContextChainDepth(variable->scope()));
       VisitForAccumulatorValue(decl->fun());
       builder()->StoreContextSlot(execution_context()->reg(), variable->index(),
                                   0);
       break;
     }
     case VariableLocation::LOOKUP: {
       RegisterList args = register_allocator()->NewRegisterList(2);
       builder()
           ->LoadLiteral(variable->name())
           .StoreAccumulatorInRegister(args[0]);
       VisitForAccumulatorValue(decl->fun());
       builder()->StoreAccumulatorInRegister(args[1]).CallRuntime(
           Runtime::kDeclareEvalFunction, args);
       break;
     }
     case VariableLocation::MODULE:
       DCHECK_EQ(variable->mode(), LET);
       DCHECK(variable->IsExport());
       VisitForAccumulatorValue(decl->fun());
-      VisitVariableAssignment(variable, Token::INIT,
-                              FeedbackVectorSlot::Invalid());
+      BuildVariableAssignment(variable, Token::INIT,
+                              FeedbackVectorSlot::Invalid(), false);
       break;
   }
 }
 
 void BytecodeGenerator::VisitModuleNamespaceImports() {
   if (!scope()->is_module_scope()) return;
 
   RegisterAllocationScope register_scope(this);
   Register module_request = register_allocator()->NewRegister();
 
   ModuleDescriptor* descriptor = scope()->AsModuleScope()->module();
   for (auto entry : descriptor->namespace_imports()) {
     builder()
         ->LoadLiteral(Smi::FromInt(entry->module_request))
         .StoreAccumulatorInRegister(module_request)
         .CallRuntime(Runtime::kGetModuleNamespace, module_request);
     Variable* var = scope()->LookupLocal(entry->local_name);
     DCHECK_NOT_NULL(var);
-    VisitVariableAssignment(var, Token::INIT, FeedbackVectorSlot::Invalid());
+    BuildVariableAssignment(var, Token::INIT, FeedbackVectorSlot::Invalid(),
+                            false);
   }
 }
 
 void BytecodeGenerator::VisitDeclarations(
     ZoneList<Declaration*>* declarations) {
   RegisterAllocationScope register_scope(this);
   DCHECK(globals_builder()->empty());
   for (int i = 0; i < declarations->length(); i++) {
     RegisterAllocationScope register_scope(this);
     Visit(declarations->at(i));
@@ skipping 232 matching lines @@
 void BytecodeGenerator::VisitForInAssignment(Expression* expr,
                                              FeedbackVectorSlot slot) {
   DCHECK(expr->IsValidReferenceExpression());
 
   // Evaluate assignment starting with the value to be stored in the
   // accumulator.
   Property* property = expr->AsProperty();
   LhsKind assign_type = Property::GetAssignType(property);
   switch (assign_type) {
     case VARIABLE: {
-      Variable* variable = expr->AsVariableProxy()->var();
-      VisitVariableAssignment(variable, Token::ASSIGN, slot);
+      VariableProxy* proxy = expr->AsVariableProxy();
+      BuildVariableAssignment(proxy->var(), Token::ASSIGN, slot,
+                              proxy->needs_hole_check());
       break;
     }
     case NAMED_PROPERTY: {
       RegisterAllocationScope register_scope(this);
       Register value = register_allocator()->NewRegister();
       builder()->StoreAccumulatorInRegister(value);
       Register object = VisitForRegisterValue(property->obj());
       Handle<String> name = property->key()->AsLiteral()->AsPropertyName();
       builder()->LoadAccumulatorWithRegister(value);
       builder()->StoreNamedProperty(object, name, feedback_index(slot),
@@ skipping 226 matching lines @@
   FeedbackVectorSlot slot = expr->PrototypeSlot();
   builder()
       ->StoreAccumulatorInRegister(literal)
       .LoadNamedProperty(literal, prototype_string(), feedback_index(slot))
       .StoreAccumulatorInRegister(prototype);
 
   VisitClassLiteralProperties(expr, literal, prototype);
   builder()->CallRuntime(Runtime::kToFastProperties, literal);
   // Assign to class variable.
   if (expr->class_variable_proxy() != nullptr) {
-    Variable* var = expr->class_variable_proxy()->var();
+    VariableProxy* proxy = expr->class_variable_proxy();
     FeedbackVectorSlot slot = expr->NeedsProxySlot()
                                   ? expr->ProxySlot()
                                   : FeedbackVectorSlot::Invalid();
-    VisitVariableAssignment(var, Token::INIT, slot);
+    BuildVariableAssignment(proxy->var(), Token::INIT, slot, false);
   }
 }
 
 void BytecodeGenerator::VisitClassLiteralForRuntimeDefinition(
     ClassLiteral* expr) {
   RegisterAllocationScope register_scope(this);
   RegisterList args = register_allocator()->NewRegisterList(4);
   VisitForAccumulatorValueOrTheHole(expr->extends());
   builder()->StoreAccumulatorInRegister(args[0]);
   VisitForRegisterValue(expr->constructor(), args[1]);
@@ skipping 353 matching lines @@
   }
 
   if (!literal_in_accumulator) {
     // Restore literal array into accumulator.
     builder()->LoadAccumulatorWithRegister(literal);
   }
 }
 
 void BytecodeGenerator::VisitVariableProxy(VariableProxy* proxy) {
   builder()->SetExpressionPosition(proxy);
-  VisitVariableLoad(proxy->var(), proxy->VariableFeedbackSlot());
+  BuildVariableLoad(proxy->var(), proxy->VariableFeedbackSlot(),
+                    proxy->needs_hole_check());
 }
 
-void BytecodeGenerator::BuildHoleCheckForVariableLoad(Variable* variable) {
-  if (variable->binding_needs_init()) {
-    BuildThrowIfHole(variable->name());
-  }
-}
-
-void BytecodeGenerator::VisitVariableLoad(Variable* variable,
+void BytecodeGenerator::BuildVariableLoad(Variable* variable,
                                           FeedbackVectorSlot slot,
+                                          bool needs_hole_check,
                                           TypeofMode typeof_mode) {
   switch (variable->location()) {
     case VariableLocation::LOCAL: {
       Register source(Register(variable->index()));
       // We need to load the variable into the accumulator, even when in a
       // VisitForRegisterScope, in order to avoid register aliasing if
       // subsequent expressions assign to the same variable.
       builder()->LoadAccumulatorWithRegister(source);
-      BuildHoleCheckForVariableLoad(variable);
+      if (needs_hole_check) BuildThrowIfHole(variable->name());
       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);
       // We need to load the variable into the accumulator, even when in a
       // VisitForRegisterScope, in order to avoid register aliasing if
       // subsequent expressions assign to the same variable.
       builder()->LoadAccumulatorWithRegister(source);
-      BuildHoleCheckForVariableLoad(variable);
+      if (needs_hole_check) BuildThrowIfHole(variable->name());
       break;
     }
     case VariableLocation::UNALLOCATED: {
       builder()->LoadGlobal(feedback_index(slot), typeof_mode);
       break;
     }
     case VariableLocation::CONTEXT: {
       int depth = execution_context()->ContextChainDepth(variable->scope());
       ContextScope* context = execution_context()->Previous(depth);
       Register context_reg;
       if (context) {
         context_reg = context->reg();
         depth = 0;
       } else {
         context_reg = execution_context()->reg();
       }
 
       builder()->LoadContextSlot(context_reg, variable->index(), depth);
-      BuildHoleCheckForVariableLoad(variable);
+      if (needs_hole_check) BuildThrowIfHole(variable->name());
       break;
     }
     case VariableLocation::LOOKUP: {
       switch (variable->mode()) {
         case DYNAMIC_LOCAL: {
           Variable* local_variable = variable->local_if_not_shadowed();
           int depth =
               execution_context()->ContextChainDepth(local_variable->scope());
           builder()->LoadLookupContextSlot(variable->name(), typeof_mode,
                                            local_variable->index(), depth);
-          BuildHoleCheckForVariableLoad(variable);
+          if (needs_hole_check) BuildThrowIfHole(variable->name());
           break;
         }
         case DYNAMIC_GLOBAL: {
           int depth = scope()->ContextChainLengthUntilOutermostSloppyEval();
           builder()->LoadLookupGlobalSlot(variable->name(), typeof_mode,
                                           feedback_index(slot), depth);
           break;
         }
         default:
           builder()->LoadLookupSlot(variable->name(), typeof_mode);
@@ skipping 14 matching lines @@
         auto it = descriptor->regular_imports().find(variable->raw_name());
         DCHECK(it != descriptor->regular_imports().end());
         RegisterList args = register_allocator()->NewRegisterList(2);
         builder()
             ->LoadLiteral(it->second->import_name->string())
             .StoreAccumulatorInRegister(args[0])
             .LoadLiteral(Smi::FromInt(it->second->module_request))
             .StoreAccumulatorInRegister(args[1])
             .CallRuntime(Runtime::kLoadModuleImport, args);
       }
-      BuildHoleCheckForVariableLoad(variable);
+      if (needs_hole_check) BuildThrowIfHole(variable->name());
       break;
     }
   }
 }
 
-void BytecodeGenerator::VisitVariableLoadForAccumulatorValue(
-    Variable* variable, FeedbackVectorSlot slot, TypeofMode typeof_mode) {
+void BytecodeGenerator::BuildVariableLoadForAccumulatorValue(
+    Variable* variable, FeedbackVectorSlot slot, bool needs_hole_check,
+    TypeofMode typeof_mode) {
   ValueResultScope accumulator_result(this);
-  VisitVariableLoad(variable, slot, typeof_mode);
+  BuildVariableLoad(variable, slot, needs_hole_check, typeof_mode);
 }
 
 void BytecodeGenerator::BuildReturn() {
   if (FLAG_trace) {
     RegisterAllocationScope register_scope(this);
     Register result = register_allocator()->NewRegister();
     // Runtime returns {result} value, preserving accumulator.
     builder()->StoreAccumulatorInRegister(result).CallRuntime(
         Runtime::kTraceExit, result);
   }
@@ skipping 48 matching lines @@
   } else {
     DCHECK(variable->is_this() && variable->mode() == CONST &&
            op == Token::INIT);
     // Perform an initialization check for 'this'. 'this' variable is the
     // only variable able to trigger bind operations outside the TDZ
     // via 'super' calls.
     BuildThrowIfNotHole(variable->name());
   }
 }
 
-void BytecodeGenerator::VisitVariableAssignment(Variable* variable,
+void BytecodeGenerator::BuildVariableAssignment(Variable* variable,
                                                 Token::Value op,
-                                                FeedbackVectorSlot slot) {
+                                                FeedbackVectorSlot slot,
+                                                bool needs_hole_check) {
   VariableMode mode = variable->mode();
   RegisterAllocationScope assignment_register_scope(this);
   BytecodeLabel end_label;
-  bool hole_check_required =
-      variable->binding_needs_init() &&
-      (op != Token::INIT || (mode == CONST && variable->is_this()));
   switch (variable->location()) {
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL: {
       Register destination;
       if (VariableLocation::PARAMETER == variable->location()) {
         destination = Register(builder()->Parameter(variable->index() + 1));
       } else {
         destination = Register(variable->index());
       }
 
-      if (hole_check_required) {
+      if (needs_hole_check) {
         // Load destination to check for hole.
         Register value_temp = register_allocator()->NewRegister();
         builder()
             ->StoreAccumulatorInRegister(value_temp)
             .LoadAccumulatorWithRegister(destination);
 
         BuildHoleCheckForVariableAssignment(variable, op);
         builder()->LoadAccumulatorWithRegister(value_temp);
       }
 
@@ skipping 14 matching lines @@
       ContextScope* context = execution_context()->Previous(depth);
       Register context_reg;
 
       if (context) {
         context_reg = context->reg();
         depth = 0;
       } else {
         context_reg = execution_context()->reg();
       }
 
-      if (hole_check_required) {
+      if (needs_hole_check) {
         // Load destination to check for hole.
         Register value_temp = register_allocator()->NewRegister();
         builder()
             ->StoreAccumulatorInRegister(value_temp)
             .LoadContextSlot(context_reg, variable->index(), depth);
 
         BuildHoleCheckForVariableAssignment(variable, op);
         builder()->LoadAccumulatorWithRegister(value_temp);
       }
 
@@ skipping 87 matching lines @@
     }
   }
 
   // Evaluate the value and potentially handle compound assignments by loading
   // the left-hand side value and performing a binary operation.
   if (expr->is_compound()) {
     Register old_value = register_allocator()->NewRegister();
     switch (assign_type) {
       case VARIABLE: {
         VariableProxy* proxy = expr->target()->AsVariableProxy();
-        VisitVariableLoad(proxy->var(), proxy->VariableFeedbackSlot());
+        BuildVariableLoad(proxy->var(), proxy->VariableFeedbackSlot(),
+                          proxy->needs_hole_check());
         builder()->StoreAccumulatorInRegister(old_value);
         break;
       }
       case NAMED_PROPERTY: {
         FeedbackVectorSlot slot = property->PropertyFeedbackSlot();
         builder()
             ->LoadNamedProperty(object, name, feedback_index(slot))
             .StoreAccumulatorInRegister(old_value);
         break;
       }
@@ skipping 28 matching lines @@
                                feedback_index(slot));
   } else {
     VisitForAccumulatorValue(expr->value());
   }
 
   // Store the value.
   builder()->SetExpressionPosition(expr);
   FeedbackVectorSlot slot = expr->AssignmentSlot();
   switch (assign_type) {
     case VARIABLE: {
-      // TODO(oth): The VisitVariableAssignment() call is hard to reason about.
+      // TODO(oth): The BuildVariableAssignment() call is hard to reason about.
       // Is the value in the accumulator safe? Yes, but scary.
-      Variable* variable = expr->target()->AsVariableProxy()->var();
-      VisitVariableAssignment(variable, expr->op(), slot);
+      VariableProxy* proxy = expr->target()->AsVariableProxy();
+      BuildVariableAssignment(proxy->var(), expr->op(), slot,
+                              proxy->needs_hole_check());
       break;
     }
     case NAMED_PROPERTY:
       builder()->StoreNamedProperty(object, name, feedback_index(slot),
                                     language_mode());
       break;
     case KEYED_PROPERTY:
       builder()->StoreKeyedProperty(object, key, feedback_index(slot),
                                     language_mode());
       break;
@@ skipping 205 matching lines @@
       builder()->StoreAccumulatorInRegister(receiver);
       VisitPropertyLoadForAccumulator(receiver, property);
       builder()->StoreAccumulatorInRegister(callee);
       break;
     }
     case Call::GLOBAL_CALL: {
       // Receiver is undefined for global calls.
       builder()->LoadUndefined().StoreAccumulatorInRegister(receiver);
       // Load callee as a global variable.
       VariableProxy* proxy = callee_expr->AsVariableProxy();
-      VisitVariableLoadForAccumulatorValue(proxy->var(),
-                                           proxy->VariableFeedbackSlot());
+      BuildVariableLoadForAccumulatorValue(proxy->var(),
+                                           proxy->VariableFeedbackSlot(),
+                                           proxy->needs_hole_check());
       builder()->StoreAccumulatorInRegister(callee);
       break;
     }
     case Call::LOOKUP_SLOT_CALL:
     case Call::POSSIBLY_EVAL_CALL: {
       if (callee_expr->AsVariableProxy()->var()->IsLookupSlot()) {
         RegisterAllocationScope inner_register_scope(this);
         Register name = register_allocator()->NewRegister();
 
         // Call %LoadLookupSlotForCall to get the callee and receiver.
@@ skipping 136 matching lines @@
 void BytecodeGenerator::VisitVoid(UnaryOperation* expr) {
   VisitForEffect(expr->expression());
   builder()->LoadUndefined();
 }
 
 void BytecodeGenerator::VisitTypeOf(UnaryOperation* expr) {
   if (expr->expression()->IsVariableProxy()) {
     // Typeof does not throw a reference error on global variables, hence we
     // perform a non-contextual load in case the operand is a variable proxy.
     VariableProxy* proxy = expr->expression()->AsVariableProxy();
-    VisitVariableLoadForAccumulatorValue(
-        proxy->var(), proxy->VariableFeedbackSlot(), INSIDE_TYPEOF);
+    BuildVariableLoadForAccumulatorValue(
+        proxy->var(), proxy->VariableFeedbackSlot(), proxy->needs_hole_check(),
+        INSIDE_TYPEOF);
   } else {
     VisitForAccumulatorValue(expr->expression());
   }
   builder()->TypeOf();
 }
 
 void BytecodeGenerator::VisitNot(UnaryOperation* expr) {
   if (execution_result()->IsEffect()) {
     VisitForEffect(expr->expression());
   } else if (execution_result()->IsTest()) {
@@ skipping 103 matching lines @@
 
   bool is_postfix = expr->is_postfix() && !execution_result()->IsEffect();
 
   // Evaluate LHS expression and get old value.
   Register object, key, old_value;
   RegisterList super_property_args;
   Handle<String> name;
   switch (assign_type) {
     case VARIABLE: {
       VariableProxy* proxy = expr->expression()->AsVariableProxy();
-      VisitVariableLoadForAccumulatorValue(proxy->var(),
-                                           proxy->VariableFeedbackSlot());
+      BuildVariableLoadForAccumulatorValue(proxy->var(),
+                                           proxy->VariableFeedbackSlot(),
+                                           proxy->needs_hole_check());
       break;
     }
     case NAMED_PROPERTY: {
       FeedbackVectorSlot slot = property->PropertyFeedbackSlot();
       object = VisitForRegisterValue(property->obj());
       name = property->key()->AsLiteral()->AsPropertyName();
       builder()->LoadNamedProperty(object, name, feedback_index(slot));
       break;
     }
     case KEYED_PROPERTY: {
@@ skipping 42 matching lines @@
 
   // Perform +1/-1 operation.
   FeedbackVectorSlot slot = expr->CountBinaryOpFeedbackSlot();
   builder()->CountOperation(expr->binary_op(), feedback_index(slot));
 
   // Store the value.
   builder()->SetExpressionPosition(expr);
   FeedbackVectorSlot feedback_slot = expr->CountSlot();
   switch (assign_type) {
     case VARIABLE: {
-      Variable* variable = expr->expression()->AsVariableProxy()->var();
-      VisitVariableAssignment(variable, expr->op(), feedback_slot);
+      VariableProxy* proxy = expr->expression()->AsVariableProxy();
+      BuildVariableAssignment(proxy->var(), expr->op(), feedback_slot,
+                              proxy->needs_hole_check());
       break;
     }
     case NAMED_PROPERTY: {
       builder()->StoreNamedProperty(object, name, feedback_index(feedback_slot),
                                     language_mode());
       break;
     }
     case KEYED_PROPERTY: {
       builder()->StoreKeyedProperty(object, key, feedback_index(feedback_slot),
                                     language_mode());
@@ skipping 271 matching lines @@
 
   DCHECK(variable->IsContextSlot() || variable->IsStackAllocated());
 
   // Allocate and initialize a new arguments object and assign to the
   // {arguments} variable.
   CreateArgumentsType type =
       is_strict(language_mode()) || !info()->has_simple_parameters()
           ? CreateArgumentsType::kUnmappedArguments
           : CreateArgumentsType::kMappedArguments;
   builder()->CreateArguments(type);
-  VisitVariableAssignment(variable, Token::ASSIGN,
-                          FeedbackVectorSlot::Invalid());
+  BuildVariableAssignment(variable, Token::ASSIGN,
+                          FeedbackVectorSlot::Invalid(), false);
 }
 
 void BytecodeGenerator::VisitRestArgumentsArray(Variable* rest) {
   if (rest == nullptr) return;
 
   // Allocate and initialize a new rest parameter and assign to the {rest}
   // variable.
   builder()->CreateArguments(CreateArgumentsType::kRestParameter);
   DCHECK(rest->IsContextSlot() || rest->IsStackAllocated());
-  VisitVariableAssignment(rest, Token::ASSIGN, FeedbackVectorSlot::Invalid());
+  BuildVariableAssignment(rest, Token::ASSIGN, FeedbackVectorSlot::Invalid(),
+                          false);
 }
 
 void BytecodeGenerator::VisitThisFunctionVariable(Variable* variable) {
   if (variable == nullptr) return;
 
   // Store the closure we were called with in the given variable.
   builder()->LoadAccumulatorWithRegister(Register::function_closure());
-  VisitVariableAssignment(variable, Token::INIT, FeedbackVectorSlot::Invalid());
+  BuildVariableAssignment(variable, Token::INIT, FeedbackVectorSlot::Invalid(),
+                          false);
 }
 
 void BytecodeGenerator::VisitNewTargetVariable(Variable* variable) {
   if (variable == nullptr) return;
 
   // Store the new target we were called with in the given variable.
   builder()->LoadAccumulatorWithRegister(Register::new_target());
-  VisitVariableAssignment(variable, Token::INIT, FeedbackVectorSlot::Invalid());
+  BuildVariableAssignment(variable, Token::INIT, FeedbackVectorSlot::Invalid(),
+                          false);
 
   // TODO(mstarzinger): The <new.target> register is not set by the deoptimizer
   // and we need to make sure {BytecodeRegisterOptimizer} flushes its state
   // before a local variable containing the <new.target> is used. Using a label
   // as below flushes the entire pipeline, we should be more specific here.
   BytecodeLabel flush_state_label;
   builder()->Bind(&flush_state_label);
 }
 
 void BytecodeGenerator::VisitFunctionClosureForContext() {
@@ skipping 110 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8