[turbofan] Add initial support for global specialization.

src/compiler/js-global-specialization.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/compiler/js-global-specialization.h"
+
+#include "src/compilation-dependencies.h"
+#include "src/compiler/access-builder.h"
+#include "src/compiler/js-graph.h"
+#include "src/compiler/js-operator.h"
+#include "src/contexts.h"
+#include "src/lookup.h"
+#include "src/objects-inl.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+JSGlobalSpecialization::JSGlobalSpecialization(
+    Editor* editor, JSGraph* jsgraph, Flags flags,
+    Handle<GlobalObject> global_object, CompilationDependencies* dependencies)
+    : AdvancedReducer(editor),
+      jsgraph_(jsgraph),
+      flags_(flags),
+      global_object_(global_object),
+      dependencies_(dependencies),
+      simplified_(graph()->zone()) {}
+
+
+Reduction JSGlobalSpecialization::Reduce(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kJSLoadGlobal:
+      return ReduceJSLoadGlobal(node);
+    case IrOpcode::kJSStoreGlobal:
+      return ReduceJSStoreGlobal(node);
+    default:
+      break;
+  }
+  return NoChange();
+}
+
+
+Reduction JSGlobalSpecialization::ReduceJSLoadGlobal(Node* node) {
+  DCHECK_EQ(IrOpcode::kJSLoadGlobal, node->opcode());
+  Handle<Name> name = LoadGlobalParametersOf(node->op()).name();
+  Node* effect = NodeProperties::GetEffectInput(node);
+
+  // Try to lookup the name on the script context table first (lexical scoping).
+  if (name->IsString()) {
+    Handle<ScriptContextTable> script_context_table(
+        global_object()->native_context()->script_context_table());
+    ScriptContextTable::LookupResult result;
+    if (ScriptContextTable::Lookup(script_context_table,
+                                   Handle<String>::cast(name), &result)) {
+      Handle<Context> script_context = ScriptContextTable::GetContext(
+          script_context_table, result.context_index);
+      if (script_context->is_the_hole(result.slot_index)) {
+        // TODO(bmeurer): Is this relevant in practice?
+        return NoChange();
+      }
+      Node* context = jsgraph()->Constant(script_context);
+      Node* value = effect = graph()->NewNode(
+          javascript()->LoadContext(0, result.slot_index,
+                                    IsImmutableVariableMode(result.mode)),
+          context, context, effect);
+      return Replace(node, value, effect);
+    }
+  }
+
+  // Lookup on the global object instead.
+  LookupIterator it(global_object(), name, LookupIterator::OWN);
+  if (it.state() == LookupIterator::DATA) {
+    return ReduceLoadFromPropertyCell(node, it.GetPropertyCell());
+  }
+
+  return NoChange();
+}
+
+
+Reduction JSGlobalSpecialization::ReduceJSStoreGlobal(Node* node) {
+  DCHECK_EQ(IrOpcode::kJSStoreGlobal, node->opcode());
+  Handle<Name> name = StoreGlobalParametersOf(node->op()).name();
+  Node* value = NodeProperties::GetValueInput(node, 2);
+  Node* effect = NodeProperties::GetEffectInput(node);
+  Node* control = NodeProperties::GetControlInput(node);
+
+  // Try to lookup the name on the script context table first (lexical scoping).
+  if (name->IsString()) {
+    Handle<ScriptContextTable> script_context_table(
+        global_object()->native_context()->script_context_table());
+    ScriptContextTable::LookupResult result;
+    if (ScriptContextTable::Lookup(script_context_table,
+                                   Handle<String>::cast(name), &result)) {
+      if (IsImmutableVariableMode(result.mode)) return NoChange();
+      Handle<Context> script_context = ScriptContextTable::GetContext(
+          script_context_table, result.context_index);
+      if (script_context->is_the_hole(result.slot_index)) {
+        // TODO(bmeurer): Is this relevant in practice?
+        return NoChange();
+      }
+      Node* context = jsgraph()->Constant(script_context);
+      effect =
+          graph()->NewNode(javascript()->StoreContext(0, result.slot_index),
+                           context, value, context, effect, control);
+      return Replace(node, value, effect, control);
+    }
+  }
+
+  // Lookup on the global object instead.
+  LookupIterator it(global_object(), name, LookupIterator::OWN);
+  if (it.state() == LookupIterator::DATA) {
+    return ReduceStoreToPropertyCell(node, it.GetPropertyCell());
+  }
+
+  return NoChange();
+}
+
+
+Reduction JSGlobalSpecialization::ReduceLoadFromPropertyCell(
+    Node* node, Handle<PropertyCell> property_cell) {
+  Node* effect = NodeProperties::GetEffectInput(node);
+  Node* control = NodeProperties::GetControlInput(node);
+  // We only specialize global data property access.
+  PropertyDetails property_details = property_cell->property_details();
+  DCHECK_EQ(kData, property_details.kind());
+  Handle<Object> property_cell_value(property_cell->value(), isolate());
+  DCHECK(!property_cell_value->IsTheHole());
+  // Load from non-configurable, read-only data property on the global
+  // object can be constant-folded, even without deoptimization support.
+  if (!property_details.IsConfigurable() && property_details.IsReadOnly()) {
+    return Replace(node, property_cell_value);
+  }
+  // Load from constant/undefined global property can be constant-folded
+  // with deoptimization support, by adding a code dependency on the cell.
+  if ((property_details.cell_type() == PropertyCellType::kConstant ||
+       property_details.cell_type() == PropertyCellType::kUndefined) &&
+      (flags() & kDeoptimizationEnabled)) {
+    dependencies()->AssumePropertyCell(property_cell);
+    return Replace(node, property_cell_value);
+  }
+  // Not much we can do if we run the generic pipeline here.
+  if (!(flags() & kTypingEnabled)) return NoChange();
+  // Load from constant type global property can benefit from representation
+  // (and map) feedback with deoptimization support (requires code dependency).
+  if (property_details.cell_type() == PropertyCellType::kConstantType &&
+      (flags() & kDeoptimizationEnabled)) {
+    dependencies()->AssumePropertyCell(property_cell);
+    Type* property_cell_value_type = Type::Any();
+    switch (property_cell->GetConstantType()) {
+      case PropertyCellConstantType::kSmi:
+        property_cell_value_type = Type::Intersect(
+            Type::SignedSmall(), Type::TaggedSigned(), graph()->zone());
+        break;
+      case PropertyCellConstantType::kStableMap: {
+        // TODO(bmeurer): Determine type based on the map's instance type.
+        property_cell_value_type = Type::TaggedPointer();
+        break;
+      }
+    }
+    Node* value = effect = graph()->NewNode(
+        simplified()->LoadField(
+            AccessBuilder::ForPropertyCellValue(property_cell_value_type)),
+        jsgraph()->Constant(property_cell), effect, control);
+    return Replace(node, value, effect);
+  }
+  // Load from non-configurable, data property on the global can be lowered to
+  // a field load, even without deoptimization, because the property cannot be
+  // deleted or reconfigured to an accessor/interceptor property.
+  if (property_details.IsConfigurable()) {
+    // With deoptimization support, we can lower loads even from configurable
+    // data properties on the global object, by adding a code dependency on
+    // the cell.
+    if (!(flags() & kDeoptimizationEnabled)) return NoChange();
+    dependencies()->AssumePropertyCell(property_cell);
+  }
+  Node* value = effect = graph()->NewNode(
+      simplified()->LoadField(AccessBuilder::ForPropertyCellValue()),
+      jsgraph()->Constant(property_cell), effect, control);
+  return Replace(node, value, effect);
+}
+
+
+Reduction JSGlobalSpecialization::ReduceStoreToPropertyCell(
+    Node* node, Handle<PropertyCell> property_cell) {
+  Node* value = NodeProperties::GetValueInput(node, 2);
+  Node* effect = NodeProperties::GetEffectInput(node);
+  Node* control = NodeProperties::GetControlInput(node);
+  // We only specialize global data property access.
+  PropertyDetails property_details = property_cell->property_details();
+  DCHECK_EQ(kData, property_details.kind());
+  Handle<Object> property_cell_value(property_cell->value(), isolate());
+  DCHECK(!property_cell_value->IsTheHole());
+  // Don't even bother trying to lower stores to read-only data properties.
+  if (property_details.IsReadOnly()) return NoChange();
+  // Not much we can do if we run the generic pipeline here.
+  if (!(flags() & kTypingEnabled)) return NoChange();
+  // TODO(bmeurer): For now we deal only with cells in mutable state.
+  if (property_details.cell_type() != PropertyCellType::kMutable) {
+    return NoChange();
+  }
+  // Store to non-configurable, data property on the global can be lowered to
+  // a field store, even without deoptimization, because the property cannot be
+  // deleted or reconfigured to an accessor/interceptor property.
+  if (property_details.IsConfigurable()) {
+    // With deoptimization support, we can lower stores even to configurable
+    // data properties on the global object, by adding a code dependency on
+    // the cell.
+    if (!(flags() & kDeoptimizationEnabled)) return NoChange();
+    dependencies()->AssumePropertyCell(property_cell);
+  }
+  effect = graph()->NewNode(
+      simplified()->StoreField(AccessBuilder::ForPropertyCellValue()),
+      jsgraph()->Constant(property_cell), value, effect, control);
+  return Replace(node, value, effect, control);
+}
+
+
+Reduction JSGlobalSpecialization::Replace(Node* node, Handle<Object> value) {
+  if (value->IsConsString()) {
+    value = String::Flatten(Handle<String>::cast(value), TENURED);
+  }
+  return Replace(node, jsgraph()->Constant(value));
+}
+
+
+Graph* JSGlobalSpecialization::graph() const { return jsgraph()->graph(); }
+
+
+Isolate* JSGlobalSpecialization::isolate() const {
+  return jsgraph()->isolate();
+}
+
+
+JSOperatorBuilder* JSGlobalSpecialization::javascript() const {
+  return jsgraph()->javascript();
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8