Generalize virtually dispatched scavenger to virtually dispatched specialized visitors.

src/objects-visiting.h

+// Copyright 2006-2009 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_OBJECTS_ITERATION_H_
+#define V8_OBJECTS_ITERATION_H_
+
+// This file provides base classes and auxiliary methods for defining
+// static object visitors used during GC.
+// Visiting HeapObject body with a normal ObjectVisitor requires performing
+// two switches on object's instance type to determine object size and layout
+// and one or more virtual method calls on visitor itself.
+// Static visitor is different: it provides a dispatch table which contains
+// pointers to specialized visit functions. Each map has the visitor_id
+// field which contains an index of specialized visitor to use.
+
+namespace v8 {
+namespace internal {
+
+
+// Base class for all static visitors.
+class StaticVisitorBase : public AllStatic {
+ public:
+  enum VisitorId {
+    kVisitSeqAsciiString = 0,
+    kVisitSeqTwoByteString,
+    kVisitShortcutCandidate,
+    kVisitByteArray,
+    kVisitFixedArray,
+
+    // For data objects, JS objects and structs along with generic visitor we
+    // provide visitors specialized by object size in words.
+    // Method GetVisitorIdForSize should be used to calculate visitor id for
+    // given instance size.
+
+    kVisitDataObject,
+    kVisitDataObject2 = kVisitDataObject,
+    kVisitDataObject3,
+    kVisitDataObject4,
+    kVisitDataObject5,
+    kVisitDataObject6,
+    kVisitDataObject7,
+    kVisitDataObject8,
+    kVisitDataObject9,
+    kVisitDataObjectGeneric,
+
+    kVisitJSObject,
+    kVisitJSObject2 = kVisitJSObject,
+    kVisitJSObject3,
+    kVisitJSObject4,
+    kVisitJSObject5,
+    kVisitJSObject6,
+    kVisitJSObject7,
+    kVisitJSObject8,
+    kVisitJSObject9,
+    kVisitJSObjectGeneric,
+
+    kVisitStruct,
+    kVisitStruct2 = kVisitStruct,
+    kVisitStruct3,
+    kVisitStruct4,
+    kVisitStruct5,
+    kVisitStruct6,
+    kVisitStruct7,
+    kVisitStruct8,
+    kVisitStruct9,
+    kVisitStructGeneric,
+
+    kVisitConsString,
+    kVisitOddball,
+    kVisitCode,
+    kVisitMap,
+    kVisitPropertyCell,
+    kVisitSharedFunctionInfo,
+
+    kVisitorIdCount,
+    kMinObjectSizeInWords = 2
+  };
+
+  // Determine which specialized visitor should be used for given instance type
+  // and instance type.
+  static VisitorId GetVisitorId(int instance_type, int instance_size);
+
+  static VisitorId GetVisitorId(Map* map) {
+    return GetVisitorId(map->instance_type(), map->instance_size());
+  }
+
+  // For visitors that allow specialization by size calculate VisitorId based
+  // on size, base visitor id and generic visitor id.
+  static VisitorId GetVisitorIdForSize(VisitorId base,
+                                       VisitorId generic,
+                                       int object_size) {
+    ASSERT((base == kVisitDataObject) ||
+           (base == kVisitStruct) ||
+           (base == kVisitJSObject));
+    ASSERT(IsAligned(object_size, kPointerSize));
+    ASSERT(kMinObjectSizeInWords * kPointerSize <= object_size);
+    ASSERT(object_size < Page::kMaxHeapObjectSize);
+
+    const VisitorId specialization = static_cast<VisitorId>(
+        base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords);
+
+    return Min(specialization, generic);
+  }
+};
+
+
+template<typename Callback>
+class VisitorDispatchTable {
+ public:
+  inline Callback GetVisitor(Map* map) {
+    return callbacks_[map->visitor_id()];
+  }
+
+  void Register(StaticVisitorBase::VisitorId id, Callback callback) {
+    ASSERT((0 <= id) && (id < StaticVisitorBase::kVisitorIdCount));
+    callbacks_[id] = callback;
+  }
+
+  template<typename Visitor,
+           StaticVisitorBase::VisitorId base,
+           StaticVisitorBase::VisitorId generic,
+           int object_size_in_words>
+  void RegisterSpecialization() {
+    static const int size = object_size_in_words * kPointerSize;
+    Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size),
+             &Visitor::template VisitSpecialized<size>);
+  }
+
+
+  template<typename Visitor,
+           StaticVisitorBase::VisitorId base,
+           StaticVisitorBase::VisitorId generic>
+  void RegisterSpecializations() {
+    STATIC_ASSERT(
+        (generic - base + StaticVisitorBase::kMinObjectSizeInWords) == 10);
+    RegisterSpecialization<Visitor, base, generic, 2>();
+    RegisterSpecialization<Visitor, base, generic, 3>();
+    RegisterSpecialization<Visitor, base, generic, 4>();
+    RegisterSpecialization<Visitor, base, generic, 5>();
+    RegisterSpecialization<Visitor, base, generic, 6>();
+    RegisterSpecialization<Visitor, base, generic, 7>();
+    RegisterSpecialization<Visitor, base, generic, 8>();
+    RegisterSpecialization<Visitor, base, generic, 9>();
+    Register(generic, &Visitor::Visit);
+  }
+
+ private:
+  Callback callbacks_[StaticVisitorBase::kVisitorIdCount];
+};
+
+
+template<typename StaticVisitor>
+class BodyVisitorBase : public AllStatic {
+ public:
+  static inline void IteratePointers(HeapObject* object,
+                                     int start_offset,
+                                     int end_offset) {
+    Object** start_slot = reinterpret_cast<Object**>(object->address() +
+                                                     start_offset);
+    Object** end_slot = reinterpret_cast<Object**>(object->address() +
+                                                   end_offset);
+    StaticVisitor::VisitPointers(start_slot, end_slot);
+  }
+};
+
+
+template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
+class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
+ public:
+  static inline ReturnType Visit(Map* map, HeapObject* object) {
+    int object_size = BodyDescriptor::SizeOf(map, object);
+    IteratePointers(object, BodyDescriptor::kStartOffset, object_size);
+    return static_cast<ReturnType>(object_size);
+  }
+
+  template<int object_size>
+  static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
+    IteratePointers(object, BodyDescriptor::kStartOffset, object_size);
+    return static_cast<ReturnType>(object_size);
+  }
+};
+
+
+template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
+class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
+ public:
+  static inline ReturnType Visit(Map* map, HeapObject* object) {
+    IteratePointers(object,
+                    BodyDescriptor::kStartOffset,
+                    BodyDescriptor::kEndOffset);
+    return static_cast<ReturnType>(BodyDescriptor::kSize);
+  }
+};
+
+
+// Base class for visitors used for a linear new space iteration.
+// IterateBody returns size of visited object.
+// Certain types of objects (i.e. Code objects) are not handled
+// by dispatch table of this visitor because they cannot appear
+// in the new space.
+//
+// This class is intended to be used in the following way:
+//
+//   class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
+//     ...
+//   }
+//
+// This is an example of Curiously recurring template pattern
+// (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
+// We use CRTP to guarantee aggressive compile time optimizations (i.e.
+// inlining and specialization of StaticVisitor::VisitPointers methods).
+template<typename StaticVisitor>
+class StaticNewSpaceVisitor : public StaticVisitorBase {
+ public:
+  static void Initialize() {
+    table_.Register(kVisitShortcutCandidate,
+                    &FixedBodyVisitor<StaticVisitor,
+                                      ConsString::BodyDescriptor,
+                                      int>::Visit);
+
+    table_.Register(kVisitConsString,
+                    &FixedBodyVisitor<StaticVisitor,
+                                      ConsString::BodyDescriptor,
+                                      int>::Visit);
+
+    table_.Register(kVisitFixedArray,
+                    &FlexibleBodyVisitor<StaticVisitor,
+                                         FixedArray::BodyDescriptor,
+                                         int>::Visit);
+
+    table_.Register(kVisitByteArray, &VisitByteArray);
+
+    table_.Register(kVisitSharedFunctionInfo,
+                    &FixedBodyVisitor<StaticVisitor,
+                                      SharedFunctionInfo::BodyDescriptor,
+                                      int>::Visit);
+
+    table_.Register(kVisitSeqAsciiString, &VisitSeqAsciiString);
+
+    table_.Register(kVisitSeqTwoByteString, &VisitSeqTwoByteString);
+
+    table_.RegisterSpecializations<DataObjectVisitor,
+                                   kVisitDataObject,
+                                   kVisitDataObjectGeneric>();
+    table_.RegisterSpecializations<JSObjectVisitor,
+                                   kVisitJSObject,
+                                   kVisitJSObjectGeneric>();
+    table_.RegisterSpecializations<StructVisitor,
+        kVisitStruct,
+        kVisitStructGeneric>();
+  }
+
+  static inline int IterateBody(Map* map, HeapObject* obj) {
+    return table_.GetVisitor(map)(map, obj);
+  }
+
+  static inline void VisitPointers(Object** start, Object** end) {
+    for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(p);
+  }
+
+ private:
+  static inline int VisitByteArray(Map* map, HeapObject* object) {
+    return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
+  }
+
+  static inline int VisitSeqAsciiString(Map* map, HeapObject* object) {
+    return SeqAsciiString::cast(object)->
+        SeqAsciiStringSize(map->instance_type());
+  }
+
+  static inline int VisitSeqTwoByteString(Map* map, HeapObject* object) {
+    return SeqTwoByteString::cast(object)->
+        SeqTwoByteStringSize(map->instance_type());
+  }
+
+  class DataObjectVisitor {
+   public:
+    template<int object_size>
+    static inline int VisitSpecialized(Map* map, HeapObject* object) {
+      return object_size;
+    }
+
+    static inline int Visit(Map* map, HeapObject* object) {
+      return map->instance_size();
+    }
+  };
+
+  typedef FlexibleBodyVisitor<StaticVisitor,
+                              StructBodyDescriptor,
+                              int> StructVisitor;
+
+  typedef FlexibleBodyVisitor<StaticVisitor,
+                              JSObject::BodyDescriptor,
+                              int> JSObjectVisitor;
+
+  typedef int (*Callback)(Map* map, HeapObject* object);
+
+  static VisitorDispatchTable<Callback> table_;
+};
+
+
+template<typename StaticVisitor>
+VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
+  StaticNewSpaceVisitor<StaticVisitor>::table_;
+
+
+void Code::CodeIterateBody(ObjectVisitor* v) {
+  int mode_mask = RelocInfo::kCodeTargetMask |
+                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
+                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
+                  RelocInfo::ModeMask(RelocInfo::JS_RETURN) |
+                  RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT) |
+                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);
+
+  // Use the relocation info pointer before it is visited by
+  // the heap compaction in the next statement.
+  RelocIterator it(this, mode_mask);
+
+  IteratePointers(v,
+                  kRelocationInfoOffset,
+                  kRelocationInfoOffset + kPointerSize);
+
+  for (; !it.done(); it.next()) {
+    it.rinfo()->Visit(v);
+  }
+}
+
+
+template<typename StaticVisitor>
+void Code::CodeIterateBody() {
+  int mode_mask = RelocInfo::kCodeTargetMask |
+                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
+                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
+                  RelocInfo::ModeMask(RelocInfo::JS_RETURN) |
+                  RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT) |
+                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);
+
+  // Use the relocation info pointer before it is visited by
+  // the heap compaction in the next statement.
+  RelocIterator it(this, mode_mask);
+
+  StaticVisitor::VisitPointer(
+      reinterpret_cast<Object**>(this->address() + kRelocationInfoOffset));
+
+  for (; !it.done(); it.next()) {
+    it.rinfo()->Visit<StaticVisitor>();
+  }
+}
+
+
+} }  // namespace v8::internal
+
+#endif  // V8_OBJECTS_ITERATION_H_