[ptr-compr][cleanup] Introduce TaggedField<T, kOffset> template

It will allow us to use knowledge about the type of field during value
decompression upon field read.

Use the new class for HeapObject::MapField.

Bug: v8:9353
Change-Id: I1368426ec2e25fcec3af8d5cccd7a78d80423e72
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1658150
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62184}

BUILD.gn

@@ -2601,6 +2601,8 @@ v8_source_set("v8_base_without_compiler") {
     "src/objects/string.h",
     "src/objects/struct-inl.h",
     "src/objects/struct.h",
+    "src/objects/tagged-field-inl.h",
+    "src/objects/tagged-field.h",
     "src/objects/tagged-impl-inl.h",
     "src/objects/tagged-impl.cc",
     "src/objects/tagged-impl.h",

src/common/ptr-compr-inl.h

@@ -25,8 +25,12 @@ V8_INLINE Address GetIsolateRoot(TOnHeapAddress on_heap_addr);
 
 template <>
 V8_INLINE Address GetIsolateRoot<Address>(Address on_heap_addr) {
+  // We subtract 1 here in order to let the compiler generate addition of 32-bit
+  // signed constant instead of 64-bit constant (the problem is that 2Gb looks
+  // like a negative 32-bit value). It's correct because we will never use
+  // leftmost address of V8 heap as |on_heap_addr|.
   return RoundDown<kPtrComprIsolateRootAlignment>(on_heap_addr +
-                                                  kPtrComprIsolateRootBias);
+                                                  kPtrComprIsolateRootBias - 1);
 }
 
 template <>

src/heap/mark-compact.cc

@@ -1366,8 +1366,7 @@ class EvacuateNewSpaceVisitor final : public EvacuateVisitorBase {
     if (map.visitor_id() == kVisitThinString) {
       HeapObject actual = ThinString::cast(object).unchecked_actual();
       if (MarkCompactCollector::IsOnEvacuationCandidate(actual)) return false;
-      object.map_slot().Relaxed_Store(
-          MapWord::FromForwardingAddress(actual).ToMap());
+      object.set_map_word(MapWord::FromForwardingAddress(actual));
       return true;
     }
     // TODO(mlippautz): Handle ConsString.

src/heap/scavenger-inl.h

@@ -109,9 +109,8 @@ bool Scavenger::MigrateObject(Map map, HeapObject source, HeapObject target,
   heap()->CopyBlock(target.address() + kTaggedSize,
                     source.address() + kTaggedSize, size - kTaggedSize);
 
-  Object old = source.map_slot().Release_CompareAndSwap(
-      map, MapWord::FromForwardingAddress(target).ToMap());
-  if (old != map) {
+  if (!source.synchronized_compare_and_swap_map_word(
+          MapWord::FromMap(map), MapWord::FromForwardingAddress(target))) {
     // Other task migrated the object.
     return false;
   }
@@ -215,8 +214,8 @@ bool Scavenger::HandleLargeObject(Map map, HeapObject object, int object_size,
           MemoryChunk::FromHeapObject(object)->InNewLargeObjectSpace())) {
     DCHECK_EQ(NEW_LO_SPACE,
               MemoryChunk::FromHeapObject(object)->owner_identity());
-    if (object.map_slot().Release_CompareAndSwap(
-            map, MapWord::FromForwardingAddress(object).ToMap()) == map) {
+    if (object.synchronized_compare_and_swap_map_word(
+            MapWord::FromMap(map), MapWord::FromForwardingAddress(object))) {
       surviving_new_large_objects_.insert({object, map});
       promoted_size_ += object_size;
       if (object_fields == ObjectFields::kMaybePointers) {
@@ -313,8 +312,7 @@ SlotCallbackResult Scavenger::EvacuateShortcutCandidate(Map map,
     HeapObjectReference::Update(slot, first);
 
     if (!Heap::InYoungGeneration(first)) {
-      object.map_slot().Release_Store(
-          MapWord::FromForwardingAddress(first).ToMap());
+      object.synchronized_set_map_word(MapWord::FromForwardingAddress(first));
       return REMOVE_SLOT;
     }
 
@@ -323,16 +321,15 @@ SlotCallbackResult Scavenger::EvacuateShortcutCandidate(Map map,
       HeapObject target = first_word.ToForwardingAddress();
 
       HeapObjectReference::Update(slot, target);
-      object.map_slot().Release_Store(
-          MapWord::FromForwardingAddress(target).ToMap());
+      object.synchronized_set_map_word(MapWord::FromForwardingAddress(target));
       return Heap::InYoungGeneration(target) ? KEEP_SLOT : REMOVE_SLOT;
     }
     Map map = first_word.ToMap();
     SlotCallbackResult result =
         EvacuateObjectDefault(map, slot, first, first.SizeFromMap(map),
                               Map::ObjectFieldsFrom(map.visitor_id()));
-    object.map_slot().Release_Store(
-        MapWord::FromForwardingAddress(slot.ToHeapObject()).ToMap());
+    object.synchronized_set_map_word(
+        MapWord::FromForwardingAddress(slot.ToHeapObject()));
     return result;
   }
   DCHECK_EQ(ObjectFields::kMaybePointers,

src/objects/heap-object.h

@@ -9,6 +9,7 @@
 #include "src/roots/roots.h"
 
 #include "src/objects/objects.h"
+#include "src/objects/tagged-field.h"
 
 // Has to be the last include (doesn't have include guards):
 #include "src/objects/object-macros.h"
@@ -45,6 +46,10 @@ class HeapObject : public Object {
   // Set the map using release store
   inline void synchronized_set_map(Map value);
   inline void synchronized_set_map_word(MapWord map_word);
+  // Compare-and-swaps map word using release store, returns true if the map
+  // word was actually swapped.
+  inline bool synchronized_compare_and_swap_map_word(MapWord old_map_word,
+                                                     MapWord new_map_word);
 
   // Initialize the map immediately after the object is allocated.
   // Do not use this outside Heap.
@@ -191,6 +196,8 @@ class HeapObject : public Object {
 
   STATIC_ASSERT(kMapOffset == Internals::kHeapObjectMapOffset);
 
+  using MapField = TaggedField<MapWord, HeapObject::kMapOffset>;
+
   inline Address GetFieldAddress(int field_offset) const;
 
  protected:

src/objects/maybe-object.h

@@ -30,6 +30,10 @@ class MaybeObject : public TaggedImpl<HeapObjectReferenceType::WEAK, Address> {
 #ifdef VERIFY_HEAP
   static void VerifyMaybeObjectPointer(Isolate* isolate, MaybeObject p);
 #endif
+
+ private:
+  template <typename TFieldType, int kFieldOffset>
+  friend class TaggedField;
 };
 
 // A HeapObjectReference is either a strong reference to a HeapObject, a weak

src/objects/object-macros.h

@@ -18,11 +18,14 @@
 
 // Since this changes visibility, it should always be last in a class
 // definition.
-#define OBJECT_CONSTRUCTORS(Type, ...)            \
- public:                                          \
-  constexpr Type() : __VA_ARGS__() {}             \
-                                                  \
- protected:                                       \
+#define OBJECT_CONSTRUCTORS(Type, ...)             \
+ public:                                           \
+  constexpr Type() : __VA_ARGS__() {}              \
+                                                   \
+ protected:                                        \
+  template <typename TFieldType, int kFieldOffset> \
+  friend class TaggedField;                        \
+                                                   \
   explicit inline Type(Address ptr)
 
 #define OBJECT_CONSTRUCTORS_IMPL(Type, Super) \
@@ -412,12 +415,15 @@
     set(IndexForEntry(i) + k##name##Offset, value);             \
   }
 
-#define TQ_OBJECT_CONSTRUCTORS(Type) \
- public:                             \
-  constexpr Type() = default;        \
-                                     \
- protected:                          \
-  inline explicit Type(Address ptr); \
+#define TQ_OBJECT_CONSTRUCTORS(Type)               \
+ public:                                           \
+  constexpr Type() = default;                      \
+                                                   \
+ protected:                                        \
+  template <typename TFieldType, int kFieldOffset> \
+  friend class TaggedField;                        \
+                                                   \
+  inline explicit Type(Address ptr);               \
   friend class TorqueGenerated##Type<Type, Super>;
 
 #define TQ_OBJECT_CONSTRUCTORS_IMPL(Type) \

src/objects/objects-inl.h

@@ -38,6 +38,7 @@
 #include "src/objects/shared-function-info.h"
 #include "src/objects/slots-inl.h"
 #include "src/objects/smi-inl.h"
+#include "src/objects/tagged-field-inl.h"
 #include "src/objects/tagged-impl-inl.h"
 #include "src/objects/templates.h"
 #include "src/sanitizer/tsan.h"
@@ -709,23 +710,28 @@ void HeapObject::set_map_after_allocation(Map value, WriteBarrierMode mode) {
 }
 
 MapWordSlot HeapObject::map_slot() const {
-  return MapWordSlot(FIELD_ADDR(*this, kMapOffset));
+  return MapWordSlot(MapField::address(*this));
 }
 
-MapWord HeapObject::map_word() const {
-  return MapWord(map_slot().Relaxed_Load().ptr());
-}
+MapWord HeapObject::map_word() const { return MapField::Relaxed_Load(*this); }
 
 void HeapObject::set_map_word(MapWord map_word) {
-  map_slot().Relaxed_Store(Object(map_word.value_));
+  MapField::Relaxed_Store(*this, map_word);
 }
 
 MapWord HeapObject::synchronized_map_word() const {
-  return MapWord(map_slot().Acquire_Load().ptr());
+  return MapField::Acquire_Load(*this);
 }
 
 void HeapObject::synchronized_set_map_word(MapWord map_word) {
-  map_slot().Release_Store(Object(map_word.value_));
+  MapField::Release_Store(*this, map_word);
+}
+
+bool HeapObject::synchronized_compare_and_swap_map_word(MapWord old_map_word,
+                                                        MapWord new_map_word) {
+  Tagged_t result =
+      MapField::Release_CompareAndSwap(*this, old_map_word, new_map_word);
+  return result == static_cast<Tagged_t>(old_map_word.ptr());
 }
 
 int HeapObject::Size() const { return SizeFromMap(map()); }

src/objects/objects.h

@@ -743,13 +743,13 @@ class MapWord {
   // View this map word as a forwarding address.
   inline HeapObject ToForwardingAddress();
 
-  static inline MapWord FromRawValue(uintptr_t value) { return MapWord(value); }
-
-  inline uintptr_t ToRawValue() { return value_; }
+  inline Address ptr() { return value_; }
 
  private:
   // HeapObject calls the private constructor and directly reads the value.
   friend class HeapObject;
+  template <typename TFieldType, int kFieldOffset>
+  friend class TaggedField;
 
   explicit MapWord(Address value) : value_(value) {}
 

src/objects/tagged-field-inl.h

@@ -0,0 +1,131 @@
+// Copyright 2019 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.
+
+#ifndef V8_OBJECTS_TAGGED_FIELD_INL_H_
+#define V8_OBJECTS_TAGGED_FIELD_INL_H_
+
+#include "src/objects/tagged-field.h"
+
+#include "src/common/ptr-compr-inl.h"
+
+namespace v8 {
+namespace internal {
+
+// static
+template <typename T, int kFieldOffset>
+Address TaggedField<T, kFieldOffset>::address(HeapObject host) {
+  return host.address() + kFieldOffset;
+}
+
+// static
+template <typename T, int kFieldOffset>
+Tagged_t* TaggedField<T, kFieldOffset>::location(HeapObject host) {
+  return reinterpret_cast<Tagged_t*>(address(host));
+}
+
+// static
+template <typename T, int kFieldOffset>
+template <typename TOnHeapAddress>
+Address TaggedField<T, kFieldOffset>::tagged_to_full(
+    TOnHeapAddress on_heap_addr, Tagged_t tagged_value) {
+#ifdef V8_COMPRESS_POINTERS
+  if (kIsSmi) {
+    return DecompressTaggedSigned(tagged_value);
+  } else if (kIsHeapObject) {
+    return DecompressTaggedPointer(on_heap_addr, tagged_value);
+  } else {
+    return DecompressTaggedAny(on_heap_addr, tagged_value);
+  }
+#else
+  return tagged_value;
+#endif
+}
+
+// static
+template <typename T, int kFieldOffset>
+Tagged_t TaggedField<T, kFieldOffset>::full_to_tagged(Address value) {
+#ifdef V8_COMPRESS_POINTERS
+  return CompressTagged(value);
+#else
+  return value;
+#endif
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::load(HeapObject host) {
+  Tagged_t value = *location(host);
+  return T(tagged_to_full(host.ptr(), value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::load(Isolate* isolate, HeapObject host) {
+  Tagged_t value = *location(host);
+  return T(tagged_to_full(isolate, value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+void TaggedField<T, kFieldOffset>::store(HeapObject host, T value) {
+  *location(host) = full_to_tagged(value.ptr());
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::Relaxed_Load(HeapObject host) {
+  AtomicTagged_t value = AsAtomicTagged::Relaxed_Load(location(host));
+  return T(tagged_to_full(host.ptr(), value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::Relaxed_Load(Isolate* isolate,
+                                             HeapObject host) {
+  AtomicTagged_t value = AsAtomicTagged::Relaxed_Load(location(host));
+  return T(tagged_to_full(isolate, value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+void TaggedField<T, kFieldOffset>::Relaxed_Store(HeapObject host, T value) {
+  AsAtomicTagged::Relaxed_Store(location(host), full_to_tagged(value.ptr()));
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::Acquire_Load(HeapObject host) {
+  AtomicTagged_t value = AsAtomicTagged::Acquire_Load(location(host));
+  return T(tagged_to_full(host.ptr(), value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+T TaggedField<T, kFieldOffset>::Acquire_Load(Isolate* isolate,
+                                             HeapObject host) {
+  AtomicTagged_t value = AsAtomicTagged::Acquire_Load(location(host));
+  return T(tagged_to_full(isolate, value));
+}
+
+// static
+template <typename T, int kFieldOffset>
+void TaggedField<T, kFieldOffset>::Release_Store(HeapObject host, T value) {
+  AsAtomicTagged::Release_Store(location(host), full_to_tagged(value.ptr()));
+}
+
+// static
+template <typename T, int kFieldOffset>
+Tagged_t TaggedField<T, kFieldOffset>::Release_CompareAndSwap(HeapObject host,
+                                                              T old, T value) {
+  Tagged_t old_value = full_to_tagged(old.ptr());
+  Tagged_t new_value = full_to_tagged(value.ptr());
+  Tagged_t result = AsAtomicTagged::Release_CompareAndSwap(
+      location(host), old_value, new_value);
+  return result;
+}
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_OBJECTS_TAGGED_FIELD_INL_H_

src/objects/tagged-field.h

@@ -0,0 +1,71 @@
+// Copyright 2019 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.
+
+#ifndef V8_OBJECTS_TAGGED_FIELD_H_
+#define V8_OBJECTS_TAGGED_FIELD_H_
+
+#include "src/common/globals.h"
+
+#include "src/objects/objects.h"
+#include "src/objects/tagged-value.h"
+
+namespace v8 {
+namespace internal {
+
+// This helper static class represents a tagged field of type T at offset
+// kFieldOffset inside some host HeapObject.
+// For full-pointer mode this type adds no overhead but when pointer
+// compression is enabled such class allows us to use proper decompression
+// function depending on the field type.
+template <typename T, int kFieldOffset>
+class TaggedField : public AllStatic {
+ public:
+  static_assert(std::is_base_of<Object, T>::value ||
+                    std::is_same<MapWord, T>::value ||
+                    std::is_same<MaybeObject, T>::value,
+                "T must be strong or weak tagged type or MapWord");
+
+  // True for Smi fields.
+  static constexpr bool kIsSmi = std::is_base_of<Smi, T>::value;
+
+  // True for HeapObject and MapWord fields. The latter may look like a Smi
+  // if it contains forwarding pointer but still requires tagged pointer
+  // decompression.
+  static constexpr bool kIsHeapObject =
+      std::is_base_of<HeapObject, T>::value || std::is_same<MapWord, T>::value;
+
+  static inline Address address(HeapObject host);
+
+  static inline T load(HeapObject host);
+  static inline T load(Isolate* isolate, HeapObject host);
+
+  static inline void store(HeapObject host, T value);
+
+  static inline T Relaxed_Load(HeapObject host);
+  static inline T Relaxed_Load(Isolate* isolate, HeapObject host);
+
+  static inline void Relaxed_Store(HeapObject host, T value);
+
+  static inline T Acquire_Load(HeapObject host);
+  static inline T Acquire_Load(Isolate* isolate, HeapObject host);
+
+  static inline void Release_Store(HeapObject host, T value);
+
+  static inline Tagged_t Release_CompareAndSwap(HeapObject host, T old,
+                                                T value);
+
+ private:
+  static inline Tagged_t* location(HeapObject host);
+
+  template <typename TOnHeapAddress>
+  static inline Address tagged_to_full(TOnHeapAddress on_heap_addr,
+                                       Tagged_t tagged_value);
+
+  static inline Tagged_t full_to_tagged(Address value);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_OBJECTS_TAGGED_FIELD_H_