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// Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#include "vm/allocation.h"
#include "vm/raw_object.h"
namespace dart {
class Array;
// Objects that are a source in a become are tranformed into forwarding
// corpses pointing to the corresponding target. Forwarding corpses have the
// same heap sizes as the source object to ensure the heap remains walkable.
// If the heap sizes is small enough to be encoded in the size field of the
// header, a forwarding corpse consists only of a header and the target pointer.
// If the heap size is too big to be encoded in the header's size field, the
// word after the target pointer contains the size. This is the same
// representation as a FreeListElement.
class ForwardingCorpse {
RawObject* target() const { return target_; }
void set_target(RawObject* target) { target_ = target; }
intptr_t Size() {
intptr_t size = RawObject::SizeTag::decode(tags_);
if (size != 0) return size;
return *SizeAddress();
static ForwardingCorpse* AsForwarder(uword addr, intptr_t size);
static void InitOnce();
// Used to allocate class for forwarding corpses in Object::InitOnce.
class FakeInstance {
FakeInstance() {}
static cpp_vtable vtable() { return 0; }
static intptr_t InstanceSize() { return 0; }
static intptr_t NextFieldOffset() { return -kWordSize; }
static const ClassId kClassId = kForwardingCorpse;
static bool IsInstance() { return true; }
// This layout mirrors the layout of RawObject.
uint32_t tags_;
uint32_t hash_;
RawObject* target_;
// Returns the address of the embedded size.
intptr_t* SizeAddress() const {
uword addr = reinterpret_cast<uword>(&target_) + kWordSize;
return reinterpret_cast<intptr_t*>(addr);
// ForwardingCorpses cannot be allocated. Instead references to them are
// created using the AsForwarder factory method.
// TODO(johnmccutchan): Refactor this class so that it is not all static and
// provides utility methods for building the mapping of before and after.
class Become : public AllStatic {
// Smalltalk's one-way bulk become (Array>>#elementsForwardIdentityTo:).
// Redirects all pointers to elements of 'before' to the corresponding element
// in 'after'. Every element in 'before' is guaranteed to be not reachable.
// Useful for atomically applying behavior and schema changes.
static void ElementsForwardIdentity(const Array& before, const Array& after);
// Update any references pointing to forwarding objects to point the
// forwarding objects' targets. Used by the implementation of become and the
// simplistic compactor.
static void FollowForwardingPointers(Thread* thread);
// Convert and instance object into a dummy object,
// making the instance independent of its class.
// (used for morphic instances during reload).
static void MakeDummyObject(const Instance& instance);
static void CrashDump(RawObject* before_obj, RawObject* after_obj);
} // namespace dart