Made zone segments aligned in memory and included a pointer to the zone in the header. Larger objec…

src/zone.h

 // Copyright 2012 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_ZONE_H_
 #define V8_ZONE_H_
 
 #include <limits>
 
 #include "src/base/accounting-allocator.h"
 #include "src/base/hashmap.h"
 #include "src/base/logging.h"
+#include "src/base/platform/platform.h"
 #include "src/globals.h"
 #include "src/list.h"
 #include "src/splay-tree.h"
 
 namespace v8 {
 namespace internal {
 
 // Forward declarations.
 class Segment;
 
 
 // The Zone supports very fast allocation of small chunks of
 // memory. The chunks cannot be deallocated individually, but instead
 // the Zone supports deallocating all chunks in one fast
 // operation. The Zone is used to hold temporary data structures like
 // the abstract syntax tree, which is deallocated after compilation.
 //
 // Note: There is no need to initialize the Zone; the first time an
 // allocation is attempted, a segment of memory will be requested
 // through a call to malloc().
 //
 // Note: The implementation is inherently not thread safe. Do not use
 // from multi-threaded code.
 class Zone final {
+  friend class ZoneObject;
+  friend class Segment;
+
  public:
   explicit Zone(base::AccountingAllocator* allocator);
   ~Zone();
 
   // Allocate 'size' bytes of memory in the Zone; expands the Zone by
   // allocating new segments of memory on demand using malloc().
   void* New(size_t size);
 
   template <typename T>
   T* NewArray(size_t length) {
@@ skipping 12 matching lines @@
   // Returns true if more memory has been allocated in zones than
   // the limit allows.
   bool excess_allocation() const {
     return segment_bytes_allocated_ > kExcessLimit;
   }
 
   size_t allocation_size() const { return allocation_size_; }
 
   base::AccountingAllocator* allocator() const { return allocator_; }
 
+  // Returns the zone the pointer belongs to. Only works in case the pointer
+  // actually lies within a zone segment.
+  static Zone* GetZoneFromPointer(const void* ptr);
+
  private:
   // All pointers returned from New() have this alignment.  In addition, if the
   // object being allocated has a size that is divisible by 8 then its alignment
   // will be 8. ASan requires 8-byte alignment.
 #ifdef V8_USE_ADDRESS_SANITIZER
   static const size_t kAlignment = 8;
   STATIC_ASSERT(kPointerSize <= 8);
 #else
   static const size_t kAlignment = kPointerSize;
 #endif
 
   // Never allocate segments smaller than this size in bytes.
   static const size_t kMinimumSegmentSize = 8 * KB;
 
   // Never allocate segments larger than this size in bytes.
   static const size_t kMaximumSegmentSize = 1 * MB;
 
+  static const uint8_t kSegmentAlignmentBits = 20;
+
+  // Always align new segments to this size

[jochen (gone - plz use gerrit), 2016/09/01 12:04:52]

nit. comments should be full sentences, so here it should end in a fullstop

+  static const size_t kSegmentAlignmentSize = 1 << kSegmentAlignmentBits;
+
+  static const size_t kSegmentAlignmentMask =
+      ~((1 << kSegmentAlignmentBits) - 1);
+
+  STATIC_ASSERT(kMaximumSegmentSize <= kSegmentAlignmentSize);
+
   // Never keep segments larger than this size in bytes around.
   static const size_t kMaximumKeptSegmentSize = 64 * KB;
 
   // Report zone excess when allocation exceeds this limit.
   static const size_t kExcessLimit = 256 * MB;
 
+  static Segment* GetZoneSegmentFromPointer(const void* ptr);
+
   // The number of bytes allocated in this zone so far.
   size_t allocation_size_;
 
   // The number of bytes allocated in segments.  Note that this number
   // includes memory allocated from the OS but not yet allocated from
   // the zone.
   size_t segment_bytes_allocated_;
 
-  // Expand the Zone to hold at least 'size' more bytes and allocate
-  // the bytes. Returns the address of the newly allocated chunk of
-  // memory in the Zone. Should only be called if there isn't enough
-  // room in the Zone already.
-  Address NewExpand(size_t size);
+  Address NewNormalSegment(size_t size);
 
-  // Creates a new segment, sets it size, and pushes it to the front
-  // of the segment chain. Returns the new segment.
+  Address NewLargeObjectSegment(size_t size);
+
+  size_t CalculateSegmentSize(const size_t requested);
+
+  // Creates a new segment, initializes it. Returns the new segment.
   inline Segment* NewSegment(size_t size);
 
-  // Deletes the given segment. Does not touch the segment chain.
-  inline void DeleteSegment(Segment* segment, size_t size);
-
   // The free region in the current (front) segment is represented as
   // the half-open interval [position, limit). The 'position' variable
   // is guaranteed to be aligned as dictated by kAlignment.
   Address position_;
   Address limit_;
 
   base::AccountingAllocator* allocator_;
 
   Segment* segment_head_;
 };
 
-
 // ZoneObject is an abstraction that helps define classes of objects
 // allocated in the Zone. Use it as a base class; see ast.h.
 class ZoneObject {
  public:
   // Allocate a new ZoneObject of 'size' bytes in the Zone.
   void* operator new(size_t size, Zone* zone) { return zone->New(size); }
 
+  Zone* zone() const { return Zone::GetZoneFromPointer(this); }
+
   // Ideally, the delete operator should be private instead of
   // public, but unfortunately the compiler sometimes synthesizes
   // (unused) destructors for classes derived from ZoneObject, which
   // require the operator to be visible. MSVC requires the delete
   // operator to be public.
 
   // ZoneObjects should never be deleted individually; use
   // Zone::DeleteAll() to delete all zone objects in one go.
   void operator delete(void*, size_t) { UNREACHABLE(); }
   void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
@@ skipping 30 matching lines @@
 
 // ZoneLists are growable lists with constant-time access to the
 // elements. The list itself and all its elements are allocated in the
 // Zone. ZoneLists cannot be deleted individually; you can delete all
 // objects in the Zone by calling Zone::DeleteAll().
 template <typename T>
 class ZoneList final : public List<T, ZoneAllocationPolicy> {
  public:
   // Construct a new ZoneList with the given capacity; the length is
   // always zero. The capacity must be non-negative.
+  // The lists storage will be placed in the given zone.
   ZoneList(int capacity, Zone* zone)
-      : List<T, ZoneAllocationPolicy>(capacity, ZoneAllocationPolicy(zone)) { }
+      : List<T, ZoneAllocationPolicy>(capacity, ZoneAllocationPolicy(zone)) {}
 
   void* operator new(size_t size, Zone* zone) { return zone->New(size); }
 
   // Construct a new ZoneList by copying the elements of the given ZoneList.
   ZoneList(const ZoneList<T>& other, Zone* zone)
       : List<T, ZoneAllocationPolicy>(other.length(),
                                       ZoneAllocationPolicy(zone)) {
     AddAll(other, zone);
   }
 
-  // We add some convenience wrappers so that we can pass in a Zone
-  // instead of a (less convenient) ZoneAllocationPolicy.
   void Add(const T& element, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::Add(element, ZoneAllocationPolicy(zone));
   }
+
   void AddAll(const List<T, ZoneAllocationPolicy>& other, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::AddAll(other, ZoneAllocationPolicy(zone));
   }
+
   void AddAll(const Vector<T>& other, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::AddAll(other, ZoneAllocationPolicy(zone));
   }
+
   void InsertAt(int index, const T& element, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::InsertAt(index, element,
                                             ZoneAllocationPolicy(zone));
   }
+
   Vector<T> AddBlock(T value, int count, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     return List<T, ZoneAllocationPolicy>::AddBlock(value, count,
                                                    ZoneAllocationPolicy(zone));
   }
+
   void Allocate(int length, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::Allocate(length, ZoneAllocationPolicy(zone));
   }
+
   void Initialize(int capacity, Zone* zone) {
+    DCHECK_IMPLIES(this->has_storage_zone(), this->storage_zone() == zone);
     List<T, ZoneAllocationPolicy>::Initialize(capacity,
                                               ZoneAllocationPolicy(zone));
   }
 
+  bool has_storage_zone() const { return this->capacity() > 0; }
+
+  // Returns the zone the storage is located in
+  Zone* storage_zone() const {
+    DCHECK(this->has_storage_zone());
+    // ZoneList storage lives in a zone, so this works.
+    return Zone::GetZoneFromPointer(this->data());
+  }
+
   void operator delete(void* pointer) { UNREACHABLE(); }
   void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };
 
 
 // A zone splay tree.  The config type parameter encapsulates the
 // different configurations of a concrete splay tree (see splay-tree.h).
 // The tree itself and all its elements are allocated in the Zone.
 template <typename Config>
 class ZoneSplayTree final : public SplayTree<Config, ZoneAllocationPolicy> {
@@ skipping 12 matching lines @@
   void operator delete(void* pointer) { UNREACHABLE(); }
   void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };
 
 typedef base::TemplateHashMapImpl<ZoneAllocationPolicy> ZoneHashMap;
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ZONE_H_