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// 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_STUB_CACHE_H_
#define V8_STUB_CACHE_H_
#include "src/macro-assembler.h"
#include "src/objects/name.h"
namespace v8 {
namespace internal {
// The stub cache is used for megamorphic property accesses.
// It maps (map, name, type) to property access handlers. The cache does not
// need explicit invalidation when a prototype chain is modified, since the
// handlers verify the chain.
class SCTableReference {
Address address() const { return address_; }
explicit SCTableReference(Address address) : address_(address) {}
Address address_;
friend class StubCache;
class StubCache {
struct Entry {
Name* key;
Object* value;
Map* map;
void Initialize();
// Access cache for entry hash(name, map).
Object* Set(Name* name, Map* map, Object* handler);
Object* Get(Name* name, Map* map);
// Clear the lookup table (@ mark compact collection).
void Clear();
enum Table { kPrimary, kSecondary };
SCTableReference key_reference(StubCache::Table table) {
return SCTableReference(
SCTableReference map_reference(StubCache::Table table) {
return SCTableReference(
SCTableReference value_reference(StubCache::Table table) {
return SCTableReference(
StubCache::Entry* first_entry(StubCache::Table table) {
switch (table) {
case StubCache::kPrimary:
return StubCache::primary_;
case StubCache::kSecondary:
return StubCache::secondary_;
Isolate* isolate() { return isolate_; }
// Setting the entry size such that the index is shifted by Name::kHashShift
// is convenient; shifting down the length field (to extract the hash code)
// automatically discards the hash bit field.
static const int kCacheIndexShift = Name::kHashShift;
static const int kPrimaryTableBits = 11;
static const int kPrimaryTableSize = (1 << kPrimaryTableBits);
static const int kSecondaryTableBits = 9;
static const int kSecondaryTableSize = (1 << kSecondaryTableBits);
// Some magic number used in the secondary hash computation.
static const int kSecondaryMagic = 0xb16ca6e5;
static int PrimaryOffsetForTesting(Name* name, Map* map) {
return PrimaryOffset(name, map);
static int SecondaryOffsetForTesting(Name* name, int seed) {
return SecondaryOffset(name, seed);
// The constructor is made public only for the purposes of testing.
explicit StubCache(Isolate* isolate);
// The stub cache has a primary and secondary level. The two levels have
// different hashing algorithms in order to avoid simultaneous collisions
// in both caches. Unlike a probing strategy (quadratic or otherwise) the
// update strategy on updates is fairly clear and simple: Any existing entry
// in the primary cache is moved to the secondary cache, and secondary cache
// entries are overwritten.
// Hash algorithm for the primary table. This algorithm is replicated in
// assembler for every architecture. Returns an index into the table that
// is scaled by 1 << kCacheIndexShift.
static int PrimaryOffset(Name* name, Map* map);
// Hash algorithm for the secondary table. This algorithm is replicated in
// assembler for every architecture. Returns an index into the table that
// is scaled by 1 << kCacheIndexShift.
static int SecondaryOffset(Name* name, int seed);
// Compute the entry for a given offset in exactly the same way as
// we do in generated code. We generate an hash code that already
// ends in Name::kHashShift 0s. Then we multiply it so it is a multiple
// of sizeof(Entry). This makes it easier to avoid making mistakes
// in the hashed offset computations.
static Entry* entry(Entry* table, int offset) {
const int multiplier = sizeof(*table) >> Name::kHashShift;
return reinterpret_cast<Entry*>(reinterpret_cast<Address>(table) +
offset * multiplier);
Entry primary_[kPrimaryTableSize];
Entry secondary_[kSecondaryTableSize];
Isolate* isolate_;
friend class Isolate;
friend class SCTableReference;
} // namespace internal
} // namespace v8
#endif // V8_STUB_CACHE_H_