// Copyright 2012 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_IC_STUB_CACHE_H_
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#define V8_IC_STUB_CACHE_H_
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#include "src/macro-assembler.h"
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#include "src/objects/name.h"
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namespace v8 {
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namespace internal {
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// The stub cache is used for megamorphic property accesses.
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// It maps (map, name, type) to property access handlers. The cache does not
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// need explicit invalidation when a prototype chain is modified, since the
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// handlers verify the chain.
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class SCTableReference {
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public:
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Address address() const { return address_; }
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private:
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explicit SCTableReference(Address address) : address_(address) {}
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Address address_;
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friend class StubCache;
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};
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class StubCache {
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public:
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struct Entry {
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Name* key;
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MaybeObject* value;
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Map* map;
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};
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void Initialize();
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// Access cache for entry hash(name, map).
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MaybeObject* Set(Name* name, Map* map, MaybeObject* handler);
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MaybeObject* Get(Name* name, Map* map);
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// Clear the lookup table (@ mark compact collection).
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void Clear();
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enum Table { kPrimary, kSecondary };
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SCTableReference key_reference(StubCache::Table table) {
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return SCTableReference(
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reinterpret_cast<Address>(&first_entry(table)->key));
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}
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SCTableReference map_reference(StubCache::Table table) {
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return SCTableReference(
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reinterpret_cast<Address>(&first_entry(table)->map));
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}
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SCTableReference value_reference(StubCache::Table table) {
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return SCTableReference(
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reinterpret_cast<Address>(&first_entry(table)->value));
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}
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StubCache::Entry* first_entry(StubCache::Table table) {
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switch (table) {
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case StubCache::kPrimary:
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return StubCache::primary_;
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case StubCache::kSecondary:
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return StubCache::secondary_;
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}
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UNREACHABLE();
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}
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Isolate* isolate() { return isolate_; }
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// Setting the entry size such that the index is shifted by Name::kHashShift
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// is convenient; shifting down the length field (to extract the hash code)
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// automatically discards the hash bit field.
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static const int kCacheIndexShift = Name::kHashShift;
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static const int kPrimaryTableBits = 11;
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static const int kPrimaryTableSize = (1 << kPrimaryTableBits);
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static const int kSecondaryTableBits = 9;
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static const int kSecondaryTableSize = (1 << kSecondaryTableBits);
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// Some magic number used in the secondary hash computation.
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static const int kSecondaryMagic = 0xb16ca6e5;
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static int PrimaryOffsetForTesting(Name* name, Map* map) {
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return PrimaryOffset(name, map);
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}
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static int SecondaryOffsetForTesting(Name* name, int seed) {
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return SecondaryOffset(name, seed);
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}
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// The constructor is made public only for the purposes of testing.
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explicit StubCache(Isolate* isolate);
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private:
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// The stub cache has a primary and secondary level. The two levels have
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// different hashing algorithms in order to avoid simultaneous collisions
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// in both caches. Unlike a probing strategy (quadratic or otherwise) the
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// update strategy on updates is fairly clear and simple: Any existing entry
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// in the primary cache is moved to the secondary cache, and secondary cache
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// entries are overwritten.
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// Hash algorithm for the primary table. This algorithm is replicated in
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// assembler for every architecture. Returns an index into the table that
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// is scaled by 1 << kCacheIndexShift.
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static int PrimaryOffset(Name* name, Map* map);
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// Hash algorithm for the secondary table. This algorithm is replicated in
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// assembler for every architecture. Returns an index into the table that
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// is scaled by 1 << kCacheIndexShift.
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static int SecondaryOffset(Name* name, int seed);
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// Compute the entry for a given offset in exactly the same way as
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// we do in generated code. We generate an hash code that already
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// ends in Name::kHashShift 0s. Then we multiply it so it is a multiple
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// of sizeof(Entry). This makes it easier to avoid making mistakes
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// in the hashed offset computations.
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static Entry* entry(Entry* table, int offset) {
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const int multiplier = sizeof(*table) >> Name::kHashShift;
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return reinterpret_cast<Entry*>(reinterpret_cast<Address>(table) +
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offset * multiplier);
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}
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private:
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Entry primary_[kPrimaryTableSize];
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Entry secondary_[kSecondaryTableSize];
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Isolate* isolate_;
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friend class Isolate;
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friend class SCTableReference;
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DISALLOW_COPY_AND_ASSIGN(StubCache);
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};
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} // namespace internal
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} // namespace v8
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#endif // V8_IC_STUB_CACHE_H_
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