Line data    Source code

       1             : // Copyright 2012 the V8 project authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file.
       4             : 
       5             : #ifndef V8_IC_STUB_CACHE_H_
       6             : #define V8_IC_STUB_CACHE_H_
       7             : 
       8             : #include "src/objects/name.h"
       9             : 
      10             : namespace v8 {
      11             : namespace internal {
      12             : 
      13             : // The stub cache is used for megamorphic property accesses.
      14             : // It maps (map, name, type) to property access handlers. The cache does not
      15             : // need explicit invalidation when a prototype chain is modified, since the
      16             : // handlers verify the chain.
      17             : 
      18             : 
      19             : class SCTableReference {
      20             :  public:
      21         570 :   Address address() const { return address_; }
      22             : 
      23             :  private:
      24             :   explicit SCTableReference(Address address) : address_(address) {}
      25             : 
      26             :   Address address_;
      27             : 
      28             :   friend class StubCache;
      29             : };
      30             : 
      31             : 
      32             : class StubCache {
      33             :  public:
      34             :   struct Entry {
      35             :     // The values here have plain Address types because they are read
      36             :     // directly from generated code. As a nice side effect, this keeps
      37             :     // #includes lightweight.
      38             :     Address key;
      39             :     // {value} is a tagged heap object reference (weak or strong), equivalent
      40             :     // to a MaybeObject's payload.
      41             :     Address value;
      42             :     // {map} is a tagged Map pointer, or nullptr.
      43             :     Address map;
      44             :   };
      45             : 
      46             :   void Initialize();
      47             :   // Access cache for entry hash(name, map).
      48             :   void Set(Name name, Map map, MaybeObject handler);
      49             :   MaybeObject Get(Name name, Map map);
      50             :   // Clear the lookup table (@ mark compact collection).
      51             :   void Clear();
      52             : 
      53             :   enum Table { kPrimary, kSecondary };
      54             : 
      55             :   SCTableReference key_reference(StubCache::Table table) {
      56             :     return SCTableReference(
      57      252102 :         reinterpret_cast<Address>(&first_entry(table)->key));
      58             :   }
      59             : 
      60             :   SCTableReference map_reference(StubCache::Table table) {
      61             :     return SCTableReference(
      62      251532 :         reinterpret_cast<Address>(&first_entry(table)->map));
      63             :   }
      64             : 
      65             :   SCTableReference value_reference(StubCache::Table table) {
      66             :     return SCTableReference(
      67      251532 :         reinterpret_cast<Address>(&first_entry(table)->value));
      68             :   }
      69             : 
      70      755166 :   StubCache::Entry* first_entry(StubCache::Table table) {
      71      755166 :     switch (table) {
      72             :       case StubCache::kPrimary:
      73      377583 :         return StubCache::primary_;
      74             :       case StubCache::kSecondary:
      75      377583 :         return StubCache::secondary_;
      76             :     }
      77           0 :     UNREACHABLE();
      78             :   }
      79             : 
      80             :   Isolate* isolate() { return isolate_; }
      81             : 
      82             :   // Setting the entry size such that the index is shifted by Name::kHashShift
      83             :   // is convenient; shifting down the length field (to extract the hash code)
      84             :   // automatically discards the hash bit field.
      85             :   static const int kCacheIndexShift = Name::kHashShift;
      86             : 
      87             :   static const int kPrimaryTableBits = 11;
      88             :   static const int kPrimaryTableSize = (1 << kPrimaryTableBits);
      89             :   static const int kSecondaryTableBits = 9;
      90             :   static const int kSecondaryTableSize = (1 << kSecondaryTableBits);
      91             : 
      92             :   // Some magic number used in the secondary hash computation.
      93             :   static const int kSecondaryMagic = 0xb16ca6e5;
      94             : 
      95             :   static int PrimaryOffsetForTesting(Name name, Map map);
      96             :   static int SecondaryOffsetForTesting(Name name, int seed);
      97             : 
      98             :   // The constructor is made public only for the purposes of testing.
      99             :   explicit StubCache(Isolate* isolate);
     100             : 
     101             :  private:
     102             :   // The stub cache has a primary and secondary level.  The two levels have
     103             :   // different hashing algorithms in order to avoid simultaneous collisions
     104             :   // in both caches.  Unlike a probing strategy (quadratic or otherwise) the
     105             :   // update strategy on updates is fairly clear and simple:  Any existing entry
     106             :   // in the primary cache is moved to the secondary cache, and secondary cache
     107             :   // entries are overwritten.
     108             : 
     109             :   // Hash algorithm for the primary table.  This algorithm is replicated in
     110             :   // assembler for every architecture.  Returns an index into the table that
     111             :   // is scaled by 1 << kCacheIndexShift.
     112             :   static int PrimaryOffset(Name name, Map map);
     113             : 
     114             :   // Hash algorithm for the secondary table.  This algorithm is replicated in
     115             :   // assembler for every architecture.  Returns an index into the table that
     116             :   // is scaled by 1 << kCacheIndexShift.
     117             :   static int SecondaryOffset(Name name, int seed);
     118             : 
     119             :   // Compute the entry for a given offset in exactly the same way as
     120             :   // we do in generated code.  We generate an hash code that already
     121             :   // ends in Name::kHashShift 0s.  Then we multiply it so it is a multiple
     122             :   // of sizeof(Entry).  This makes it easier to avoid making mistakes
     123             :   // in the hashed offset computations.
     124             :   static Entry* entry(Entry* table, int offset) {
     125             :     const int multiplier = sizeof(*table) >> Name::kHashShift;
     126     1227142 :     return reinterpret_cast<Entry*>(reinterpret_cast<Address>(table) +
     127     2454284 :                                     offset * multiplier);
     128             :   }
     129             : 
     130             :  private:
     131             :   Entry primary_[kPrimaryTableSize];
     132             :   Entry secondary_[kSecondaryTableSize];
     133             :   Isolate* isolate_;
     134             : 
     135             :   friend class Isolate;
     136             :   friend class SCTableReference;
     137             : 
     138             :   DISALLOW_COPY_AND_ASSIGN(StubCache);
     139             : };
     140             : }  // namespace internal
     141             : }  // namespace v8
     142             : 
     143             : #endif  // V8_IC_STUB_CACHE_H_