Line data    Source code

       1             : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
       2             :  * vim: set ts=8 sts=4 et sw=4 tw=99:
       3             :  * This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : #ifndef jit_PcScriptCache_h
       8             : #define jit_PcScriptCache_h
       9             : 
      10             : // Defines a fixed-size hash table solely for the purpose of caching jit::GetPcScript().
      11             : // One cache is attached to each JSRuntime; it functions as if cleared on GC.
      12             : 
      13             : struct JSRuntime;
      14             : 
      15             : namespace js {
      16             : namespace jit {
      17             : 
      18             : struct PcScriptCacheEntry
      19             : {
      20             :     uint8_t* returnAddress; // Key into the hash table.
      21             :     jsbytecode* pc;         // Cached PC.
      22             :     JSScript* script;       // Cached script.
      23             : };
      24             : 
      25             : struct PcScriptCache
      26             : {
      27             :     static const uint32_t Length = 73;
      28             : 
      29             :     // GC number at the time the cache was filled or created.
      30             :     // Storing and checking against this number allows us to not bother
      31             :     // clearing this cache on every GC -- only when actually necessary.
      32             :     uint64_t gcNumber;
      33             : 
      34             :     // List of cache entries.
      35             :     mozilla::Array<PcScriptCacheEntry, Length> entries;
      36             : 
      37          23 :     void clear(uint64_t gcNumber) {
      38        1702 :         for (uint32_t i = 0; i < Length; i++)
      39        1679 :             entries[i].returnAddress = nullptr;
      40          23 :         this->gcNumber = gcNumber;
      41          23 :     }
      42             : 
      43             :     // Get a value from the cache. May perform lazy allocation.
      44        4072 :     MOZ_MUST_USE bool get(JSRuntime* rt, uint32_t hash, uint8_t* addr,
      45             :                           JSScript** scriptRes, jsbytecode** pcRes)
      46             :     {
      47             :         // If a GC occurred, lazily clear the cache now.
      48        4072 :         if (gcNumber != rt->gc.gcNumber()) {
      49          19 :             clear(rt->gc.gcNumber());
      50          19 :             return false;
      51             :         }
      52             : 
      53        4053 :         if (entries[hash].returnAddress != addr)
      54        1314 :             return false;
      55             : 
      56        2739 :         *scriptRes = entries[hash].script;
      57        2739 :         if (pcRes)
      58         706 :             *pcRes = entries[hash].pc;
      59             : 
      60        2739 :         return true;
      61             :     }
      62             : 
      63        1333 :     void add(uint32_t hash, uint8_t* addr, jsbytecode* pc, JSScript* script) {
      64        1333 :         MOZ_ASSERT(addr);
      65        1333 :         MOZ_ASSERT(pc);
      66        1333 :         MOZ_ASSERT(script);
      67        1333 :         entries[hash].returnAddress = addr;
      68        1333 :         entries[hash].pc = pc;
      69        1333 :         entries[hash].script = script;
      70        1333 :     }
      71             : 
      72        4072 :     static uint32_t Hash(uint8_t* addr) {
      73        4072 :         uint32_t key = (uint32_t)((uintptr_t)addr);
      74        4072 :         return ((key >> 3) * 2654435761u) % Length;
      75             :     }
      76             : };
      77             : 
      78             : } // namespace jit
      79             : } // namespace js
      80             : 
      81             : #endif /* jit_PcScriptCache_h */