michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set ts=8 sts=4 et sw=4 tw=99:
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef jit_PcScriptCache_h
michael@0: #define jit_PcScriptCache_h
michael@0: 
michael@0: // Defines a fixed-size hash table solely for the purpose of caching jit::GetPcScript().
michael@0: // One cache is attached to each JSRuntime; it functions as if cleared on GC.
michael@0: 
michael@0: struct JSRuntime;
michael@0: 
michael@0: namespace js {
michael@0: namespace jit {
michael@0: 
michael@0: struct PcScriptCacheEntry
michael@0: {
michael@0:     uint8_t *returnAddress; // Key into the hash table.
michael@0:     jsbytecode *pc;         // Cached PC.
michael@0:     JSScript *script;       // Cached script.
michael@0: };
michael@0: 
michael@0: struct PcScriptCache
michael@0: {
michael@0:     static const uint32_t Length = 73;
michael@0: 
michael@0:     // GC number at the time the cache was filled or created.
michael@0:     // Storing and checking against this number allows us to not bother
michael@0:     // clearing this cache on every GC -- only when actually necessary.
michael@0:     uint64_t gcNumber;
michael@0: 
michael@0:     // List of cache entries.
michael@0:     mozilla::Array<PcScriptCacheEntry, Length> entries;
michael@0: 
michael@0:     void clear(uint64_t gcNumber) {
michael@0:         for (uint32_t i = 0; i < Length; i++)
michael@0:             entries[i].returnAddress = nullptr;
michael@0:         this->gcNumber = gcNumber;
michael@0:     }
michael@0: 
michael@0:     // Get a value from the cache. May perform lazy allocation.
michael@0:     bool get(JSRuntime *rt, uint32_t hash, uint8_t *addr,
michael@0:              JSScript **scriptRes, jsbytecode **pcRes)
michael@0:     {
michael@0:         // If a GC occurred, lazily clear the cache now.
michael@0:         if (gcNumber != rt->gcNumber) {
michael@0:             clear(rt->gcNumber);
michael@0:             return false;
michael@0:         }
michael@0: 
michael@0:         if (entries[hash].returnAddress != addr)
michael@0:             return false;
michael@0: 
michael@0:         *scriptRes = entries[hash].script;
michael@0:         if (pcRes)
michael@0:             *pcRes = entries[hash].pc;
michael@0: 
michael@0:         return true;
michael@0:     }
michael@0: 
michael@0:     void add(uint32_t hash, uint8_t *addr, jsbytecode *pc, JSScript *script) {
michael@0:         entries[hash].returnAddress = addr;
michael@0:         entries[hash].pc = pc;
michael@0:         entries[hash].script = script;
michael@0:     }
michael@0: 
michael@0:     static uint32_t Hash(uint8_t *addr) {
michael@0:         uint32_t key = (uint32_t)((uintptr_t)addr);
michael@0:         return ((key >> 3) * 2654435761u) % Length;
michael@0:     }
michael@0: };
michael@0: 
michael@0: } // namespace jit
michael@0: } // namespace js
michael@0: 
michael@0: #endif /* jit_PcScriptCache_h */