1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/js/src/jit/PcScriptCache.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,78 @@
1.4 +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
1.5 + * vim: set ts=8 sts=4 et sw=4 tw=99:
1.6 + * This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +#ifndef jit_PcScriptCache_h
1.11 +#define jit_PcScriptCache_h
1.12 +
1.13 +// Defines a fixed-size hash table solely for the purpose of caching jit::GetPcScript().
1.14 +// One cache is attached to each JSRuntime; it functions as if cleared on GC.
1.15 +
1.16 +struct JSRuntime;
1.17 +
1.18 +namespace js {
1.19 +namespace jit {
1.20 +
1.21 +struct PcScriptCacheEntry
1.22 +{
1.23 + uint8_t *returnAddress; // Key into the hash table.
1.24 + jsbytecode *pc; // Cached PC.
1.25 + JSScript *script; // Cached script.
1.26 +};
1.27 +
1.28 +struct PcScriptCache
1.29 +{
1.30 + static const uint32_t Length = 73;
1.31 +
1.32 + // GC number at the time the cache was filled or created.
1.33 + // Storing and checking against this number allows us to not bother
1.34 + // clearing this cache on every GC -- only when actually necessary.
1.35 + uint64_t gcNumber;
1.36 +
1.37 + // List of cache entries.
1.38 + mozilla::Array<PcScriptCacheEntry, Length> entries;
1.39 +
1.40 + void clear(uint64_t gcNumber) {
1.41 + for (uint32_t i = 0; i < Length; i++)
1.42 + entries[i].returnAddress = nullptr;
1.43 + this->gcNumber = gcNumber;
1.44 + }
1.45 +
1.46 + // Get a value from the cache. May perform lazy allocation.
1.47 + bool get(JSRuntime *rt, uint32_t hash, uint8_t *addr,
1.48 + JSScript **scriptRes, jsbytecode **pcRes)
1.49 + {
1.50 + // If a GC occurred, lazily clear the cache now.
1.51 + if (gcNumber != rt->gcNumber) {
1.52 + clear(rt->gcNumber);
1.53 + return false;
1.54 + }
1.55 +
1.56 + if (entries[hash].returnAddress != addr)
1.57 + return false;
1.58 +
1.59 + *scriptRes = entries[hash].script;
1.60 + if (pcRes)
1.61 + *pcRes = entries[hash].pc;
1.62 +
1.63 + return true;
1.64 + }
1.65 +
1.66 + void add(uint32_t hash, uint8_t *addr, jsbytecode *pc, JSScript *script) {
1.67 + entries[hash].returnAddress = addr;
1.68 + entries[hash].pc = pc;
1.69 + entries[hash].script = script;
1.70 + }
1.71 +
1.72 + static uint32_t Hash(uint8_t *addr) {
1.73 + uint32_t key = (uint32_t)((uintptr_t)addr);
1.74 + return ((key >> 3) * 2654435761u) % Length;
1.75 + }
1.76 +};
1.77 +
1.78 +} // namespace jit
1.79 +} // namespace js
1.80 +
1.81 +#endif /* jit_PcScriptCache_h */
