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Diffstat (limited to '')
-rw-r--r-- | js/src/jit/PcScriptCache.h | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/js/src/jit/PcScriptCache.h b/js/src/jit/PcScriptCache.h new file mode 100644 index 0000000000..c83c479c85 --- /dev/null +++ b/js/src/jit/PcScriptCache.h @@ -0,0 +1,88 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#ifndef jit_PcScriptCache_h +#define jit_PcScriptCache_h + +#include "mozilla/Array.h" +#include "js/TypeDecls.h" +#include "vm/Runtime.h" + +// Defines a fixed-size hash table solely for the purpose of caching +// jit::GetPcScript(). One cache is attached to each JSRuntime; it functions as +// if cleared on GC. + +namespace js { +namespace jit { + +struct PcScriptCacheEntry { + uint8_t* returnAddress; // Key into the hash table. + jsbytecode* pc; // Cached PC. + JSScript* script; // Cached script. +}; + +struct PcScriptCache { + private: + static const uint32_t Length = 73; + + // GC number at the time the cache was filled or created. + // Storing and checking against this number allows us to not bother + // clearing this cache on every GC -- only when actually necessary. + uint64_t gcNumber; + + // List of cache entries. + mozilla::Array<PcScriptCacheEntry, Length> entries; + + public: + explicit PcScriptCache(uint64_t gcNumber) { clear(gcNumber); } + + void clear(uint64_t gcNumber) { + for (uint32_t i = 0; i < Length; i++) { + entries[i].returnAddress = nullptr; + } + this->gcNumber = gcNumber; + } + + // Get a value from the cache. May perform lazy allocation. + [[nodiscard]] bool get(JSRuntime* rt, uint32_t hash, uint8_t* addr, + JSScript** scriptRes, jsbytecode** pcRes) { + // If a GC occurred, lazily clear the cache now. + if (gcNumber != rt->gc.gcNumber()) { + clear(rt->gc.gcNumber()); + return false; + } + + if (entries[hash].returnAddress != addr) { + return false; + } + + *scriptRes = entries[hash].script; + if (pcRes) { + *pcRes = entries[hash].pc; + } + + return true; + } + + void add(uint32_t hash, uint8_t* addr, jsbytecode* pc, JSScript* script) { + MOZ_ASSERT(addr); + MOZ_ASSERT(pc); + MOZ_ASSERT(script); + entries[hash].returnAddress = addr; + entries[hash].pc = pc; + entries[hash].script = script; + } + + static uint32_t Hash(uint8_t* addr) { + uint32_t key = (uint32_t)((uintptr_t)addr); + return ((key >> 3) * 2654435761u) % Length; + } +}; + +} // namespace jit +} // namespace js + +#endif /* jit_PcScriptCache_h */ |