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