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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* 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
// 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.
struct JSRuntime;
namespace js {
namespace jit {
struct PcScriptCacheEntry
{
uint8_t* returnAddress; // Key into the hash table.
jsbytecode* pc; // Cached PC.
JSScript* script; // Cached script.
};
struct PcScriptCache
{
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;
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 */
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