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-rw-r--r--js/src/jit/PcScriptCache.h81
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diff --git a/js/src/jit/PcScriptCache.h b/js/src/jit/PcScriptCache.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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.
+ MOZ_MUST_USE 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 */