/* -*- 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

#include "mozilla/Array.h"
#include "js/TypeDecls.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 {
  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 */
