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/* -*- 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_JitHints_h
#define jit_JitHints_h
#include "mozilla/BloomFilter.h"
#include "vm/JSScript.h"
namespace js::jit {
/*
* The JitHintsMap implements a BitBloomFilter to track whether or not a script,
* identified by filename+sourceStart, has been baseline compiled before in the
* same process. This can occur frequently during navigations.
*
* The bloom filter allows us to have very efficient storage and lookup costs,
* at the expense of occasional false positives. The number of entries added
* to the bloom filter is monitored in order to try and keep the false
* positivity rate below 1%. If the entry count exceeds MaxEntries_, which
* indicates the false positivity rate may exceed 1.5%, then the filter is
* completely cleared to reset the cache.
*/
class JitHintsMap {
// ScriptKey is a hash on the filename+sourceStart.
using ScriptKey = HashNumber;
static constexpr uint32_t CacheSize_ = 16;
mozilla::BitBloomFilter<CacheSize_, ScriptKey> map_;
/*
* MaxEntries_ is the approximate entry count for which the
* false positivity rate will exceed p=0.015 using k=2 and m=2**CacheSize.
* Formula is as follows:
* MaxEntries_ = floor(m / (-k / ln(1-exp(ln(p) / k))))
*/
static constexpr uint32_t MaxEntries_ = 4281;
static_assert(CacheSize_ == 16 && MaxEntries_ == 4281,
"MaxEntries should be recalculated for given CacheSize.");
uint32_t entryCount_ = 0;
ScriptKey getScriptKey(JSScript* script) const;
void incrementEntryCount();
public:
void setEagerBaselineHint(JSScript* script);
bool mightHaveEagerBaselineHint(JSScript* script) const;
};
} // namespace js::jit
#endif /* jit_JitHints_h */
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