solidity/tools/yulPhaser/ProgramCache.h

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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
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#pragma once
#include <tools/yulPhaser/Program.h>
#include <libyul/optimiser/Metrics.h>
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#include <map>
#include <string>
namespace solidity::phaser
{
/**
* Structure used by @a ProgramCache to store intermediate programs and metadata associated
* with them.
*/
struct CacheEntry
{
Program program;
size_t roundNumber;
CacheEntry(Program _program, size_t _roundNumber):
program(std::move(_program)),
roundNumber(_roundNumber) {}
};
/**
* Stores statistics about current cache usage.
*/
struct CacheStats
{
/// Weights used to compute totalCodeSize.
/// The goal here is to get a result proportional to the amount of memory taken by the AST.
/// Each statement/expression gets 1 just for existing. We add more if it contains any extra
/// data that won't be visited separately by ASTWalker.
static yul::CodeWeights constexpr StorageWeights = {
/* expressionStatementCost = */ 1,
/* assignmentCost = */ 1,
/* variableDeclarationCost = */ 1,
/* functionDefinitionCost = */ 1,
/* ifCost = */ 1,
/* switchCost = */ 1,
/* caseCost = */ 1,
/* forLoopCost = */ 1,
/* breakCost = */ 1,
/* continueCost = */ 1,
/* leaveCost = */ 1,
/* blockCost = */ 1,
/* functionCallCost = */ 1,
/* identifierCost = */ 1,
/* literalCost = */ 1,
};
size_t hits;
size_t misses;
size_t totalCodeSize;
std::map<size_t, size_t> roundEntryCounts;
CacheStats& operator+=(CacheStats const& _other);
CacheStats operator+(CacheStats const& _other) const { return CacheStats(*this) += _other; }
bool operator==(CacheStats const& _other) const;
bool operator!=(CacheStats const& _other) const { return !(*this == _other); }
};
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/**
* Class that optimises programs one step at a time which allows it to store and later reuse the
* results of the intermediate steps.
*
* The cache keeps track of the current round number and associates newly created entries with it.
* @a startRound() must be called at the beginning of a round so that entries that are too old
* can be purged. The current strategy is to store programs corresponding to all possible prefixes
* encountered in the current and the previous rounds. Entries older than that get removed to
* conserve memory.
*
* @a gatherStats() allows getting statistics useful for determining cache effectiveness.
*
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* The current strategy does speed things up (about 4:1 hit:miss ratio observed in my limited
* experiments) but there's room for improvement. We could fit more useful programs in
* the cache by being more picky about which ones we choose.
*
* There is currently no way to purge entries without starting a new round. Since the programs
* take a lot of memory, this may lead to the cache eating up all the available RAM if sequences are
* long and programs large. A limiter based on entry count or total program size would be useful.
*/
class ProgramCache
{
public:
explicit ProgramCache(Program _program):
m_program(std::move(_program)) {}
Program optimiseProgram(
std::string const& _abbreviatedOptimisationSteps,
size_t _repetitionCount = 1
);
void startRound(size_t _nextRoundNumber);
void clear();
size_t size() const { return m_entries.size(); }
Program const* find(std::string const& _abbreviatedOptimisationSteps) const;
bool contains(std::string const& _abbreviatedOptimisationSteps) const { return find(_abbreviatedOptimisationSteps) != nullptr; }
CacheStats gatherStats() const;
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std::map<std::string, CacheEntry> const& entries() const { return m_entries; };
Program const& program() const { return m_program; }
size_t currentRound() const { return m_currentRound; }
private:
size_t calculateTotalCachedCodeSize() const;
std::map<size_t, size_t> countRoundEntries() const;
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// The best matching data structure here would be a trie of chromosome prefixes but since
// the programs are orders of magnitude larger than the prefixes, it does not really matter.
// A map should be good enough.
std::map<std::string, CacheEntry> m_entries;
Program m_program;
size_t m_currentRound = 0;
size_t m_hits = 0;
size_t m_misses = 0;
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};
}