solidity/libyul/optimiser/ReasoningBasedSimplifier.h

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2020-05-11 17:56:29 +00:00
/*
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/>.
*/
#pragma once
#include <libyul/optimiser/ASTWalker.h>
#include <libyul/optimiser/OptimiserStep.h>
#include <libyul/Dialect.h>
// because of instruction
#include <libyul/backends/evm/EVMDialect.h>
#include <map>
namespace solidity::smtutil
{
class SolverInterface;
class Expression;
struct Sort;
}
namespace solidity::yul
{
/**
* Reasoning-based simplifier.
* This optimizer uses SMT solvers to check whether `if` conditions are constant.
* - If `constraints AND condition` is UNSAT, the condition is never true and the whole body can be removed.
* - If `constraints AND NOT condition` is UNSAT, the condition is always true and can be replaced by `1`.
* The simplifications above can only be applied if the condition is movable.
*
* It is only effective on the EVM dialect, but safe to use on other dialects.
*
* Prerequisite: Disambiguator, SSATransform.
*/
class ReasoningBasedSimplifier: public ASTModifier
{
public:
static constexpr char const* name{"ReasoningBasedSimplifier"};
static void run(OptimiserStepContext& _context, Block& _ast);
static std::optional<std::string> invalidInCurrentEnvironment();
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using ASTModifier::operator();
void operator()(VariableDeclaration& _varDecl) override;
void operator()(If& _if) override;
private:
explicit ReasoningBasedSimplifier(
Dialect const& _dialect,
std::set<YulString> const& _ssaVariables
);
smtutil::Expression encodeExpression(
Expression const& _expression
);
virtual smtutil::Expression encodeEVMBuiltin(
evmasm::Instruction _instruction,
std::vector<Expression> const& _arguments
);
smtutil::Expression int2bv(smtutil::Expression _arg) const;
smtutil::Expression bv2int(smtutil::Expression _arg) const;
smtutil::Expression newVariable();
virtual smtutil::Expression newRestrictedVariable();
std::string uniqueName();
virtual std::shared_ptr<smtutil::Sort> defaultSort() const;
virtual smtutil::Expression booleanValue(smtutil::Expression _value) const;
virtual smtutil::Expression constantValue(size_t _value) const;
virtual smtutil::Expression literalValue(Literal const& _literal) const;
virtual smtutil::Expression unsignedToSigned(smtutil::Expression _value);
virtual smtutil::Expression signedToUnsigned(smtutil::Expression _value);
virtual smtutil::Expression wrap(smtutil::Expression _value);
Dialect const& m_dialect;
std::set<YulString> const& m_ssaVariables;
std::unique_ptr<smtutil::SolverInterface> m_solver;
std::map<YulString, smtutil::Expression> m_variables;
size_t m_varCounter = 0;
};
}