mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
109 lines
3.4 KiB
C++
109 lines
3.4 KiB
C++
/*
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This file is part of solidity.
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solidity is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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solidity is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with solidity. If not, see <http://www.gnu.org/licenses/>.
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*/
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// SPDX-License-Identifier: GPL-3.0
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/**
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* Class that can answer questions about values of variables and their relations.
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*/
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#include <libyul/optimiser/KnowledgeBase.h>
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#include <libyul/AST.h>
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#include <libyul/Utilities.h>
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#include <libyul/optimiser/SimplificationRules.h>
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#include <libyul/optimiser/DataFlowAnalyzer.h>
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#include <libsolutil/CommonData.h>
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#include <variant>
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using namespace std;
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using namespace solidity;
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using namespace solidity::yul;
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bool KnowledgeBase::knownToBeDifferent(YulString _a, YulString _b)
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{
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// Try to use the simplification rules together with the
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// current values to turn `sub(_a, _b)` into a nonzero constant.
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// If that fails, try `eq(_a, _b)`.
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if (optional<u256> difference = differenceIfKnownConstant(_a, _b))
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return difference != 0;
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Expression expr2 = simplify(FunctionCall{{}, {{}, "eq"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
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if (holds_alternative<Literal>(expr2))
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return valueOfLiteral(std::get<Literal>(expr2)) == 0;
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return false;
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}
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optional<u256> KnowledgeBase::differenceIfKnownConstant(YulString _a, YulString _b)
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{
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// Try to use the simplification rules together with the
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// current values to turn `sub(_a, _b)` into a constant.
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Expression expr1 = simplify(FunctionCall{{}, {{}, "sub"_yulstring}, util::make_vector<Expression>(Identifier{{}, _a}, Identifier{{}, _b})});
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if (Literal const* value = get_if<Literal>(&expr1))
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return valueOfLiteral(*value);
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return {};
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}
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bool KnowledgeBase::knownToBeDifferentByAtLeast32(YulString _a, YulString _b)
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{
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// Try to use the simplification rules together with the
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// current values to turn `sub(_a, _b)` into a constant whose absolute value is at least 32.
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if (optional<u256> difference = differenceIfKnownConstant(_a, _b))
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return difference >= 32 && difference <= u256(0) - 32;
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return false;
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}
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bool KnowledgeBase::knownToBeZero(YulString _a)
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{
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return valueIfKnownConstant(_a) == u256{};
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}
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optional<u256> KnowledgeBase::valueIfKnownConstant(YulString _a)
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{
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if (m_variableValues.count(_a))
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if (Literal const* literal = get_if<Literal>(m_variableValues.at(_a).value))
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return valueOfLiteral(*literal);
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return {};
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}
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Expression KnowledgeBase::simplify(Expression _expression)
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{
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m_counter = 0;
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return simplifyRecursively(move(_expression));
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}
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Expression KnowledgeBase::simplifyRecursively(Expression _expression)
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{
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if (m_counter++ > 100)
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return _expression;
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if (holds_alternative<FunctionCall>(_expression))
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for (Expression& arg: std::get<FunctionCall>(_expression).arguments)
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arg = simplifyRecursively(arg);
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if (auto match = SimplificationRules::findFirstMatch(_expression, m_dialect, m_variableValues))
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return simplifyRecursively(match->action().toExpression(debugDataOf(_expression)));
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return _expression;
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}
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