mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
129 lines
4.2 KiB
C++
129 lines
4.2 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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#pragma once
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#include <libyul/ASTForward.h>
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#include <libyul/YulString.h>
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#include <libsolutil/Common.h>
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#include <libsolutil/Numeric.h>
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#include <map>
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#include <functional>
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namespace solidity::yul
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{
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struct Dialect;
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struct AssignedValue;
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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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* Requires a callback that returns the current value of the variable.
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* The value can change any time during the lifetime of the KnowledgeBase,
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* it will update its internal data structure accordingly.
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*
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* This means that the code the KnowledgeBase is used on does not need to be in SSA
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* form.
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* The only requirement is that the assigned values are movable expressions.
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*
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* There is a constructor to provide all SSA values right at the beginning.
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* If you use this, the KnowledgeBase will be slightly more efficient.
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*
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* Internally, tries to find groups of variables that have a mutual constant
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* difference and stores these differences always relative to a specific
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* representative variable of the group.
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*
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* There is a special group which is the constant values. Those use the
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* empty YulString as representative "variable".
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*/
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class KnowledgeBase
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{
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public:
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/// Constructor for arbitrary value callback that allows for variable values
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/// to change in between calls to functions of this class.
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KnowledgeBase(std::function<AssignedValue const*(YulString)> _variableValues):
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m_variableValues(std::move(_variableValues))
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{}
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/// Constructor to use if source code is in SSA form and values are constant.
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KnowledgeBase(std::map<YulString, AssignedValue> const& _ssaValues);
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bool knownToBeDifferent(YulString _a, YulString _b);
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std::optional<u256> differenceIfKnownConstant(YulString _a, YulString _b);
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bool knownToBeDifferentByAtLeast32(YulString _a, YulString _b);
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bool knownToBeZero(YulString _a);
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std::optional<u256> valueIfKnownConstant(YulString _a);
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std::optional<u256> valueIfKnownConstant(Expression const& _expression);
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private:
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/**
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* Constant offset relative to a reference variable, or absolute constant if the
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* reference variable is the empty YulString.
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*/
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struct VariableOffset
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{
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YulString reference;
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u256 offset;
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bool isAbsolute() const
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{
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return reference.empty();
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}
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std::optional<u256> absoluteValue() const
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{
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if (isAbsolute())
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return offset;
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else
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return std::nullopt;
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}
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};
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VariableOffset explore(YulString _var);
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std::optional<VariableOffset> explore(Expression const& _value);
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/// Retrieves the current value of a variable and potentially resets the variable if it is not up to date.
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Expression const* valueOf(YulString _var);
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/// Resets all information about the variable and removes it from its group,
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/// potentially finding a new representative.
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void reset(YulString _var);
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VariableOffset setOffset(YulString _variable, VariableOffset _value);
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/// If true, we can assume that variable values never change and skip some steps.
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bool m_valuesAreSSA = false;
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/// Callback to retrieve the current value of a variable.
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std::function<AssignedValue const*(YulString)> m_variableValues;
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/// Offsets for each variable to one representative per group.
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/// The empty string is the representative of the constant value zero.
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std::map<YulString, VariableOffset> m_offsets;
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/// Last known value of each variable we queried.
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std::map<YulString, Expression const*> m_lastKnownValue;
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/// For each representative, variables that use it to offset from.
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std::map<YulString, std::set<YulString>> m_groupMembers;
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};
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}
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