mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
129 lines
4.6 KiB
C++
129 lines
4.6 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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* Optimiser component that removes stores to memory and storage slots that are not used
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* or overwritten later on.
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*/
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#pragma once
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#include <libyul/ASTForward.h>
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#include <libyul/optimiser/ASTWalker.h>
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#include <libyul/optimiser/OptimiserStep.h>
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#include <libyul/optimiser/Semantics.h>
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#include <libyul/optimiser/UnusedStoreBase.h>
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#include <libyul/optimiser/KnowledgeBase.h>
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#include <libevmasm/SemanticInformation.h>
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#include <map>
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#include <vector>
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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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* Optimizer component that removes sstore and memory store statements if conditions are met for their removal.
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* In case of an sstore, if all outgoing code paths revert (due to an explicit revert(), invalid(),
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* or infinite recursion) or lead to another ``sstore`` for which the optimizer can tell that it will overwrite the first store,
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* the statement will be removed.
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*
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* For memory store operations, things are generally simpler, at least in the outermost yul block as all such statements
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* will be removed if they are never read from in any code path. At function analysis level however, the approach is similar
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* to sstore, as we don't know whether the memory location will be read once we leave the function's scope,
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* so the statement will be removed only if all code code paths lead to a memory overwrite.
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*
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* The m_store member of UnusedStoreBase uses the key "m" for memory and "s" for storage stores.
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*
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* Best run in SSA form.
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*
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* Prerequisite: Disambiguator, ForLoopInitRewriter.
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*/
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class UnusedStoreEliminator: public UnusedStoreBase
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{
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public:
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static constexpr char const* name{"UnusedStoreEliminator"};
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static void run(OptimiserStepContext& _context, Block& _ast);
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explicit UnusedStoreEliminator(
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Dialect const& _dialect,
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std::map<YulString, SideEffects> const& _functionSideEffects,
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std::map<YulString, ControlFlowSideEffects> _controlFlowSideEffects,
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std::map<YulString, AssignedValue> const& _ssaValues,
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bool _ignoreMemory
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);
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using UnusedStoreBase::operator();
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void operator()(FunctionCall const& _functionCall) override;
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void operator()(FunctionDefinition const&) override;
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void operator()(Leave const&) override;
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using UnusedStoreBase::visit;
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void visit(Statement const& _statement) override;
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using Location = evmasm::SemanticInformation::Location;
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using Effect = evmasm::SemanticInformation::Effect;
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struct Operation
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{
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Location location;
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Effect effect;
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/// Start of affected area. Unknown if not provided.
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std::optional<YulString> start;
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/// Length of affected area, unknown if not provided.
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/// Unused for storage.
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std::optional<YulString> length;
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};
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private:
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std::set<Statement const*>& activeMemoryStores() { return m_activeStores["m"_yulstring]; }
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std::set<Statement const*>& activeStorageStores() { return m_activeStores["s"_yulstring]; }
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void shortcutNestedLoop(ActiveStores const&) override
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{
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// We might only need to do this for newly introduced stores in the loop.
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markActiveAsUsed();
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}
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void finalizeFunctionDefinition(FunctionDefinition const&) override
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{
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markActiveAsUsed();
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}
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std::vector<Operation> operationsFromFunctionCall(FunctionCall const& _functionCall) const;
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void applyOperation(Operation const& _operation);
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bool knownUnrelated(Operation const& _op1, Operation const& _op2) const;
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bool knownCovered(Operation const& _covered, Operation const& _covering) const;
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void markActiveAsUsed(std::optional<Location> _onlyLocation = std::nullopt);
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void clearActive(std::optional<Location> _onlyLocation = std::nullopt);
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std::optional<YulString> identifierNameIfSSA(Expression const& _expression) const;
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bool const m_ignoreMemory;
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std::map<YulString, SideEffects> const& m_functionSideEffects;
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std::map<YulString, ControlFlowSideEffects> m_controlFlowSideEffects;
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std::map<YulString, AssignedValue> const& m_ssaValues;
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std::map<Statement const*, Operation> m_storeOperations;
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KnowledgeBase mutable m_knowledgeBase;
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};
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}
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