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120 lines
3.4 KiB
120 lines
3.4 KiB
/*
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This file is part of cpp-ethereum.
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cpp-ethereum 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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cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @file ControlFlowGraph.h
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* @author Christian <c@ethdev.com>
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* @date 2015
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* Control flow analysis for the optimizer.
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*/
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#pragma once
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#include <vector>
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#include <memory>
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#include <libdevcore/Common.h>
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#include <libdevcore/Assertions.h>
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#include <libevmasm/ExpressionClasses.h>
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namespace dev
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{
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namespace eth
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{
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class KnownState;
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using KnownStatePointer = std::shared_ptr<KnownState>;
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/**
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* Identifier for a block, coincides with the tag number of an AssemblyItem but adds a special
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* ID for the inital block.
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*/
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class BlockId
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{
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public:
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BlockId() { *this = invalid(); }
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explicit BlockId(unsigned _id): m_id(_id) {}
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explicit BlockId(u256 const& _id);
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static BlockId initial() { return BlockId(-2); }
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static BlockId invalid() { return BlockId(-1); }
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bool operator==(BlockId const& _other) const { return m_id == _other.m_id; }
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bool operator!=(BlockId const& _other) const { return m_id != _other.m_id; }
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bool operator<(BlockId const& _other) const { return m_id < _other.m_id; }
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explicit operator bool() const { return *this != invalid(); }
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private:
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unsigned m_id;
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};
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/**
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* Control flow block inside which instruction counter is always incremented by one
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* (except for possibly the last instruction).
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*/
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struct BasicBlock
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{
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/// Start index into assembly item list.
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unsigned begin = 0;
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/// End index (excluded) inte assembly item list.
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unsigned end = 0;
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/// Tags pushed inside this block, with multiplicity.
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std::vector<BlockId> pushedTags;
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/// ID of the block that always follows this one (either non-branching part of JUMPI or flow
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/// into new block), or BlockId::invalid() otherwise
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BlockId next = BlockId::invalid();
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/// ID of the block that has to precede this one (because control flows into it).
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BlockId prev = BlockId::invalid();
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enum class EndType { JUMP, JUMPI, STOP, HANDOVER };
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EndType endType = EndType::HANDOVER;
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/// Knowledge about the state when this block is entered. Intersection of all possible ways
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/// to enter this block.
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KnownStatePointer startState;
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/// Knowledge about the state at the end of this block.
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KnownStatePointer endState;
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};
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using BasicBlocks = std::vector<BasicBlock>;
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class ControlFlowGraph
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{
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public:
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/// Initializes the control flow graph.
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/// @a _items has to persist across the usage of this class.
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ControlFlowGraph(AssemblyItems const& _items): m_items(_items) {}
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/// @returns vector of basic blocks in the order they should be used in the final code.
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/// Should be called only once.
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BasicBlocks optimisedBlocks();
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private:
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void findLargestTag();
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void splitBlocks();
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void resolveNextLinks();
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void removeUnusedBlocks();
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void gatherKnowledge();
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void setPrevLinks();
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BasicBlocks rebuildCode();
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BlockId generateNewId();
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unsigned m_lastUsedId = 0;
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AssemblyItems const& m_items;
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std::map<BlockId, BasicBlock> m_blocks;
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};
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}
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}
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