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