Split known state from common subexpression eliminator.

1 files changed, 278 insertions, 0 deletions

diff --git a/KnownState.cpp b/KnownState.cpp
new file mode 100644
index 00000000..244270fb
--- /dev/null
+++ b/KnownState.cpp
@@ -0,0 +1,278 @@
+/*
+	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 KnownState.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Contains knowledge about the state of the virtual machine at a specific instruction.
+ */
+
+#include "KnownState.h"
+#include <functional>
+#include <libdevcrypto/SHA3.h>
+#include <libevmasm/AssemblyItem.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+ostream& KnownState::stream(
+	ostream& _out,
+	map<int, Id> _initialStack,
+	map<int, Id> _targetStack
+) const
+{
+	auto streamExpressionClass = [this](ostream& _out, Id _id)
+	{
+		auto const& expr = m_expressionClasses->representative(_id);
+		_out << "  " << dec << _id << ": " << *expr.item;
+		if (expr.sequenceNumber)
+			_out << "@" << dec << expr.sequenceNumber;
+		_out << "(";
+		for (Id arg: expr.arguments)
+			_out << dec << arg << ",";
+		_out << ")" << endl;
+	};
+
+	_out << "Optimizer analysis:" << endl;
+	_out << "Final stack height: " << dec << m_stackHeight << endl;
+	_out << "Equivalence classes: " << endl;
+	for (Id eqClass = 0; eqClass < m_expressionClasses->size(); ++eqClass)
+		streamExpressionClass(_out, eqClass);
+
+	_out << "Initial stack: " << endl;
+	for (auto const& it: _initialStack)
+	{
+		_out << "  " << dec << it.first << ": ";
+		streamExpressionClass(_out, it.second);
+	}
+	_out << "Target stack: " << endl;
+	for (auto const& it: _targetStack)
+	{
+		_out << "  " << dec << it.first << ": ";
+		streamExpressionClass(_out, it.second);
+	}
+
+	return _out;
+}
+
+KnownState::StoreOperation KnownState::feedItem(AssemblyItem const& _item, bool _copyItem)
+{
+	StoreOperation op;
+	if (_item.type() != Operation)
+	{
+		assertThrow(_item.deposit() == 1, InvalidDeposit, "");
+		setStackElement(++m_stackHeight, m_expressionClasses->find(_item, {}, _copyItem));
+	}
+	else
+	{
+		Instruction instruction = _item.instruction();
+		InstructionInfo info = instructionInfo(instruction);
+		if (SemanticInformation::isDupInstruction(_item))
+			setStackElement(
+				m_stackHeight + 1,
+				stackElement(
+					m_stackHeight - int(instruction) + int(Instruction::DUP1),
+					_item.getLocation()
+				)
+			);
+		else if (SemanticInformation::isSwapInstruction(_item))
+			swapStackElements(
+				m_stackHeight,
+				m_stackHeight - 1 - int(instruction) + int(Instruction::SWAP1),
+				_item.getLocation()
+			);
+		else if (instruction != Instruction::POP)
+		{
+			vector<Id> arguments(info.args);
+			for (int i = 0; i < info.args; ++i)
+				arguments[i] = stackElement(m_stackHeight - i, _item.getLocation());
+			if (_item.instruction() == Instruction::SSTORE)
+				op = storeInStorage(arguments[0], arguments[1], _item.getLocation());
+			else if (_item.instruction() == Instruction::SLOAD)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					loadFromStorage(arguments[0], _item.getLocation())
+				);
+			else if (_item.instruction() == Instruction::MSTORE)
+				op = storeInMemory(arguments[0], arguments[1], _item.getLocation());
+			else if (_item.instruction() == Instruction::MLOAD)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					loadFromMemory(arguments[0], _item.getLocation())
+				);
+			else if (_item.instruction() == Instruction::SHA3)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					applySha3(arguments.at(0), arguments.at(1), _item.getLocation())
+				);
+			else
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					m_expressionClasses->find(_item, arguments, _copyItem)
+				);
+		}
+		m_stackHeight += _item.deposit();
+	}
+	return op;
+}
+
+ExpressionClasses::Id KnownState::stackElement(int _stackHeight, SourceLocation const& _location)
+{
+	if (m_stackElements.count(_stackHeight))
+		return m_stackElements.at(_stackHeight);
+	// Stack element not found (not assigned yet), create new equivalence class.
+	return m_stackElements[_stackHeight] = initialStackElement(_stackHeight, _location);
+}
+
+ExpressionClasses::Id KnownState::initialStackElement(
+	int _stackHeight,
+	SourceLocation const& _location
+)
+{
+	assertThrow(_stackHeight <= 0, OptimizerException, "Initial stack element of positive height requested.");
+	assertThrow(_stackHeight > -16, StackTooDeepException, "");
+	// This is a special assembly item that refers to elements pre-existing on the initial stack.
+	return m_expressionClasses->find(AssemblyItem(dupInstruction(1 - _stackHeight), _location));
+}
+
+void KnownState::setStackElement(int _stackHeight, Id _class)
+{
+	m_stackElements[_stackHeight] = _class;
+}
+
+void KnownState::swapStackElements(
+	int _stackHeightA,
+	int _stackHeightB,
+	SourceLocation const& _location
+)
+{
+	assertThrow(_stackHeightA != _stackHeightB, OptimizerException, "Swap on same stack elements.");
+	// ensure they are created
+	stackElement(_stackHeightA, _location);
+	stackElement(_stackHeightB, _location);
+
+	swap(m_stackElements[_stackHeightA], m_stackElements[_stackHeightB]);
+}
+
+KnownState::StoreOperation KnownState::storeInStorage(
+	Id _slot,
+	Id _value,
+	SourceLocation const& _location)
+{
+	if (m_storageContent.count(_slot) && m_storageContent[_slot] == _value)
+		// do not execute the storage if we know that the value is already there
+		return StoreOperation();
+	m_sequenceNumber++;
+	decltype(m_storageContent) storageContents;
+	// Copy over all values (i.e. retain knowledge about them) where we know that this store
+	// operation will not destroy the knowledge. Specifically, we copy storage locations we know
+	// are different from _slot or locations where we know that the stored value is equal to _value.
+	for (auto const& storageItem: m_storageContent)
+		if (m_expressionClasses->knownToBeDifferent(storageItem.first, _slot) || storageItem.second == _value)
+			storageContents.insert(storageItem);
+	m_storageContent = move(storageContents);
+
+	AssemblyItem item(Instruction::SSTORE, _location);
+	Id id = m_expressionClasses->find(item, {_slot, _value}, true, m_sequenceNumber);
+	StoreOperation operation(StoreOperation::Storage, _slot, m_sequenceNumber, id);
+	m_storageContent[_slot] = _value;
+	// increment a second time so that we get unique sequence numbers for writes
+	m_sequenceNumber++;
+
+	return operation;
+}
+
+ExpressionClasses::Id KnownState::loadFromStorage(Id _slot, SourceLocation const& _location)
+{
+	if (m_storageContent.count(_slot))
+		return m_storageContent.at(_slot);
+
+	AssemblyItem item(Instruction::SLOAD, _location);
+	return m_storageContent[_slot] = m_expressionClasses->find(item, {_slot}, true, m_sequenceNumber);
+}
+
+KnownState::StoreOperation KnownState::storeInMemory(Id _slot, Id _value, SourceLocation const& _location)
+{
+	if (m_memoryContent.count(_slot) && m_memoryContent[_slot] == _value)
+		// do not execute the store if we know that the value is already there
+		return StoreOperation();
+	m_sequenceNumber++;
+	decltype(m_memoryContent) memoryContents;
+	// copy over values at points where we know that they are different from _slot by at least 32
+	for (auto const& memoryItem: m_memoryContent)
+		if (m_expressionClasses->knownToBeDifferentBy32(memoryItem.first, _slot))
+			memoryContents.insert(memoryItem);
+	m_memoryContent = move(memoryContents);
+
+	AssemblyItem item(Instruction::MSTORE, _location);
+	Id id = m_expressionClasses->find(item, {_slot, _value}, true, m_sequenceNumber);
+	StoreOperation operation(StoreOperation(StoreOperation::Memory, _slot, m_sequenceNumber, id));
+	m_memoryContent[_slot] = _value;
+	// increment a second time so that we get unique sequence numbers for writes
+	m_sequenceNumber++;
+	return operation;
+}
+
+ExpressionClasses::Id KnownState::loadFromMemory(Id _slot, SourceLocation const& _location)
+{
+	if (m_memoryContent.count(_slot))
+		return m_memoryContent.at(_slot);
+
+	AssemblyItem item(Instruction::MLOAD, _location);
+	return m_memoryContent[_slot] = m_expressionClasses->find(item, {_slot}, true, m_sequenceNumber);
+}
+
+KnownState::Id KnownState::applySha3(
+	Id _start,
+	Id _length,
+	SourceLocation const& _location
+)
+{
+	AssemblyItem sha3Item(Instruction::SHA3, _location);
+	// Special logic if length is a short constant, otherwise we cannot tell.
+	u256 const* l = m_expressionClasses->knownConstant(_length);
+	// unknown or too large length
+	if (!l || *l > 128)
+		return m_expressionClasses->find(sha3Item, {_start, _length}, true, m_sequenceNumber);
+
+	vector<Id> arguments;
+	for (u256 i = 0; i < *l; i += 32)
+	{
+		Id slot = m_expressionClasses->find(
+			AssemblyItem(Instruction::ADD, _location),
+			{_start, m_expressionClasses->find(i)}
+		);
+		arguments.push_back(loadFromMemory(slot, _location));
+	}
+	if (m_knownSha3Hashes.count(arguments))
+		return m_knownSha3Hashes.at(arguments);
+	Id v;
+	// If all arguments are known constants, compute the sha3 here
+	if (all_of(arguments.begin(), arguments.end(), [this](Id _a) { return !!m_expressionClasses->knownConstant(_a); }))
+	{
+		bytes data;
+		for (Id a: arguments)
+			data += toBigEndian(*m_expressionClasses->knownConstant(a));
+		data.resize(size_t(*l));
+		v = m_expressionClasses->find(AssemblyItem(u256(sha3(data)), _location));
+	}
+	else
+		v = m_expressionClasses->find(sha3Item, {_start, _length}, true, m_sequenceNumber);
+	return m_knownSha3Hashes[arguments] = v;
+}
+