move libevmasm

29 files changed, 5102 insertions, 0 deletions

diff --git a/libevmasm/Assembly.cpp b/libevmasm/Assembly.cpp
new file mode 100644
index 00000000..7277865e
--- /dev/null
+++ b/libevmasm/Assembly.cpp
@@ -0,0 +1,545 @@
+/*
+	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 Assembly.cpp
+ * @author Gav Wood <i@gavwood.com>
+ * @date 2014
+ */
+
+#include "Assembly.h"
+#include <fstream>
+#include <libdevcore/Log.h>
+#include <libevmasm/CommonSubexpressionEliminator.h>
+#include <libevmasm/ControlFlowGraph.h>
+#include <libevmasm/BlockDeduplicator.h>
+#include <libevmasm/ConstantOptimiser.h>
+#include <libevmasm/GasMeter.h>
+#include <json/json.h>
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+void Assembly::append(Assembly const& _a)
+{
+	auto newDeposit = m_deposit + _a.deposit();
+	for (AssemblyItem i: _a.m_items)
+	{
+		if (i.type() == Tag || i.type() == PushTag)
+			i.setData(i.data() + m_usedTags);
+		else if (i.type() == PushSub || i.type() == PushSubSize)
+			i.setData(i.data() + m_subs.size());
+		append(i);
+	}
+	m_deposit = newDeposit;
+	m_usedTags += _a.m_usedTags;
+	for (auto const& i: _a.m_data)
+		m_data.insert(i);
+	for (auto const& i: _a.m_strings)
+		m_strings.insert(i);
+	m_subs += _a.m_subs;
+	for (auto const& lib: _a.m_libraries)
+		m_libraries.insert(lib);
+
+	assert(!_a.m_baseDeposit);
+	assert(!_a.m_totalDeposit);
+}
+
+void Assembly::append(Assembly const& _a, int _deposit)
+{
+	if (_deposit > _a.m_deposit)
+		BOOST_THROW_EXCEPTION(InvalidDeposit());
+	else
+	{
+		append(_a);
+		while (_deposit++ < _a.m_deposit)
+			append(Instruction::POP);
+	}
+}
+
+string Assembly::out() const
+{
+	stringstream ret;
+	stream(ret);
+	return ret.str();
+}
+
+unsigned Assembly::bytesRequired() const
+{
+	for (unsigned br = 1;; ++br)
+	{
+		unsigned ret = 1;
+		for (auto const& i: m_data)
+			ret += i.second.size();
+
+		for (AssemblyItem const& i: m_items)
+			ret += i.bytesRequired(br);
+		if (dev::bytesRequired(ret) <= br)
+			return ret;
+	}
+}
+
+string Assembly::locationFromSources(StringMap const& _sourceCodes, SourceLocation const& _location) const
+{
+	if (_location.isEmpty() || _sourceCodes.empty() || _location.start >= _location.end || _location.start < 0)
+		return "";
+
+	auto it = _sourceCodes.find(*_location.sourceName);
+	if (it == _sourceCodes.end())
+		return "";
+
+	string const& source = it->second;
+	if (size_t(_location.start) >= source.size())
+		return "";
+
+	string cut = source.substr(_location.start, _location.end - _location.start);
+	auto newLinePos = cut.find_first_of("\n");
+	if (newLinePos != string::npos)
+		cut = cut.substr(0, newLinePos) + "...";
+
+	return cut;
+}
+
+ostream& Assembly::streamAsm(ostream& _out, string const& _prefix, StringMap const& _sourceCodes) const
+{
+	_out << _prefix << ".code:" << endl;
+	for (AssemblyItem const& i: m_items)
+	{
+		_out << _prefix;
+		switch (i.type())
+		{
+		case Operation:
+			_out << "  " << instructionInfo(i.instruction()).name  << "\t" << i.getJumpTypeAsString();
+			break;
+		case Push:
+			_out << "  PUSH " << hex << i.data();
+			break;
+		case PushString:
+			_out << "  PUSH \"" << m_strings.at((h256)i.data()) << "\"";
+			break;
+		case PushTag:
+			if (i.data() == 0)
+				_out << "  PUSH [ErrorTag]";
+			else
+				_out << "  PUSH [tag" << dec << i.data() << "]";
+			break;
+		case PushSub:
+			_out << "  PUSH [$" << h256(i.data()).abridgedMiddle() << "]";
+			break;
+		case PushSubSize:
+			_out << "  PUSH #[$" << h256(i.data()).abridgedMiddle() << "]";
+			break;
+		case PushProgramSize:
+			_out << "  PUSHSIZE";
+			break;
+		case PushLibraryAddress:
+			_out << "  PUSHLIB \"" << m_libraries.at(h256(i.data())) << "\"";
+			break;
+		case Tag:
+			_out << "tag" << dec << i.data() << ": " << endl << _prefix << "  JUMPDEST";
+			break;
+		case PushData:
+			_out << "  PUSH [" << hex << (unsigned)i.data() << "]";
+			break;
+		default:
+			BOOST_THROW_EXCEPTION(InvalidOpcode());
+		}
+		_out << "\t\t" << locationFromSources(_sourceCodes, i.location()) << endl;
+	}
+
+	if (!m_data.empty() || !m_subs.empty())
+	{
+		_out << _prefix << ".data:" << endl;
+		for (auto const& i: m_data)
+			if (u256(i.first) >= m_subs.size())
+				_out << _prefix << "  " << hex << (unsigned)(u256)i.first << ": " << dev::toHex(i.second) << endl;
+		for (size_t i = 0; i < m_subs.size(); ++i)
+		{
+			_out << _prefix << "  " << hex << i << ": " << endl;
+			m_subs[i].stream(_out, _prefix + "  ", _sourceCodes);
+		}
+	}
+	return _out;
+}
+
+Json::Value Assembly::createJsonValue(string _name, int _begin, int _end, string _value, string _jumpType) const
+{
+	Json::Value value;
+	value["name"] = _name;
+	value["begin"] = _begin;
+	value["end"] = _end;
+	if (!_value.empty())
+		value["value"] = _value;
+	if (!_jumpType.empty())
+		value["jumpType"] = _jumpType;
+	return value;
+}
+
+string toStringInHex(u256 _value)
+{
+	std::stringstream hexStr;
+	hexStr << hex << _value;
+	return hexStr.str();
+}
+
+Json::Value Assembly::streamAsmJson(ostream& _out, StringMap const& _sourceCodes) const
+{
+	Json::Value root;
+
+	Json::Value collection(Json::arrayValue);
+	for (AssemblyItem const& i: m_items)
+	{
+		switch (i.type())
+		{
+		case Operation:
+			collection.append(
+				createJsonValue(instructionInfo(i.instruction()).name, i.location().start, i.location().end, i.getJumpTypeAsString()));
+			break;
+		case Push:
+			collection.append(
+				createJsonValue("PUSH", i.location().start, i.location().end, toStringInHex(i.data()), i.getJumpTypeAsString()));
+			break;
+		case PushString:
+			collection.append(
+				createJsonValue("PUSH tag", i.location().start, i.location().end, m_strings.at((h256)i.data())));
+			break;
+		case PushTag:
+			if (i.data() == 0)
+				collection.append(
+					createJsonValue("PUSH [ErrorTag]", i.location().start, i.location().end, ""));
+			else
+				collection.append(
+					createJsonValue("PUSH [tag]", i.location().start, i.location().end, string(i.data())));
+			break;
+		case PushSub:
+			collection.append(
+				createJsonValue("PUSH [$]", i.location().start, i.location().end, dev::toString(h256(i.data()))));
+			break;
+		case PushSubSize:
+			collection.append(
+				createJsonValue("PUSH #[$]", i.location().start, i.location().end, dev::toString(h256(i.data()))));
+			break;
+		case PushProgramSize:
+			collection.append(
+				createJsonValue("PUSHSIZE", i.location().start, i.location().end));
+			break;
+		case PushLibraryAddress:
+			collection.append(
+				createJsonValue("PUSHLIB", i.location().start, i.location().end, m_libraries.at(h256(i.data())))
+			);
+			break;
+		case Tag:
+			collection.append(
+				createJsonValue("tag", i.location().start, i.location().end, string(i.data())));
+			collection.append(
+				createJsonValue("JUMPDEST", i.location().start, i.location().end));
+			break;
+		case PushData:
+			collection.append(createJsonValue("PUSH data", i.location().start, i.location().end, toStringInHex(i.data())));
+			break;
+		default:
+			BOOST_THROW_EXCEPTION(InvalidOpcode());
+		}
+	}
+
+	root[".code"] = collection;
+
+	if (!m_data.empty() || !m_subs.empty())
+	{
+		Json::Value data;
+		for (auto const& i: m_data)
+			if (u256(i.first) >= m_subs.size())
+				data[toStringInHex((u256)i.first)] = toHex(i.second);
+
+		for (size_t i = 0; i < m_subs.size(); ++i)
+		{
+			std::stringstream hexStr;
+			hexStr << hex << i;
+			data[hexStr.str()] = m_subs[i].stream(_out, "", _sourceCodes, true);
+		}
+		root[".data"] = data;
+		_out << root;
+	}
+	return root;
+}
+
+Json::Value Assembly::stream(ostream& _out, string const& _prefix, StringMap const& _sourceCodes, bool _inJsonFormat) const
+{
+	if (_inJsonFormat)
+		return streamAsmJson(_out, _sourceCodes);
+	else
+	{
+		streamAsm(_out, _prefix, _sourceCodes);
+		return Json::Value();
+	}
+}
+
+AssemblyItem const& Assembly::append(AssemblyItem const& _i)
+{
+	m_deposit += _i.deposit();
+	m_items.push_back(_i);
+	if (m_items.back().location().isEmpty() && !m_currentSourceLocation.isEmpty())
+		m_items.back().setLocation(m_currentSourceLocation);
+	return back();
+}
+
+AssemblyItem Assembly::newPushLibraryAddress(string const& _identifier)
+{
+	h256 h(dev::sha3(_identifier));
+	m_libraries[h] = _identifier;
+	return AssemblyItem(PushLibraryAddress, h);
+}
+
+void Assembly::injectStart(AssemblyItem const& _i)
+{
+	m_items.insert(m_items.begin(), _i);
+}
+
+struct OptimiserChannel: public LogChannel { static const char* name() { return "OPT"; } static const int verbosity = 12; };
+#define copt dev::LogOutputStream<OptimiserChannel, true>()
+
+Assembly& Assembly::optimise(bool _enable, bool _isCreation, size_t _runs)
+{
+	if (!_enable)
+		return *this;
+
+	unsigned total = 0;
+	for (unsigned count = 1; count > 0; total += count)
+	{
+		copt << toString(*this);
+		count = 0;
+
+		copt << "Performing optimisation...";
+		// This only modifies PushTags, we have to run again to actually remove code.
+		BlockDeduplicator dedup(m_items);
+		if (dedup.deduplicate())
+			count++;
+
+		{
+			ControlFlowGraph cfg(m_items);
+			AssemblyItems optimisedItems;
+			for (BasicBlock const& block: cfg.optimisedBlocks())
+			{
+				assertThrow(!!block.startState, OptimizerException, "");
+				CommonSubexpressionEliminator eliminator(*block.startState);
+				auto iter = m_items.begin() + block.begin;
+				auto const end = m_items.begin() + block.end;
+				while (iter < end)
+				{
+					auto orig = iter;
+					iter = eliminator.feedItems(iter, end);
+					bool shouldReplace = false;
+					AssemblyItems optimisedChunk;
+					try
+					{
+						optimisedChunk = eliminator.getOptimizedItems();
+						shouldReplace = (optimisedChunk.size() < size_t(iter - orig));
+					}
+					catch (StackTooDeepException const&)
+					{
+						// This might happen if the opcode reconstruction is not as efficient
+						// as the hand-crafted code.
+					}
+					catch (ItemNotAvailableException const&)
+					{
+						// This might happen if e.g. associativity and commutativity rules
+						// reorganise the expression tree, but not all leaves are available.
+					}
+
+					if (shouldReplace)
+					{
+						copt << "Old size: " << (iter - orig) << ", new size: " << optimisedChunk.size();
+						count++;
+						optimisedItems += optimisedChunk;
+					}
+					else
+						copy(orig, iter, back_inserter(optimisedItems));
+				}
+			}
+
+			if (optimisedItems.size() < m_items.size())
+			{
+				m_items = move(optimisedItems);
+				count++;
+			}
+		}
+	}
+
+	total += ConstantOptimisationMethod::optimiseConstants(
+		_isCreation,
+		_isCreation ? 1 : _runs,
+		*this,
+		m_items
+	);
+
+	copt << total << " optimisations done.";
+
+	for (auto& sub: m_subs)
+	  sub.optimise(true, false, _runs);
+
+	return *this;
+}
+
+LinkerObject const& Assembly::assemble() const
+{
+	if (!m_assembledObject.bytecode.empty())
+		return m_assembledObject;
+
+	LinkerObject& ret = m_assembledObject;
+
+	unsigned totalBytes = bytesRequired();
+	vector<unsigned> tagPos(m_usedTags);
+	map<unsigned, unsigned> tagRef;
+	multimap<h256, unsigned> dataRef;
+	multimap<size_t, size_t> subRef;
+	vector<unsigned> sizeRef; ///< Pointers to code locations where the size of the program is inserted
+	unsigned bytesPerTag = dev::bytesRequired(totalBytes);
+	byte tagPush = (byte)Instruction::PUSH1 - 1 + bytesPerTag;
+
+	unsigned bytesRequiredIncludingData = bytesRequired();
+	for (auto const& sub: m_subs)
+		bytesRequiredIncludingData += sub.assemble().bytecode.size();
+
+	unsigned bytesPerDataRef = dev::bytesRequired(bytesRequiredIncludingData);
+	byte dataRefPush = (byte)Instruction::PUSH1 - 1 + bytesPerDataRef;
+	ret.bytecode.reserve(bytesRequiredIncludingData);
+
+	for (AssemblyItem const& i: m_items)
+	{
+		// store position of the invalid jump destination
+		if (i.type() != Tag && tagPos[0] == 0)
+			tagPos[0] = ret.bytecode.size();
+
+		switch (i.type())
+		{
+		case Operation:
+			ret.bytecode.push_back((byte)i.data());
+			break;
+		case PushString:
+		{
+			ret.bytecode.push_back((byte)Instruction::PUSH32);
+			unsigned ii = 0;
+			for (auto j: m_strings.at((h256)i.data()))
+				if (++ii > 32)
+					break;
+				else
+					ret.bytecode.push_back((byte)j);
+			while (ii++ < 32)
+				ret.bytecode.push_back(0);
+			break;
+		}
+		case Push:
+		{
+			byte b = max<unsigned>(1, dev::bytesRequired(i.data()));
+			ret.bytecode.push_back((byte)Instruction::PUSH1 - 1 + b);
+			ret.bytecode.resize(ret.bytecode.size() + b);
+			bytesRef byr(&ret.bytecode.back() + 1 - b, b);
+			toBigEndian(i.data(), byr);
+			break;
+		}
+		case PushTag:
+		{
+			ret.bytecode.push_back(tagPush);
+			tagRef[ret.bytecode.size()] = (unsigned)i.data();
+			ret.bytecode.resize(ret.bytecode.size() + bytesPerTag);
+			break;
+		}
+		case PushData:
+			ret.bytecode.push_back(dataRefPush);
+			dataRef.insert(make_pair((h256)i.data(), ret.bytecode.size()));
+			ret.bytecode.resize(ret.bytecode.size() + bytesPerDataRef);
+			break;
+		case PushSub:
+			ret.bytecode.push_back(dataRefPush);
+			subRef.insert(make_pair(size_t(i.data()), ret.bytecode.size()));
+			ret.bytecode.resize(ret.bytecode.size() + bytesPerDataRef);
+			break;
+		case PushSubSize:
+		{
+			auto s = m_subs.at(size_t(i.data())).assemble().bytecode.size();
+			i.setPushedValue(u256(s));
+			byte b = max<unsigned>(1, dev::bytesRequired(s));
+			ret.bytecode.push_back((byte)Instruction::PUSH1 - 1 + b);
+			ret.bytecode.resize(ret.bytecode.size() + b);
+			bytesRef byr(&ret.bytecode.back() + 1 - b, b);
+			toBigEndian(s, byr);
+			break;
+		}
+		case PushProgramSize:
+		{
+			ret.bytecode.push_back(dataRefPush);
+			sizeRef.push_back(ret.bytecode.size());
+			ret.bytecode.resize(ret.bytecode.size() + bytesPerDataRef);
+			break;
+		}
+		case PushLibraryAddress:
+			ret.bytecode.push_back(byte(Instruction::PUSH20));
+			ret.linkReferences[ret.bytecode.size()] = m_libraries.at(i.data());
+			ret.bytecode.resize(ret.bytecode.size() + 20);
+			break;
+		case Tag:
+			tagPos[(unsigned)i.data()] = ret.bytecode.size();
+			assertThrow(i.data() != 0, AssemblyException, "");
+			ret.bytecode.push_back((byte)Instruction::JUMPDEST);
+			break;
+		default:
+			BOOST_THROW_EXCEPTION(InvalidOpcode());
+		}
+	}
+	for (auto const& i: tagRef)
+	{
+		bytesRef r(ret.bytecode.data() + i.first, bytesPerTag);
+		auto tag = i.second;
+		if (tag >= tagPos.size())
+			tag = 0;
+		if (tag == 0)
+			assertThrow(tagPos[tag] != 0, AssemblyException, "");
+
+		toBigEndian(tagPos[tag], r);
+	}
+
+	if (!dataRef.empty() && !subRef.empty())
+		ret.bytecode.push_back(0);
+	for (size_t i = 0; i < m_subs.size(); ++i)
+	{
+		auto references = subRef.equal_range(i);
+		if (references.first == references.second)
+			continue;
+		for (auto ref = references.first; ref != references.second; ++ref)
+		{
+			bytesRef r(ret.bytecode.data() + ref->second, bytesPerDataRef);
+			toBigEndian(ret.bytecode.size(), r);
+		}
+		ret.append(m_subs[i].assemble());
+	}
+	for (auto const& dataItem: m_data)
+	{
+		auto references = dataRef.equal_range(dataItem.first);
+		if (references.first == references.second)
+			continue;
+		for (auto ref = references.first; ref != references.second; ++ref)
+		{
+			bytesRef r(ret.bytecode.data() + ref->second, bytesPerDataRef);
+			toBigEndian(ret.bytecode.size(), r);
+		}
+		ret.bytecode += dataItem.second;
+	}
+	for (unsigned pos: sizeRef)
+	{
+		bytesRef r(ret.bytecode.data() + pos, bytesPerDataRef);
+		toBigEndian(ret.bytecode.size(), r);
+	}
+	return ret;
+}
diff --git a/libevmasm/Assembly.h b/libevmasm/Assembly.h
new file mode 100644
index 00000000..28328277
--- /dev/null
+++ b/libevmasm/Assembly.h
@@ -0,0 +1,151 @@
+/*
+	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 Assembly.h
+ * @author Gav Wood <i@gavwood.com>
+ * @date 2014
+ */
+
+#pragma once
+
+#include <iostream>
+#include <sstream>
+#include <libdevcore/Common.h>
+#include <libdevcore/Assertions.h>
+#include <libdevcore/SHA3.h>
+#include <libevmcore/Instruction.h>
+#include <libevmasm/SourceLocation.h>
+#include <libevmasm/AssemblyItem.h>
+#include <libevmasm/LinkerObject.h>
+#include "Exceptions.h"
+#include <json/json.h>
+
+namespace Json
+{
+class Value;
+}
+namespace dev
+{
+namespace eth
+{
+
+class Assembly
+{
+public:
+	Assembly() {}
+
+	AssemblyItem newTag() { return AssemblyItem(Tag, m_usedTags++); }
+	AssemblyItem newPushTag() { return AssemblyItem(PushTag, m_usedTags++); }
+	AssemblyItem newData(bytes const& _data) { h256 h(sha3(asString(_data))); m_data[h] = _data; return AssemblyItem(PushData, h); }
+	AssemblyItem newSub(Assembly const& _sub) { m_subs.push_back(_sub); return AssemblyItem(PushSub, m_subs.size() - 1); }
+	Assembly const& sub(size_t _sub) const { return m_subs.at(_sub); }
+	Assembly& sub(size_t _sub) { return m_subs.at(_sub); }
+	AssemblyItem newPushString(std::string const& _data) { h256 h(sha3(_data)); m_strings[h] = _data; return AssemblyItem(PushString, h); }
+	AssemblyItem newPushSubSize(u256 const& _subId) { return AssemblyItem(PushSubSize, _subId); }
+	AssemblyItem newPushLibraryAddress(std::string const& _identifier);
+
+	AssemblyItem append() { return append(newTag()); }
+	void append(Assembly const& _a);
+	void append(Assembly const& _a, int _deposit);
+	AssemblyItem const& append(AssemblyItem const& _i);
+	AssemblyItem const& append(std::string const& _data) { return append(newPushString(_data)); }
+	AssemblyItem const& append(bytes const& _data) { return append(newData(_data)); }
+	AssemblyItem appendSubSize(Assembly const& _a) { auto ret = newSub(_a); append(newPushSubSize(ret.data())); return ret; }
+	/// Pushes the final size of the current assembly itself. Use this when the code is modified
+	/// after compilation and CODESIZE is not an option.
+	void appendProgramSize() { append(AssemblyItem(PushProgramSize)); }
+	void appendLibraryAddress(std::string const& _identifier) { append(newPushLibraryAddress(_identifier)); }
+
+	AssemblyItem appendJump() { auto ret = append(newPushTag()); append(Instruction::JUMP); return ret; }
+	AssemblyItem appendJumpI() { auto ret = append(newPushTag()); append(Instruction::JUMPI); return ret; }
+	AssemblyItem appendJump(AssemblyItem const& _tag) { auto ret = append(_tag.pushTag()); append(Instruction::JUMP); return ret; }
+	AssemblyItem appendJumpI(AssemblyItem const& _tag) { auto ret = append(_tag.pushTag()); append(Instruction::JUMPI); return ret; }
+	AssemblyItem errorTag() { return AssemblyItem(PushTag, 0); }
+
+	template <class T> Assembly& operator<<(T const& _d) { append(_d); return *this; }
+	AssemblyItems const& items() const { return m_items; }
+	AssemblyItem const& back() const { return m_items.back(); }
+	std::string backString() const { return m_items.size() && m_items.back().type() == PushString ? m_strings.at((h256)m_items.back().data()) : std::string(); }
+
+	void onePath() { if (asserts(!m_totalDeposit && !m_baseDeposit)) BOOST_THROW_EXCEPTION(InvalidDeposit()); m_baseDeposit = m_deposit; m_totalDeposit = INT_MAX; }
+	void otherPath() { donePath(); m_totalDeposit = m_deposit; m_deposit = m_baseDeposit; }
+	void donePaths() { donePath(); m_totalDeposit = m_baseDeposit = 0; }
+	void ignored() { m_baseDeposit = m_deposit; }
+	void endIgnored() { m_deposit = m_baseDeposit; m_baseDeposit = 0; }
+
+	void popTo(int _deposit) { while (m_deposit > _deposit) append(Instruction::POP); }
+
+	void injectStart(AssemblyItem const& _i);
+	std::string out() const;
+	int deposit() const { return m_deposit; }
+	void adjustDeposit(int _adjustment) { m_deposit += _adjustment; if (asserts(m_deposit >= 0)) BOOST_THROW_EXCEPTION(InvalidDeposit()); }
+	void setDeposit(int _deposit) { m_deposit = _deposit; if (asserts(m_deposit >= 0)) BOOST_THROW_EXCEPTION(InvalidDeposit()); }
+
+	/// Changes the source location used for each appended item.
+	void setSourceLocation(SourceLocation const& _location) { m_currentSourceLocation = _location; }
+
+	/// Assembles the assembly into bytecode. The assembly should not be modified after this call.
+	LinkerObject const& assemble() const;
+	bytes const& data(h256 const& _i) const { return m_data.at(_i); }
+
+	/// Modify (if @a _enable is set) and return the current assembly such that creation and
+	/// execution gas usage is optimised. @a _isCreation should be true for the top-level assembly.
+	/// @a _runs specifes an estimate on how often each opcode in this assembly will be executed,
+	/// i.e. use a small value to optimise for size and a large value to optimise for runtime.
+	Assembly& optimise(bool _enable, bool _isCreation = true, size_t _runs = 200);
+	Json::Value stream(
+		std::ostream& _out,
+		std::string const& _prefix = "",
+		const StringMap &_sourceCodes = StringMap(),
+		bool _inJsonFormat = false
+	) const;
+
+protected:
+	std::string locationFromSources(StringMap const& _sourceCodes, SourceLocation const& _location) const;
+	void donePath() { if (m_totalDeposit != INT_MAX && m_totalDeposit != m_deposit) BOOST_THROW_EXCEPTION(InvalidDeposit()); }
+	unsigned bytesRequired() const;
+
+private:
+	Json::Value streamAsmJson(std::ostream& _out, StringMap const& _sourceCodes) const;
+	std::ostream& streamAsm(std::ostream& _out, std::string const& _prefix, StringMap const& _sourceCodes) const;
+	Json::Value createJsonValue(std::string _name, int _begin, int _end, std::string _value = std::string(), std::string _jumpType = std::string()) const;
+
+protected:
+	// 0 is reserved for exception
+	unsigned m_usedTags = 1;
+	AssemblyItems m_items;
+	std::map<h256, bytes> m_data;
+	std::vector<Assembly> m_subs;
+	std::map<h256, std::string> m_strings;
+	std::map<h256, std::string> m_libraries; ///< Identifiers of libraries to be linked.
+
+	mutable LinkerObject m_assembledObject;
+
+	int m_deposit = 0;
+	int m_baseDeposit = 0;
+	int m_totalDeposit = 0;
+
+	SourceLocation m_currentSourceLocation;
+};
+
+inline std::ostream& operator<<(std::ostream& _out, Assembly const& _a)
+{
+	_a.stream(_out);
+	return _out;
+}
+
+}
+}
diff --git a/libevmasm/AssemblyItem.cpp b/libevmasm/AssemblyItem.cpp
new file mode 100644
index 00000000..d7051064
--- /dev/null
+++ b/libevmasm/AssemblyItem.cpp
@@ -0,0 +1,134 @@
+/*
+	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 Assembly.cpp
+ * @author Gav Wood <i@gavwood.com>
+ * @date 2014
+ */
+
+#include "AssemblyItem.h"
+#include <fstream>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+unsigned AssemblyItem::bytesRequired(unsigned _addressLength) const
+{
+	switch (m_type)
+	{
+	case Operation:
+	case Tag: // 1 byte for the JUMPDEST
+		return 1;
+	case PushString:
+		return 33;
+	case Push:
+		return 1 + max<unsigned>(1, dev::bytesRequired(m_data));
+	case PushSubSize:
+	case PushProgramSize:
+		return 4;		// worst case: a 16MB program
+	case PushTag:
+	case PushData:
+	case PushSub:
+		return 1 + _addressLength;
+	case PushLibraryAddress:
+		return 21;
+	default:
+		break;
+	}
+	BOOST_THROW_EXCEPTION(InvalidOpcode());
+}
+
+int AssemblyItem::deposit() const
+{
+	switch (m_type)
+	{
+	case Operation:
+		return instructionInfo(instruction()).ret - instructionInfo(instruction()).args;
+	case Push:
+	case PushString:
+	case PushTag:
+	case PushData:
+	case PushSub:
+	case PushSubSize:
+	case PushProgramSize:
+	case PushLibraryAddress:
+		return 1;
+	case Tag:
+		return 0;
+	default:;
+	}
+	return 0;
+}
+
+string AssemblyItem::getJumpTypeAsString() const
+{
+	switch (m_jumpType)
+	{
+	case JumpType::IntoFunction:
+		return "[in]";
+	case JumpType::OutOfFunction:
+		return "[out]";
+	case JumpType::Ordinary:
+	default:
+		return "";
+	}
+}
+
+ostream& dev::eth::operator<<(ostream& _out, AssemblyItem const& _item)
+{
+	switch (_item.type())
+	{
+	case Operation:
+		_out << " " << instructionInfo(_item.instruction()).name;
+		if (_item.instruction() == eth::Instruction::JUMP || _item.instruction() == eth::Instruction::JUMPI)
+			_out << "\t" << _item.getJumpTypeAsString();
+		break;
+	case Push:
+		_out << " PUSH " << hex << _item.data();
+		break;
+	case PushString:
+		_out << " PushString"  << hex << (unsigned)_item.data();
+		break;
+	case PushTag:
+		_out << " PushTag " << _item.data();
+		break;
+	case Tag:
+		_out << " Tag " << _item.data();
+		break;
+	case PushData:
+		_out << " PushData " << hex << (unsigned)_item.data();
+		break;
+	case PushSub:
+		_out << " PushSub " << hex << h256(_item.data()).abridgedMiddle();
+		break;
+	case PushSubSize:
+		_out << " PushSubSize " << hex << h256(_item.data()).abridgedMiddle();
+		break;
+	case PushProgramSize:
+		_out << " PushProgramSize";
+		break;
+	case PushLibraryAddress:
+		_out << " PushLibraryAddress " << hex << h256(_item.data()).abridgedMiddle();
+		break;
+	case UndefinedItem:
+		_out << " ???";
+		break;
+	default:
+		BOOST_THROW_EXCEPTION(InvalidOpcode());
+	}
+	return _out;
+}
diff --git a/libevmasm/AssemblyItem.h b/libevmasm/AssemblyItem.h
new file mode 100644
index 00000000..795b5a8a
--- /dev/null
+++ b/libevmasm/AssemblyItem.h
@@ -0,0 +1,123 @@
+/*
+	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 Assembly.h
+ * @author Gav Wood <i@gavwood.com>
+ * @date 2014
+ */
+
+#pragma once
+
+#include <iostream>
+#include <sstream>
+#include <libdevcore/Common.h>
+#include <libdevcore/Assertions.h>
+#include <libevmcore/Instruction.h>
+#include <libevmasm/SourceLocation.h>
+#include "Exceptions.h"
+
+namespace dev
+{
+namespace eth
+{
+
+enum AssemblyItemType {
+	UndefinedItem,
+	Operation,
+	Push,
+	PushString,
+	PushTag,
+	PushSub,
+	PushSubSize,
+	PushProgramSize,
+	Tag,
+	PushData,
+	PushLibraryAddress ///< Push a currently unknown address of another (library) contract.
+};
+
+class Assembly;
+
+class AssemblyItem
+{
+public:
+	enum class JumpType { Ordinary, IntoFunction, OutOfFunction };
+
+	AssemblyItem(u256 _push, SourceLocation const& _location = SourceLocation()):
+		AssemblyItem(Push, _push, _location) { }
+	AssemblyItem(Instruction _i, SourceLocation const& _location = SourceLocation()):
+		AssemblyItem(Operation, byte(_i), _location) { }
+	AssemblyItem(AssemblyItemType _type, u256 _data = 0, SourceLocation const& _location = SourceLocation()):
+		m_type(_type),
+		m_data(_data),
+		m_location(_location)
+	{
+	}
+
+	AssemblyItem tag() const { assertThrow(m_type == PushTag || m_type == Tag, Exception, ""); return AssemblyItem(Tag, m_data); }
+	AssemblyItem pushTag() const { assertThrow(m_type == PushTag || m_type == Tag, Exception, ""); return AssemblyItem(PushTag, m_data); }
+
+	AssemblyItemType type() const { return m_type; }
+	u256 const& data() const { return m_data; }
+	void setType(AssemblyItemType const _type) { m_type = _type; }
+	void setData(u256 const& _data) { m_data = _data; }
+
+	/// @returns the instruction of this item (only valid if type() == Operation)
+	Instruction instruction() const { return Instruction(byte(m_data)); }
+
+	/// @returns true if the type and data of the items are equal.
+	bool operator==(AssemblyItem const& _other) const { return m_type == _other.m_type && m_data == _other.m_data; }
+	bool operator!=(AssemblyItem const& _other) const { return !operator==(_other); }
+	/// Less-than operator compatible with operator==.
+	bool operator<(AssemblyItem const& _other) const { return std::tie(m_type, m_data) < std::tie(_other.m_type, _other.m_data); }
+
+	/// @returns an upper bound for the number of bytes required by this item, assuming that
+	/// the value of a jump tag takes @a _addressLength bytes.
+	unsigned bytesRequired(unsigned _addressLength) const;
+	int deposit() const;
+
+	bool match(AssemblyItem const& _i) const { return _i.m_type == UndefinedItem || (m_type == _i.m_type && (m_type != Operation || m_data == _i.m_data)); }
+	void setLocation(SourceLocation const& _location) { m_location = _location; }
+	SourceLocation const& location() const { return m_location; }
+
+	void setJumpType(JumpType _jumpType) { m_jumpType = _jumpType; }
+	JumpType getJumpType() const { return m_jumpType; }
+	std::string getJumpTypeAsString() const;
+
+	void setPushedValue(u256 const& _value) const { m_pushedValue = std::make_shared<u256>(_value); }
+	u256 const* pushedValue() const { return m_pushedValue.get(); }
+
+private:
+	AssemblyItemType m_type;
+	u256 m_data;
+	SourceLocation m_location;
+	JumpType m_jumpType = JumpType::Ordinary;
+	/// Pushed value for operations with data to be determined during assembly stage,
+	/// e.g. PushSubSize, PushTag, PushSub, etc.
+	mutable std::shared_ptr<u256> m_pushedValue;
+};
+
+using AssemblyItems = std::vector<AssemblyItem>;
+
+std::ostream& operator<<(std::ostream& _out, AssemblyItem const& _item);
+inline std::ostream& operator<<(std::ostream& _out, AssemblyItems const& _items)
+{
+	for (AssemblyItem const& item: _items)
+		_out << item;
+	return _out;
+}
+
+}
+}
diff --git a/libevmasm/BlockDeduplicator.cpp b/libevmasm/BlockDeduplicator.cpp
new file mode 100644
index 00000000..d930ea22
--- /dev/null
+++ b/libevmasm/BlockDeduplicator.cpp
@@ -0,0 +1,126 @@
+/*
+	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 BlockDeduplicator.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Unifies basic blocks that share content.
+ */
+
+#include <libevmasm/BlockDeduplicator.h>
+#include <functional>
+#include <libevmasm/AssemblyItem.h>
+#include <libevmasm/SemanticInformation.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+
+bool BlockDeduplicator::deduplicate()
+{
+	// Compares indices based on the suffix that starts there, ignoring tags and stopping at
+	// opcodes that stop the control flow.
+
+	// Virtual tag that signifies "the current block" and which is used to optimise loops.
+	// We abort if this virtual tag actually exists.
+	AssemblyItem pushSelf(PushTag, u256(-4));
+	if (
+		std::count(m_items.cbegin(), m_items.cend(), pushSelf.tag()) ||
+		std::count(m_items.cbegin(), m_items.cend(), pushSelf.pushTag())
+	)
+		return false;
+
+	function<bool(size_t, size_t)> comparator = [&](size_t _i, size_t _j)
+	{
+		if (_i == _j)
+			return false;
+
+		// To compare recursive loops, we have to already unify PushTag opcodes of the
+		// block's own tag.
+		AssemblyItem pushFirstTag(pushSelf);
+		AssemblyItem pushSecondTag(pushSelf);
+
+		if (_i < m_items.size() && m_items.at(_i).type() == Tag)
+			pushFirstTag = m_items.at(_i).pushTag();
+		if (_j < m_items.size() && m_items.at(_j).type() == Tag)
+			pushSecondTag = m_items.at(_j).pushTag();
+
+		BlockIterator first(m_items.begin() + _i, m_items.end(), &pushFirstTag, &pushSelf);
+		BlockIterator second(m_items.begin() + _j, m_items.end(), &pushSecondTag, &pushSelf);
+		BlockIterator end(m_items.end(), m_items.end());
+
+		if (first != end && (*first).type() == Tag)
+			++first;
+		if (second != end && (*second).type() == Tag)
+			++second;
+
+		return std::lexicographical_compare(first, end, second, end);
+	};
+
+	size_t iterations = 0;
+	for (; ; ++iterations)
+	{
+		//@todo this should probably be optimized.
+		set<size_t, function<bool(size_t, size_t)>> blocksSeen(comparator);
+		map<u256, u256> tagReplacement;
+		for (size_t i = 0; i < m_items.size(); ++i)
+		{
+			if (m_items.at(i).type() != Tag)
+				continue;
+			auto it = blocksSeen.find(i);
+			if (it == blocksSeen.end())
+				blocksSeen.insert(i);
+			else
+				tagReplacement[m_items.at(i).data()] = m_items.at(*it).data();
+		}
+
+		bool changed = false;
+		for (AssemblyItem& item: m_items)
+			if (item.type() == PushTag && tagReplacement.count(item.data()))
+			{
+				changed = true;
+				item.setData(tagReplacement.at(item.data()));
+			}
+		if (!changed)
+			break;
+	}
+	return iterations > 0;
+}
+
+BlockDeduplicator::BlockIterator& BlockDeduplicator::BlockIterator::operator++()
+{
+	if (it == end)
+		return *this;
+	if (SemanticInformation::altersControlFlow(*it) && *it != AssemblyItem(eth::Instruction::JUMPI))
+		it = end;
+	else
+	{
+		++it;
+		while (it != end && it->type() == Tag)
+			++it;
+	}
+	return *this;
+}
+
+AssemblyItem const& BlockDeduplicator::BlockIterator::operator*() const
+{
+	if (replaceItem && replaceWith && *it == *replaceItem)
+		return *replaceWith;
+	else
+		return *it;
+}
diff --git a/libevmasm/BlockDeduplicator.h b/libevmasm/BlockDeduplicator.h
new file mode 100644
index 00000000..c48835fd
--- /dev/null
+++ b/libevmasm/BlockDeduplicator.h
@@ -0,0 +1,77 @@
+/*
+	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 BlockDeduplicator.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Unifies basic blocks that share content.
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <vector>
+#include <functional>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+
+/**
+ * Optimizer class to be used to unify blocks that share content.
+ * Modifies the passed vector in place.
+ */
+class BlockDeduplicator
+{
+public:
+	BlockDeduplicator(AssemblyItems& _items): m_items(_items) {}
+	/// @returns true if something was changed
+	bool deduplicate();
+
+private:
+	/// Iterator that skips tags and skips to the end if (all branches of) the control
+	/// flow does not continue to the next instruction.
+	/// If the arguments are supplied to the constructor, replaces items on the fly.
+	struct BlockIterator: std::iterator<std::forward_iterator_tag, AssemblyItem const>
+	{
+	public:
+		BlockIterator(
+			AssemblyItems::const_iterator _it,
+			AssemblyItems::const_iterator _end,
+			AssemblyItem const* _replaceItem = nullptr,
+			AssemblyItem const* _replaceWith = nullptr
+		):
+			it(_it), end(_end), replaceItem(_replaceItem), replaceWith(_replaceWith) {}
+		BlockIterator& operator++();
+		bool operator==(BlockIterator const& _other) const { return it == _other.it; }
+		bool operator!=(BlockIterator const& _other) const { return it != _other.it; }
+		AssemblyItem const& operator*() const;
+		AssemblyItems::const_iterator it;
+		AssemblyItems::const_iterator end;
+		AssemblyItem const* replaceItem;
+		AssemblyItem const* replaceWith;
+	};
+
+	AssemblyItems& m_items;
+};
+
+}
+}
diff --git a/libevmasm/CMakeLists.txt b/libevmasm/CMakeLists.txt
new file mode 100644
index 00000000..1accb8ea
--- /dev/null
+++ b/libevmasm/CMakeLists.txt
@@ -0,0 +1,14 @@
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DSTATICLIB")
+
+aux_source_directory(. SRC_LIST)
+
+set(EXECUTABLE evmasm)
+
+file(GLOB HEADERS "*.h")
+
+add_library(${EXECUTABLE} ${SRC_LIST} ${HEADERS})
+eth_use(${EXECUTABLE} REQUIRED Eth::evmcore)
+
+install( TARGETS ${EXECUTABLE} RUNTIME DESTINATION bin ARCHIVE DESTINATION lib LIBRARY DESTINATION lib )
+install( FILES ${HEADERS} DESTINATION include/${EXECUTABLE} )
+
diff --git a/libevmasm/CommonSubexpressionEliminator.cpp b/libevmasm/CommonSubexpressionEliminator.cpp
new file mode 100644
index 00000000..0797dd29
--- /dev/null
+++ b/libevmasm/CommonSubexpressionEliminator.cpp
@@ -0,0 +1,506 @@
+/*
+	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 CommonSubexpressionEliminator.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Optimizer step for common subexpression elimination and stack reorganisation.
+ */
+
+#include <functional>
+#include <boost/range/adaptor/reversed.hpp>
+#include <libdevcore/SHA3.h>
+#include <libevmasm/CommonSubexpressionEliminator.h>
+#include <libevmasm/AssemblyItem.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+vector<AssemblyItem> CommonSubexpressionEliminator::getOptimizedItems()
+{
+	optimizeBreakingItem();
+
+	KnownState nextInitialState = m_state;
+	if (m_breakingItem)
+		nextInitialState.feedItem(*m_breakingItem);
+	KnownState nextState = nextInitialState;
+
+	ScopeGuard reset([&]()
+	{
+		m_breakingItem = nullptr;
+		m_storeOperations.clear();
+		m_initialState = move(nextInitialState);
+		m_state = move(nextState);
+	});
+
+	map<int, Id> initialStackContents;
+	map<int, Id> targetStackContents;
+	int minHeight = m_state.stackHeight() + 1;
+	if (!m_state.stackElements().empty())
+		minHeight = min(minHeight, m_state.stackElements().begin()->first);
+	for (int height = minHeight; height <= m_initialState.stackHeight(); ++height)
+		initialStackContents[height] = m_initialState.stackElement(height, SourceLocation());
+	for (int height = minHeight; height <= m_state.stackHeight(); ++height)
+		targetStackContents[height] = m_state.stackElement(height, SourceLocation());
+
+	AssemblyItems items = CSECodeGenerator(m_state.expressionClasses(), m_storeOperations).generateCode(
+		m_initialState.sequenceNumber(),
+		m_initialState.stackHeight(),
+		initialStackContents,
+		targetStackContents
+	);
+	if (m_breakingItem)
+		items.push_back(*m_breakingItem);
+
+	return items;
+}
+
+void CommonSubexpressionEliminator::feedItem(AssemblyItem const& _item, bool _copyItem)
+{
+	StoreOperation op = m_state.feedItem(_item, _copyItem);
+	if (op.isValid())
+		m_storeOperations.push_back(op);
+}
+
+void CommonSubexpressionEliminator::optimizeBreakingItem()
+{
+	if (!m_breakingItem)
+		return;
+
+	ExpressionClasses& classes = m_state.expressionClasses();
+	SourceLocation const& itemLocation = m_breakingItem->location();
+	if (*m_breakingItem == AssemblyItem(Instruction::JUMPI))
+	{
+		AssemblyItem::JumpType jumpType = m_breakingItem->getJumpType();
+
+		Id condition = m_state.stackElement(m_state.stackHeight() - 1, itemLocation);
+		if (classes.knownNonZero(condition))
+		{
+			feedItem(AssemblyItem(Instruction::SWAP1, itemLocation), true);
+			feedItem(AssemblyItem(Instruction::POP, itemLocation), true);
+
+			AssemblyItem item(Instruction::JUMP, itemLocation);
+			item.setJumpType(jumpType);
+			m_breakingItem = classes.storeItem(item);
+		}
+		else if (classes.knownZero(condition))
+		{
+			AssemblyItem it(Instruction::POP, itemLocation);
+			feedItem(it, true);
+			feedItem(it, true);
+			m_breakingItem = nullptr;
+		}
+	}
+	else if (*m_breakingItem == AssemblyItem(Instruction::RETURN))
+	{
+		Id size = m_state.stackElement(m_state.stackHeight() - 1, itemLocation);
+		if (classes.knownZero(size))
+		{
+			feedItem(AssemblyItem(Instruction::POP, itemLocation), true);
+			feedItem(AssemblyItem(Instruction::POP, itemLocation), true);
+			AssemblyItem item(Instruction::STOP, itemLocation);
+			m_breakingItem = classes.storeItem(item);
+		}
+	}
+}
+
+CSECodeGenerator::CSECodeGenerator(
+	ExpressionClasses& _expressionClasses,
+	vector<CSECodeGenerator::StoreOperation> const& _storeOperations
+):
+	m_expressionClasses(_expressionClasses)
+{
+	for (auto const& store: _storeOperations)
+		m_storeOperations[make_pair(store.target, store.slot)].push_back(store);
+}
+
+AssemblyItems CSECodeGenerator::generateCode(
+	unsigned _initialSequenceNumber,
+	int _initialStackHeight,
+	map<int, Id> const& _initialStack,
+	map<int, Id> const& _targetStackContents
+)
+{
+	m_stackHeight = _initialStackHeight;
+	m_stack = _initialStack;
+	m_targetStack = _targetStackContents;
+	for (auto const& item: m_stack)
+		m_classPositions[item.second].insert(item.first);
+
+	// generate the dependency graph starting from final storage and memory writes and target stack contents
+	for (auto const& p: m_storeOperations)
+		addDependencies(p.second.back().expression);
+	for (auto const& targetItem: m_targetStack)
+	{
+		m_finalClasses.insert(targetItem.second);
+		addDependencies(targetItem.second);
+	}
+
+	// store all needed sequenced expressions
+	set<pair<unsigned, Id>> sequencedExpressions;
+	for (auto const& p: m_neededBy)
+		for (auto id: {p.first, p.second})
+			if (unsigned seqNr = m_expressionClasses.representative(id).sequenceNumber)
+			{
+				if (seqNr < _initialSequenceNumber)
+					// Invalid sequenced operation.
+					// @todo quick fix for now. Proper fix needs to choose representative with higher
+					// sequence number during dependency analyis.
+					BOOST_THROW_EXCEPTION(StackTooDeepException());
+				sequencedExpressions.insert(make_pair(seqNr, id));
+			}
+
+	// Perform all operations on storage and memory in order, if they are needed.
+	for (auto const& seqAndId: sequencedExpressions)
+		if (!m_classPositions.count(seqAndId.second))
+			generateClassElement(seqAndId.second, true);
+
+	// generate the target stack elements
+	for (auto const& targetItem: m_targetStack)
+	{
+		if (m_stack.count(targetItem.first) && m_stack.at(targetItem.first) == targetItem.second)
+			continue; // already there
+		generateClassElement(targetItem.second);
+		assertThrow(!m_classPositions[targetItem.second].empty(), OptimizerException, "");
+		if (m_classPositions[targetItem.second].count(targetItem.first))
+			continue;
+		SourceLocation sourceLocation;
+		if (m_expressionClasses.representative(targetItem.second).item)
+			sourceLocation = m_expressionClasses.representative(targetItem.second).item->location();
+		int position = classElementPosition(targetItem.second);
+		if (position < targetItem.first)
+			// it is already at its target, we need another copy
+			appendDup(position, sourceLocation);
+		else
+			appendOrRemoveSwap(position, sourceLocation);
+		appendOrRemoveSwap(targetItem.first, sourceLocation);
+	}
+
+	// remove surplus elements
+	while (removeStackTopIfPossible())
+	{
+		// no-op
+	}
+
+	// check validity
+	int finalHeight = 0;
+	if (!m_targetStack.empty())
+		// have target stack, so its height should be the final height
+		finalHeight = (--m_targetStack.end())->first;
+	else if (!_initialStack.empty())
+		// no target stack, only erase the initial stack
+		finalHeight = _initialStack.begin()->first - 1;
+	else
+		// neither initial no target stack, no change in height
+		finalHeight = _initialStackHeight;
+	assertThrow(finalHeight == m_stackHeight, OptimizerException, "Incorrect final stack height.");
+
+	return m_generatedItems;
+}
+
+void CSECodeGenerator::addDependencies(Id _c)
+{
+	if (m_classPositions.count(_c))
+		return; // it is already on the stack
+	if (m_neededBy.count(_c))
+		return; // we already computed the dependencies for _c
+	ExpressionClasses::Expression expr = m_expressionClasses.representative(_c);
+	if (expr.item->type() == UndefinedItem)
+		BOOST_THROW_EXCEPTION(
+			// If this exception happens, we need to find a different way to generate the
+			// compound expression.
+			ItemNotAvailableException() << errinfo_comment("Undefined item requested but not available.")
+		);
+	for (Id argument: expr.arguments)
+	{
+		addDependencies(argument);
+		m_neededBy.insert(make_pair(argument, _c));
+	}
+	if (expr.item && expr.item->type() == Operation && (
+		expr.item->instruction() == Instruction::SLOAD ||
+		expr.item->instruction() == Instruction::MLOAD ||
+		expr.item->instruction() == Instruction::SHA3
+	))
+	{
+		// this loads an unknown value from storage or memory and thus, in addition to its
+		// arguments, depends on all store operations to addresses where we do not know that
+		// they are different that occur before this load
+		StoreOperation::Target target = expr.item->instruction() == Instruction::SLOAD ?
+			StoreOperation::Storage : StoreOperation::Memory;
+		Id slotToLoadFrom = expr.arguments.at(0);
+		for (auto const& p: m_storeOperations)
+		{
+			if (p.first.first != target)
+				continue;
+			Id slot = p.first.second;
+			StoreOperations const& storeOps = p.second;
+			if (storeOps.front().sequenceNumber > expr.sequenceNumber)
+				continue;
+			bool knownToBeIndependent = false;
+			switch (expr.item->instruction())
+			{
+			case Instruction::SLOAD:
+				knownToBeIndependent = m_expressionClasses.knownToBeDifferent(slot, slotToLoadFrom);
+				break;
+			case Instruction::MLOAD:
+				knownToBeIndependent = m_expressionClasses.knownToBeDifferentBy32(slot, slotToLoadFrom);
+				break;
+			case Instruction::SHA3:
+			{
+				Id length = expr.arguments.at(1);
+				AssemblyItem offsetInstr(Instruction::SUB, expr.item->location());
+				Id offsetToStart = m_expressionClasses.find(offsetInstr, {slot, slotToLoadFrom});
+				u256 const* o = m_expressionClasses.knownConstant(offsetToStart);
+				u256 const* l = m_expressionClasses.knownConstant(length);
+				if (l && *l == 0)
+					knownToBeIndependent = true;
+				else if (o)
+				{
+					// We could get problems here if both *o and *l are larger than 2**254
+					// but it is probably ok for the optimizer to produce wrong code for such cases
+					// which cannot be executed anyway because of the non-payable price.
+					if (u2s(*o) <= -32)
+						knownToBeIndependent = true;
+					else if (l && u2s(*o) >= 0 && *o >= *l)
+						knownToBeIndependent = true;
+				}
+				break;
+			}
+			default:
+				break;
+			}
+			if (knownToBeIndependent)
+				continue;
+
+			// note that store and load never have the same sequence number
+			Id latestStore = storeOps.front().expression;
+			for (auto it = ++storeOps.begin(); it != storeOps.end(); ++it)
+				if (it->sequenceNumber < expr.sequenceNumber)
+					latestStore = it->expression;
+			addDependencies(latestStore);
+			m_neededBy.insert(make_pair(latestStore, _c));
+		}
+	}
+}
+
+void CSECodeGenerator::generateClassElement(Id _c, bool _allowSequenced)
+{
+	for (auto it: m_classPositions)
+		for (auto p: it.second)
+			if (p > m_stackHeight)
+				assertThrow(false, OptimizerException, "");
+	// do some cleanup
+	removeStackTopIfPossible();
+
+	if (m_classPositions.count(_c))
+	{
+		assertThrow(
+			!m_classPositions[_c].empty(),
+			OptimizerException,
+			"Element already removed but still needed."
+		);
+		return;
+	}
+	ExpressionClasses::Expression const& expr = m_expressionClasses.representative(_c);
+	assertThrow(
+		_allowSequenced || expr.sequenceNumber == 0,
+		OptimizerException,
+		"Sequence constrained operation requested out of sequence."
+	);
+	assertThrow(expr.item, OptimizerException, "Non-generated expression without item.");
+	assertThrow(
+		expr.item->type() != UndefinedItem,
+		OptimizerException,
+		"Undefined item requested but not available."
+	);
+	vector<Id> const& arguments = expr.arguments;
+	for (Id arg: boost::adaptors::reverse(arguments))
+		generateClassElement(arg);
+
+	SourceLocation const& itemLocation = expr.item->location();
+	// The arguments are somewhere on the stack now, so it remains to move them at the correct place.
+	// This is quite difficult as sometimes, the values also have to removed in this process
+	// (if canBeRemoved() returns true) and the two arguments can be equal. For now, this is
+	// implemented for every single case for combinations of up to two arguments manually.
+	if (arguments.size() == 1)
+	{
+		if (canBeRemoved(arguments[0], _c))
+			appendOrRemoveSwap(classElementPosition(arguments[0]), itemLocation);
+		else
+			appendDup(classElementPosition(arguments[0]), itemLocation);
+	}
+	else if (arguments.size() == 2)
+	{
+		if (canBeRemoved(arguments[1], _c))
+		{
+			appendOrRemoveSwap(classElementPosition(arguments[1]), itemLocation);
+			if (arguments[0] == arguments[1])
+				appendDup(m_stackHeight, itemLocation);
+			else if (canBeRemoved(arguments[0], _c))
+			{
+				appendOrRemoveSwap(m_stackHeight - 1, itemLocation);
+				appendOrRemoveSwap(classElementPosition(arguments[0]), itemLocation);
+			}
+			else
+				appendDup(classElementPosition(arguments[0]), itemLocation);
+		}
+		else
+		{
+			if (arguments[0] == arguments[1])
+			{
+				appendDup(classElementPosition(arguments[0]), itemLocation);
+				appendDup(m_stackHeight, itemLocation);
+			}
+			else if (canBeRemoved(arguments[0], _c))
+			{
+				appendOrRemoveSwap(classElementPosition(arguments[0]), itemLocation);
+				appendDup(classElementPosition(arguments[1]), itemLocation);
+				appendOrRemoveSwap(m_stackHeight - 1, itemLocation);
+			}
+			else
+			{
+				appendDup(classElementPosition(arguments[1]), itemLocation);
+				appendDup(classElementPosition(arguments[0]), itemLocation);
+			}
+		}
+	}
+	else
+		assertThrow(
+			arguments.size() <= 2,
+			OptimizerException,
+			"Opcodes with more than two arguments not implemented yet."
+		);
+	for (size_t i = 0; i < arguments.size(); ++i)
+		assertThrow(m_stack[m_stackHeight - i] == arguments[i], OptimizerException, "Expected arguments not present." );
+
+	while (SemanticInformation::isCommutativeOperation(*expr.item) &&
+			!m_generatedItems.empty() &&
+			m_generatedItems.back() == AssemblyItem(Instruction::SWAP1))
+		// this will not append a swap but remove the one that is already there
+		appendOrRemoveSwap(m_stackHeight - 1, itemLocation);
+	for (size_t i = 0; i < arguments.size(); ++i)
+	{
+		m_classPositions[m_stack[m_stackHeight - i]].erase(m_stackHeight - i);
+		m_stack.erase(m_stackHeight - i);
+	}
+	appendItem(*expr.item);
+	if (expr.item->type() != Operation || instructionInfo(expr.item->instruction()).ret == 1)
+	{
+		m_stack[m_stackHeight] = _c;
+		m_classPositions[_c].insert(m_stackHeight);
+	}
+	else
+	{
+		assertThrow(
+			instructionInfo(expr.item->instruction()).ret == 0,
+			OptimizerException,
+			"Invalid number of return values."
+		);
+		m_classPositions[_c]; // ensure it is created to mark the expression as generated
+	}
+}
+
+int CSECodeGenerator::classElementPosition(Id _id) const
+{
+	assertThrow(
+		m_classPositions.count(_id) && !m_classPositions.at(_id).empty(),
+		OptimizerException,
+		"Element requested but is not present."
+	);
+	return *max_element(m_classPositions.at(_id).begin(), m_classPositions.at(_id).end());
+}
+
+bool CSECodeGenerator::canBeRemoved(Id _element, Id _result, int _fromPosition)
+{
+	// Default for _fromPosition is the canonical position of the element.
+	if (_fromPosition == c_invalidPosition)
+		_fromPosition = classElementPosition(_element);
+
+	bool haveCopy = m_classPositions.at(_element).size() > 1;
+	if (m_finalClasses.count(_element))
+		// It is part of the target stack. It can be removed if it is a copy that is not in the target position.
+		return haveCopy && (!m_targetStack.count(_fromPosition) || m_targetStack[_fromPosition] != _element);
+	else if (!haveCopy)
+	{
+		// Can be removed unless it is needed by a class that has not been computed yet.
+		// Note that m_classPositions also includes classes that were deleted in the meantime.
+		auto range = m_neededBy.equal_range(_element);
+		for (auto it = range.first; it != range.second; ++it)
+			if (it->second != _result && !m_classPositions.count(it->second))
+				return false;
+	}
+	return true;
+}
+
+bool CSECodeGenerator::removeStackTopIfPossible()
+{
+	if (m_stack.empty())
+		return false;
+	assertThrow(m_stack.count(m_stackHeight) > 0, OptimizerException, "");
+	Id top = m_stack[m_stackHeight];
+	if (!canBeRemoved(top, Id(-1), m_stackHeight))
+		return false;
+	m_classPositions[m_stack[m_stackHeight]].erase(m_stackHeight);
+	m_stack.erase(m_stackHeight);
+	appendItem(AssemblyItem(Instruction::POP));
+	return true;
+}
+
+void CSECodeGenerator::appendDup(int _fromPosition, SourceLocation const& _location)
+{
+	assertThrow(_fromPosition != c_invalidPosition, OptimizerException, "");
+	int instructionNum = 1 + m_stackHeight - _fromPosition;
+	assertThrow(instructionNum <= 16, StackTooDeepException, "Stack too deep, try removing local variables.");
+	assertThrow(1 <= instructionNum, OptimizerException, "Invalid stack access.");
+	appendItem(AssemblyItem(dupInstruction(instructionNum), _location));
+	m_stack[m_stackHeight] = m_stack[_fromPosition];
+	m_classPositions[m_stack[m_stackHeight]].insert(m_stackHeight);
+}
+
+void CSECodeGenerator::appendOrRemoveSwap(int _fromPosition, SourceLocation const& _location)
+{
+	assertThrow(_fromPosition != c_invalidPosition, OptimizerException, "");
+	if (_fromPosition == m_stackHeight)
+		return;
+	int instructionNum = m_stackHeight - _fromPosition;
+	assertThrow(instructionNum <= 16, StackTooDeepException, "Stack too deep, try removing local variables.");
+	assertThrow(1 <= instructionNum, OptimizerException, "Invalid stack access.");
+	appendItem(AssemblyItem(swapInstruction(instructionNum), _location));
+
+	if (m_stack[m_stackHeight] != m_stack[_fromPosition])
+	{
+		m_classPositions[m_stack[m_stackHeight]].erase(m_stackHeight);
+		m_classPositions[m_stack[m_stackHeight]].insert(_fromPosition);
+		m_classPositions[m_stack[_fromPosition]].erase(_fromPosition);
+		m_classPositions[m_stack[_fromPosition]].insert(m_stackHeight);
+		swap(m_stack[m_stackHeight], m_stack[_fromPosition]);
+	}
+	if (m_generatedItems.size() >= 2 &&
+		SemanticInformation::isSwapInstruction(m_generatedItems.back()) &&
+		*(m_generatedItems.end() - 2) == m_generatedItems.back())
+	{
+		m_generatedItems.pop_back();
+		m_generatedItems.pop_back();
+	}
+}
+
+void CSECodeGenerator::appendItem(AssemblyItem const& _item)
+{
+	m_generatedItems.push_back(_item);
+	m_stackHeight += _item.deposit();
+}
diff --git a/libevmasm/CommonSubexpressionEliminator.h b/libevmasm/CommonSubexpressionEliminator.h
new file mode 100644
index 00000000..f6c43c57
--- /dev/null
+++ b/libevmasm/CommonSubexpressionEliminator.h
@@ -0,0 +1,183 @@
+/*
+	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 CommonSubexpressionEliminator.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Optimizer step for common subexpression elimination and stack reorganisation.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <set>
+#include <tuple>
+#include <ostream>
+#include <libdevcore/CommonIO.h>
+#include <libdevcore/Exceptions.h>
+#include <libevmasm/ExpressionClasses.h>
+#include <libevmasm/SemanticInformation.h>
+#include <libevmasm/KnownState.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+
+/**
+ * Optimizer step that performs common subexpression elimination and stack reorganisation,
+ * i.e. it tries to infer equality among expressions and compute the values of two expressions
+ * known to be equal only once.
+ *
+ * The general workings are that for each assembly item that is fed into the eliminator, an
+ * equivalence class is derived from the operation and the equivalence class of its arguments.
+ * DUPi, SWAPi and some arithmetic instructions are used to infer equivalences while these
+ * classes are determined.
+ *
+ * When the list of optimized items is requested, they are generated in a bottom-up fashion,
+ * adding code for equivalence classes that were not yet computed.
+ */
+class CommonSubexpressionEliminator
+{
+public:
+	using Id = ExpressionClasses::Id;
+	using StoreOperation = KnownState::StoreOperation;
+
+	CommonSubexpressionEliminator(KnownState const& _state): m_initialState(_state), m_state(_state) {}
+
+	/// Feeds AssemblyItems into the eliminator and @returns the iterator pointing at the first
+	/// item that must be fed into a new instance of the eliminator.
+	template <class _AssemblyItemIterator>
+	_AssemblyItemIterator feedItems(_AssemblyItemIterator _iterator, _AssemblyItemIterator _end);
+
+	/// @returns the resulting items after optimization.
+	AssemblyItems getOptimizedItems();
+
+private:
+	/// Feeds the item into the system for analysis.
+	void feedItem(AssemblyItem const& _item, bool _copyItem = false);
+
+	/// Tries to optimize the item that breaks the basic block at the end.
+	void optimizeBreakingItem();
+
+	KnownState m_initialState;
+	KnownState m_state;
+	/// Keeps information about which storage or memory slots were written to at which sequence
+	/// number with what instruction.
+	std::vector<StoreOperation> m_storeOperations;
+
+	/// The item that breaks the basic block, can be nullptr.
+	/// It is usually appended to the block but can be optimized in some cases.
+	AssemblyItem const* m_breakingItem = nullptr;
+};
+
+/**
+ * Unit that generates code from current stack layout, target stack layout and information about
+ * the equivalence classes.
+ */
+class CSECodeGenerator
+{
+public:
+	using StoreOperation = CommonSubexpressionEliminator::StoreOperation;
+	using StoreOperations = std::vector<StoreOperation>;
+	using Id = ExpressionClasses::Id;
+
+	/// Initializes the code generator with the given classes and store operations.
+	/// The store operations have to be sorted by sequence number in ascending order.
+	CSECodeGenerator(ExpressionClasses& _expressionClasses, StoreOperations const& _storeOperations);
+
+	/// @returns the assembly items generated from the given requirements
+	/// @param _initialSequenceNumber starting sequence number, do not generate sequenced operations
+	/// before this number.
+	/// @param _initialStack current contents of the stack (up to stack height of zero)
+	/// @param _targetStackContents final contents of the stack, by stack height relative to initial
+	/// @note should only be called once on each object.
+	AssemblyItems generateCode(
+		unsigned _initialSequenceNumber,
+		int _initialStackHeight,
+		std::map<int, Id> const& _initialStack,
+		std::map<int, Id> const& _targetStackContents
+	);
+
+private:
+	/// Recursively discovers all dependencies to @a m_requests.
+	void addDependencies(Id _c);
+
+	/// Produce code that generates the given element if it is not yet present.
+	/// @param _allowSequenced indicates that sequence-constrained operations are allowed
+	void generateClassElement(Id _c, bool _allowSequenced = false);
+	/// @returns the position of the representative of the given id on the stack.
+	/// @note throws an exception if it is not on the stack.
+	int classElementPosition(Id _id) const;
+
+	/// @returns true if the copy of @a _element can be removed from stack position _fromPosition
+	/// - in general or, if given, while computing @a _result.
+	bool canBeRemoved(Id _element, Id _result = Id(-1), int _fromPosition = c_invalidPosition);
+
+	/// Appends code to remove the topmost stack element if it can be removed.
+	bool removeStackTopIfPossible();
+
+	/// Appends a dup instruction to m_generatedItems to retrieve the element at the given stack position.
+	void appendDup(int _fromPosition, SourceLocation const& _location);
+	/// Appends a swap instruction to m_generatedItems to retrieve the element at the given stack position.
+	/// @note this might also remove the last item if it exactly the same swap instruction.
+	void appendOrRemoveSwap(int _fromPosition, SourceLocation const& _location);
+	/// Appends the given assembly item.
+	void appendItem(AssemblyItem const& _item);
+
+	static const int c_invalidPosition = -0x7fffffff;
+
+	AssemblyItems m_generatedItems;
+	/// Current height of the stack relative to the start.
+	int m_stackHeight;
+	/// If (b, a) is in m_requests then b is needed to compute a.
+	std::multimap<Id, Id> m_neededBy;
+	/// Current content of the stack.
+	std::map<int, Id> m_stack;
+	/// Current positions of equivalence classes, equal to the empty set if already deleted.
+	std::map<Id, std::set<int>> m_classPositions;
+
+	/// The actual eqivalence class items and how to compute them.
+	ExpressionClasses& m_expressionClasses;
+	/// Keeps information about which storage or memory slots were written to by which operations.
+	/// The operations are sorted ascendingly by sequence number.
+	std::map<std::pair<StoreOperation::Target, Id>, StoreOperations> m_storeOperations;
+	/// The set of equivalence classes that should be present on the stack at the end.
+	std::set<Id> m_finalClasses;
+	std::map<int, Id> m_targetStack;
+};
+
+template <class _AssemblyItemIterator>
+_AssemblyItemIterator CommonSubexpressionEliminator::feedItems(
+	_AssemblyItemIterator _iterator,
+	_AssemblyItemIterator _end
+)
+{
+	assertThrow(!m_breakingItem, OptimizerException, "Invalid use of CommonSubexpressionEliminator.");
+	for (; _iterator != _end && !SemanticInformation::breaksCSEAnalysisBlock(*_iterator); ++_iterator)
+		feedItem(*_iterator);
+	if (_iterator != _end)
+		m_breakingItem = &(*_iterator++);
+	return _iterator;
+}
+
+}
+}
diff --git a/libevmasm/ConstantOptimiser.cpp b/libevmasm/ConstantOptimiser.cpp
new file mode 100644
index 00000000..0ebe2eab
--- /dev/null
+++ b/libevmasm/ConstantOptimiser.cpp
@@ -0,0 +1,225 @@
+/*
+	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 ConstantOptimiser.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#include "libevmasm/ConstantOptimiser.h"
+#include <libevmasm/Assembly.h>
+#include <libevmasm/GasMeter.h>
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+unsigned ConstantOptimisationMethod::optimiseConstants(
+	bool _isCreation,
+	size_t _runs,
+	Assembly& _assembly,
+	AssemblyItems& _items
+)
+{
+	unsigned optimisations = 0;
+	map<AssemblyItem, size_t> pushes;
+	for (AssemblyItem const& item: _items)
+		if (item.type() == Push)
+			pushes[item]++;
+	for (auto it: pushes)
+	{
+		AssemblyItem const& item = it.first;
+		if (item.data() < 0x100)
+			continue;
+		Params params;
+		params.multiplicity = it.second;
+		params.isCreation = _isCreation;
+		params.runs = _runs;
+		LiteralMethod lit(params, item.data());
+		bigint literalGas = lit.gasNeeded();
+		CodeCopyMethod copy(params, item.data());
+		bigint copyGas = copy.gasNeeded();
+		ComputeMethod compute(params, item.data());
+		bigint computeGas = compute.gasNeeded();
+		if (copyGas < literalGas && copyGas < computeGas)
+		{
+			copy.execute(_assembly, _items);
+			optimisations++;
+		}
+		else if (computeGas < literalGas && computeGas < copyGas)
+		{
+			compute.execute(_assembly, _items);
+			optimisations++;
+		}
+	}
+	return optimisations;
+}
+
+bigint ConstantOptimisationMethod::simpleRunGas(AssemblyItems const& _items)
+{
+	EVMSchedule schedule;	// TODO: make relevant to context.
+	bigint gas = 0;
+	for (AssemblyItem const& item: _items)
+		if (item.type() == Push)
+			gas += GasMeter::runGas(Instruction::PUSH1, schedule);
+		else if (item.type() == Operation)
+			gas += GasMeter::runGas(item.instruction(), schedule);
+	return gas;
+}
+
+bigint ConstantOptimisationMethod::dataGas(bytes const& _data) const
+{
+	if (m_params.isCreation)
+	{
+		bigint gas;
+		for (auto b: _data)
+			gas += b ? m_schedule.txDataNonZeroGas : m_schedule.txDataZeroGas;
+		return gas;
+	}
+	else
+		return m_schedule.createDataGas * dataSize();
+}
+
+size_t ConstantOptimisationMethod::bytesRequired(AssemblyItems const& _items)
+{
+	size_t size = 0;
+	for (AssemblyItem const& item: _items)
+		size += item.bytesRequired(3); // assume 3 byte addresses
+	return size;
+}
+
+void ConstantOptimisationMethod::replaceConstants(
+	AssemblyItems& _items,
+	AssemblyItems const& _replacement
+) const
+{
+	assertThrow(_items.size() > 0, OptimizerException, "");
+	for (size_t i = 0; i < _items.size(); ++i)
+	{
+		if (_items.at(i) != AssemblyItem(m_value))
+			continue;
+		_items[i] = _replacement[0];
+		_items.insert(_items.begin() + i + 1, _replacement.begin() + 1, _replacement.end());
+		i += _replacement.size() - 1;
+	}
+}
+
+bigint LiteralMethod::gasNeeded()
+{
+	return combineGas(
+		simpleRunGas({Instruction::PUSH1}),
+		// PUSHX plus data
+		(m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas) + dataGas(),
+		0
+	);
+}
+
+CodeCopyMethod::CodeCopyMethod(Params const& _params, u256 const& _value):
+	ConstantOptimisationMethod(_params, _value)
+{
+	m_copyRoutine = AssemblyItems{
+		u256(0),
+		Instruction::DUP1,
+		Instruction::MLOAD, // back up memory
+		u256(32),
+		AssemblyItem(PushData, u256(1) << 16), // has to be replaced
+		Instruction::DUP4,
+		Instruction::CODECOPY,
+		Instruction::DUP2,
+		Instruction::MLOAD,
+		Instruction::SWAP2,
+		Instruction::MSTORE
+	};
+}
+
+bigint CodeCopyMethod::gasNeeded()
+{
+	return combineGas(
+		// Run gas: we ignore memory increase costs
+		simpleRunGas(m_copyRoutine) + m_schedule.copyGas,
+		// Data gas for copy routines: Some bytes are zero, but we ignore them.
+		bytesRequired(m_copyRoutine) * (m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas),
+		// Data gas for data itself
+		dataGas(toBigEndian(m_value))
+	);
+}
+
+void CodeCopyMethod::execute(Assembly& _assembly, AssemblyItems& _items)
+{
+	bytes data = toBigEndian(m_value);
+	m_copyRoutine[4] = _assembly.newData(data);
+	replaceConstants(_items, m_copyRoutine);
+}
+
+AssemblyItems ComputeMethod::findRepresentation(u256 const& _value)
+{
+	if (_value < 0x10000)
+		// Very small value, not worth computing
+		return AssemblyItems{_value};
+	else if (dev::bytesRequired(~_value) < dev::bytesRequired(_value))
+		// Negated is shorter to represent
+		return findRepresentation(~_value) + AssemblyItems{Instruction::NOT};
+	else
+	{
+		// Decompose value into a * 2**k + b where abs(b) << 2**k
+		// Is not always better, try literal and decomposition method.
+		AssemblyItems routine{u256(_value)};
+		bigint bestGas = gasNeeded(routine);
+		for (unsigned bits = 255; bits > 8; --bits)
+		{
+			unsigned gapDetector = unsigned(_value >> (bits - 8)) & 0x1ff;
+			if (gapDetector != 0xff && gapDetector != 0x100)
+				continue;
+
+			u256 powerOfTwo = u256(1) << bits;
+			u256 upperPart = _value >> bits;
+			bigint lowerPart = _value & (powerOfTwo - 1);
+			if (abs(powerOfTwo - lowerPart) < lowerPart)
+				lowerPart = lowerPart - powerOfTwo; // make it negative
+			if (abs(lowerPart) >= (powerOfTwo >> 8))
+				continue;
+
+			AssemblyItems newRoutine;
+			if (lowerPart != 0)
+				newRoutine += findRepresentation(u256(abs(lowerPart)));
+			newRoutine += AssemblyItems{u256(bits), u256(2), Instruction::EXP};
+			if (upperPart != 1 && upperPart != 0)
+				newRoutine += findRepresentation(upperPart) + AssemblyItems{Instruction::MUL};
+			if (lowerPart > 0)
+				newRoutine += AssemblyItems{Instruction::ADD};
+			else if (lowerPart < 0)
+				newRoutine.push_back(Instruction::SUB);
+
+			bigint newGas = gasNeeded(newRoutine);
+			if (newGas < bestGas)
+			{
+				bestGas = move(newGas);
+				routine = move(newRoutine);
+			}
+		}
+		return routine;
+	}
+}
+
+bigint ComputeMethod::gasNeeded(AssemblyItems const& _routine)
+{
+	size_t numExps = count(_routine.begin(), _routine.end(), Instruction::EXP);
+	return combineGas(
+		simpleRunGas(_routine) + numExps * (m_schedule.expGas + m_schedule.expByteGas),
+		// Data gas for routine: Some bytes are zero, but we ignore them.
+		bytesRequired(_routine) * (m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas),
+		0
+	);
+}
diff --git a/libevmasm/ConstantOptimiser.h b/libevmasm/ConstantOptimiser.h
new file mode 100644
index 00000000..64cb66bb
--- /dev/null
+++ b/libevmasm/ConstantOptimiser.h
@@ -0,0 +1,155 @@
+/*
+	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 ConstantOptimiser.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#pragma once
+
+#include <vector>
+#include <libdevcore/CommonData.h>
+#include <libdevcore/CommonIO.h>
+#include <libethcore/ChainOperationParams.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+class Assembly;
+
+// TODO: FIXME: HOMESTEAD: XXX: @chfast populate m_schedule from an ExtVMFace instance via ExtVMFace::evmSchedule.
+
+/**
+ * Abstract base class for one way to change how constants are represented in the code.
+ */
+class ConstantOptimisationMethod
+{
+public:
+	/// Tries to optimised how constants are represented in the source code and modifies
+	/// @a _assembly and its @a _items.
+	/// @returns zero if no optimisations could be performed.
+	static unsigned optimiseConstants(
+		bool _isCreation,
+		size_t _runs,
+		Assembly& _assembly,
+		AssemblyItems& _items
+	);
+
+	struct Params
+	{
+		bool isCreation; ///< Whether this is called during contract creation or runtime.
+		size_t runs; ///< Estimated number of calls per opcode oven the lifetime of the contract.
+		size_t multiplicity; ///< Number of times the constant appears in the code.
+	};
+
+	explicit ConstantOptimisationMethod(Params const& _params, u256 const& _value):
+		m_params(_params), m_value(_value) {}
+	virtual bigint gasNeeded() = 0;
+	virtual void execute(Assembly& _assembly, AssemblyItems& _items) = 0;
+
+protected:
+	size_t dataSize() const { return std::max<size_t>(1, dev::bytesRequired(m_value)); }
+
+	/// @returns the run gas for the given items ignoring special gas costs
+	static bigint simpleRunGas(AssemblyItems const& _items);
+	/// @returns the gas needed to store the given data literally
+	bigint dataGas(bytes const& _data) const;
+	/// @returns the gas needed to store the value literally
+	bigint dataGas() const { return dataGas(toCompactBigEndian(m_value, 1)); }
+	static size_t bytesRequired(AssemblyItems const& _items);
+	/// @returns the combined estimated gas usage taking @a m_params into account.
+	bigint combineGas(
+		bigint const& _runGas,
+		bigint const& _repeatedDataGas,
+		bigint const& _uniqueDataGas
+	)
+	{
+		// _runGas is not multiplied by _multiplicity because the runs are "per opcode"
+		return m_params.runs * _runGas + m_params.multiplicity * _repeatedDataGas + _uniqueDataGas;
+	}
+
+	/// Replaces the constant by the code given in @a _replacement.
+	void replaceConstants(AssemblyItems& _items, AssemblyItems const& _replacement) const;
+
+	Params m_params;
+	u256 const& m_value;
+	EVMSchedule m_schedule;
+};
+
+/**
+ * Optimisation method that pushes the constant to the stack literally. This is the default method,
+ * i.e. executing it does not alter the Assembly.
+ */
+class LiteralMethod: public ConstantOptimisationMethod
+{
+public:
+	explicit LiteralMethod(Params const& _params, u256 const& _value):
+		ConstantOptimisationMethod(_params, _value) {}
+	virtual bigint gasNeeded() override;
+	virtual void execute(Assembly&, AssemblyItems&) override {}
+
+	EVMSchedule m_schedule;
+};
+
+/**
+ * Method that stores the data in the .data section of the code and copies it to the stack.
+ */
+class CodeCopyMethod: public ConstantOptimisationMethod
+{
+public:
+	explicit CodeCopyMethod(Params const& _params, u256 const& _value);
+	virtual bigint gasNeeded() override;
+	virtual void execute(Assembly& _assembly, AssemblyItems& _items) override;
+
+protected:
+	AssemblyItems m_copyRoutine;
+	EVMSchedule m_schedule;
+};
+
+/**
+ * Method that tries to compute the constant.
+ */
+class ComputeMethod: public ConstantOptimisationMethod
+{
+public:
+	explicit ComputeMethod(Params const& _params, u256 const& _value):
+		ConstantOptimisationMethod(_params, _value)
+	{
+		m_routine = findRepresentation(m_value);
+	}
+
+	virtual bigint gasNeeded() override { return gasNeeded(m_routine); }
+	virtual void execute(Assembly&, AssemblyItems& _items) override
+	{
+		replaceConstants(_items, m_routine);
+	}
+
+protected:
+	/// Tries to recursively find a way to compute @a _value.
+	AssemblyItems findRepresentation(u256 const& _value);
+	bigint gasNeeded(AssemblyItems const& _routine);
+
+	AssemblyItems m_routine;
+	EVMSchedule m_schedule;
+};
+
+}
+}
diff --git a/libevmasm/ControlFlowGraph.cpp b/libevmasm/ControlFlowGraph.cpp
new file mode 100644
index 00000000..fc2144c7
--- /dev/null
+++ b/libevmasm/ControlFlowGraph.cpp
@@ -0,0 +1,369 @@
+/*
+	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.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Control flow analysis for the optimizer.
+ */
+
+#include <libevmasm/ControlFlowGraph.h>
+#include <map>
+#include <memory>
+#include <algorithm>
+#include <libevmasm/Exceptions.h>
+#include <libevmasm/AssemblyItem.h>
+#include <libevmasm/SemanticInformation.h>
+#include <libevmasm/KnownState.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+BlockId::BlockId(u256 const& _id):
+	m_id(unsigned(_id))
+{
+	assertThrow( _id < initial().m_id, OptimizerException, "Tag number too large.");
+}
+
+BasicBlocks ControlFlowGraph::optimisedBlocks()
+{
+	if (m_items.empty())
+		return BasicBlocks();
+
+	findLargestTag();
+	splitBlocks();
+	resolveNextLinks();
+	removeUnusedBlocks();
+	setPrevLinks();
+	gatherKnowledge();
+
+	return rebuildCode();
+}
+
+void ControlFlowGraph::findLargestTag()
+{
+	m_lastUsedId = 0;
+	for (auto const& item: m_items)
+		if (item.type() == Tag || item.type() == PushTag)
+		{
+			// Assert that it can be converted.
+			BlockId(item.data());
+			m_lastUsedId = max(unsigned(item.data()), m_lastUsedId);
+		}
+}
+
+void ControlFlowGraph::splitBlocks()
+{
+	m_blocks.clear();
+	BlockId id = BlockId::initial();
+	m_blocks[id].begin = 0;
+	for (size_t index = 0; index < m_items.size(); ++index)
+	{
+		AssemblyItem const& item = m_items.at(index);
+		if (item.type() == Tag)
+		{
+			if (id)
+				m_blocks[id].end = index;
+			id = BlockId::invalid();
+		}
+		if (!id)
+		{
+			id = item.type() == Tag ? BlockId(item.data()) : generateNewId();
+			m_blocks[id].begin = index;
+		}
+		if (item.type() == PushTag)
+			m_blocks[id].pushedTags.push_back(BlockId(item.data()));
+		if (SemanticInformation::altersControlFlow(item))
+		{
+			m_blocks[id].end = index + 1;
+			if (item == Instruction::JUMP)
+				m_blocks[id].endType = BasicBlock::EndType::JUMP;
+			else if (item == Instruction::JUMPI)
+				m_blocks[id].endType = BasicBlock::EndType::JUMPI;
+			else
+				m_blocks[id].endType = BasicBlock::EndType::STOP;
+			id = BlockId::invalid();
+		}
+	}
+	if (id)
+	{
+		m_blocks[id].end = m_items.size();
+		if (m_blocks[id].endType == BasicBlock::EndType::HANDOVER)
+			m_blocks[id].endType = BasicBlock::EndType::STOP;
+	}
+}
+
+void ControlFlowGraph::resolveNextLinks()
+{
+	map<unsigned, BlockId> blockByBeginPos;
+	for (auto const& idAndBlock: m_blocks)
+		if (idAndBlock.second.begin != idAndBlock.second.end)
+			blockByBeginPos[idAndBlock.second.begin] = idAndBlock.first;
+
+	for (auto& idAndBlock: m_blocks)
+	{
+		BasicBlock& block = idAndBlock.second;
+		switch (block.endType)
+		{
+		case BasicBlock::EndType::JUMPI:
+		case BasicBlock::EndType::HANDOVER:
+			assertThrow(
+				blockByBeginPos.count(block.end),
+				OptimizerException,
+				"Successor block not found."
+			);
+			block.next = blockByBeginPos.at(block.end);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+void ControlFlowGraph::removeUnusedBlocks()
+{
+	vector<BlockId> blocksToProcess{BlockId::initial()};
+	set<BlockId> neededBlocks{BlockId::initial()};
+	while (!blocksToProcess.empty())
+	{
+		BasicBlock const& block = m_blocks.at(blocksToProcess.back());
+		blocksToProcess.pop_back();
+		for (BlockId tag: block.pushedTags)
+			if (!neededBlocks.count(tag) && m_blocks.count(tag))
+			{
+				neededBlocks.insert(tag);
+				blocksToProcess.push_back(tag);
+			}
+		if (block.next && !neededBlocks.count(block.next))
+		{
+			neededBlocks.insert(block.next);
+			blocksToProcess.push_back(block.next);
+		}
+	}
+	for (auto it = m_blocks.begin(); it != m_blocks.end();)
+		if (neededBlocks.count(it->first))
+			++it;
+		else
+			m_blocks.erase(it++);
+}
+
+void ControlFlowGraph::setPrevLinks()
+{
+	for (auto& idAndBlock: m_blocks)
+	{
+		BasicBlock& block = idAndBlock.second;
+		switch (block.endType)
+		{
+		case BasicBlock::EndType::JUMPI:
+		case BasicBlock::EndType::HANDOVER:
+			assertThrow(
+				!m_blocks.at(block.next).prev,
+				OptimizerException,
+				"Successor already has predecessor."
+			);
+			m_blocks[block.next].prev = idAndBlock.first;
+			break;
+		default:
+			break;
+		}
+	}
+	// If block ends with jump to not yet linked block, link them removing the jump
+	for (auto& idAndBlock: m_blocks)
+	{
+		BlockId blockId = idAndBlock.first;
+		BasicBlock& block = idAndBlock.second;
+		if (block.endType != BasicBlock::EndType::JUMP || block.end - block.begin < 2)
+			continue;
+		AssemblyItem const& push = m_items.at(block.end - 2);
+		if (push.type() != PushTag)
+			continue;
+		BlockId nextId(push.data());
+		if (m_blocks.count(nextId) && m_blocks.at(nextId).prev)
+			continue;
+		bool hasLoop = false;
+		for (BlockId id = nextId; id && m_blocks.count(id) && !hasLoop; id = m_blocks.at(id).next)
+			hasLoop = (id == blockId);
+		if (hasLoop || !m_blocks.count(nextId))
+			continue;
+
+		m_blocks[nextId].prev = blockId;
+		block.next = nextId;
+		block.end -= 2;
+		assertThrow(
+			!block.pushedTags.empty() && block.pushedTags.back() == nextId,
+			OptimizerException,
+			"Last pushed tag not at end of pushed list."
+		);
+		block.pushedTags.pop_back();
+		block.endType = BasicBlock::EndType::HANDOVER;
+	}
+}
+
+void ControlFlowGraph::gatherKnowledge()
+{
+	// @todo actually we know that memory is filled with zeros at the beginning,
+	// we could make use of that.
+	KnownStatePointer emptyState = make_shared<KnownState>();
+	bool unknownJumpEncountered = false;
+
+	struct WorkQueueItem {
+		BlockId blockId;
+		KnownStatePointer state;
+		set<BlockId> blocksSeen;
+	};
+
+	vector<WorkQueueItem> workQueue{WorkQueueItem{BlockId::initial(), emptyState->copy(), set<BlockId>()}};
+	auto addWorkQueueItem = [&](WorkQueueItem const& _currentItem, BlockId _to, KnownStatePointer const& _state)
+	{
+		WorkQueueItem item;
+		item.blockId = _to;
+		item.state = _state->copy();
+		item.blocksSeen = _currentItem.blocksSeen;
+		item.blocksSeen.insert(_currentItem.blockId);
+		workQueue.push_back(move(item));
+	};
+
+	while (!workQueue.empty())
+	{
+		WorkQueueItem item = move(workQueue.back());
+		workQueue.pop_back();
+		//@todo we might have to do something like incrementing the sequence number for each JUMPDEST
+		assertThrow(!!item.blockId, OptimizerException, "");
+		if (!m_blocks.count(item.blockId))
+			continue; // too bad, we do not know the tag, probably an invalid jump
+		BasicBlock& block = m_blocks.at(item.blockId);
+		KnownStatePointer state = item.state;
+		if (block.startState)
+		{
+			state->reduceToCommonKnowledge(*block.startState, !item.blocksSeen.count(item.blockId));
+			if (*state == *block.startState)
+				continue;
+		}
+
+		block.startState = state->copy();
+
+		// Feed all items except for the final jump yet because it will erase the target tag.
+		unsigned pc = block.begin;
+		while (pc < block.end && !SemanticInformation::altersControlFlow(m_items.at(pc)))
+			state->feedItem(m_items.at(pc++));
+
+		if (
+			block.endType == BasicBlock::EndType::JUMP ||
+			block.endType == BasicBlock::EndType::JUMPI
+		)
+		{
+			assertThrow(block.begin <= pc && pc == block.end - 1, OptimizerException, "");
+			//@todo in the case of JUMPI, add knowledge about the condition to the state
+			// (for both values of the condition)
+			set<u256> tags = state->tagsInExpression(
+				state->stackElement(state->stackHeight(), SourceLocation())
+			);
+			state->feedItem(m_items.at(pc++));
+
+			if (tags.empty())
+			{
+				if (!unknownJumpEncountered)
+				{
+					// We do not know the target of this jump, so we have to reset the states of all
+					// JUMPDESTs.
+					unknownJumpEncountered = true;
+					for (auto const& it: m_blocks)
+						if (it.second.begin < it.second.end && m_items[it.second.begin].type() == Tag)
+							workQueue.push_back(WorkQueueItem{it.first, emptyState->copy(), set<BlockId>()});
+				}
+			}
+			else
+				for (auto tag: tags)
+					addWorkQueueItem(item, BlockId(tag), state);
+		}
+		else if (block.begin <= pc && pc < block.end)
+			state->feedItem(m_items.at(pc++));
+		assertThrow(block.end <= block.begin || pc == block.end, OptimizerException, "");
+
+		block.endState = state;
+
+		if (
+			block.endType == BasicBlock::EndType::HANDOVER ||
+			block.endType == BasicBlock::EndType::JUMPI
+		)
+			addWorkQueueItem(item, block.next, state);
+	}
+
+	// Remove all blocks we never visited here. This might happen because a tag is pushed but
+	// never used for a JUMP.
+	// Note that this invalidates some contents of pushedTags
+	for (auto it = m_blocks.begin(); it != m_blocks.end();)
+		if (!it->second.startState)
+			it = m_blocks.erase(it);
+		else
+			it++;
+}
+
+BasicBlocks ControlFlowGraph::rebuildCode()
+{
+	map<BlockId, unsigned> pushes;
+	for (auto& idAndBlock: m_blocks)
+		for (BlockId ref: idAndBlock.second.pushedTags)
+			if (m_blocks.count(ref))
+				pushes[ref]++;
+
+	set<BlockId> blocksToAdd;
+	for (auto it: m_blocks)
+		blocksToAdd.insert(it.first);
+	set<BlockId> blocksAdded;
+	BasicBlocks blocks;
+
+	for (
+		BlockId blockId = BlockId::initial();
+		blockId;
+		blockId = blocksToAdd.empty() ? BlockId::invalid() : *blocksToAdd.begin()
+	)
+	{
+		bool previousHandedOver = (blockId == BlockId::initial());
+		while (m_blocks.at(blockId).prev)
+			blockId = m_blocks.at(blockId).prev;
+		for (; blockId; blockId = m_blocks.at(blockId).next)
+		{
+			BasicBlock& block = m_blocks.at(blockId);
+			blocksToAdd.erase(blockId);
+			blocksAdded.insert(blockId);
+
+			if (block.begin == block.end)
+				continue;
+			// If block starts with unused tag, skip it.
+			if (previousHandedOver && !pushes[blockId] && m_items[block.begin].type() == Tag)
+				++block.begin;
+			if (block.begin < block.end)
+			{
+				blocks.push_back(block);
+				blocks.back().startState->clearTagUnions();
+				blocks.back().endState->clearTagUnions();
+			}
+			previousHandedOver = (block.endType == BasicBlock::EndType::HANDOVER);
+		}
+	}
+
+	return blocks;
+}
+
+BlockId ControlFlowGraph::generateNewId()
+{
+	BlockId id = BlockId(++m_lastUsedId);
+	assertThrow(id < BlockId::initial(), OptimizerException, "Out of block IDs.");
+	return id;
+}
diff --git a/libevmasm/ControlFlowGraph.h b/libevmasm/ControlFlowGraph.h
new file mode 100644
index 00000000..4480ba49
--- /dev/null
+++ b/libevmasm/ControlFlowGraph.h
@@ -0,0 +1,120 @@
+/*
+	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>;
+
+class ControlFlowGraph
+{
+public:
+	/// Initializes the control flow graph.
+	/// @a _items has to persist across the usage of this class.
+	ControlFlowGraph(AssemblyItems const& _items): m_items(_items) {}
+	/// @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;
+	std::map<BlockId, BasicBlock> m_blocks;
+};
+
+
+}
+}
diff --git a/libevmasm/Exceptions.h b/libevmasm/Exceptions.h
new file mode 100644
index 00000000..03b8afde
--- /dev/null
+++ b/libevmasm/Exceptions.h
@@ -0,0 +1,37 @@
+/*
+	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 Exceptions.h
+ * @author Christian <c@ethdev.com>
+ * @date 2014
+ */
+
+#pragma once
+
+#include <libdevcore/Exceptions.h>
+
+namespace dev
+{
+namespace eth
+{
+
+struct AssemblyException: virtual Exception {};
+struct OptimizerException: virtual AssemblyException {};
+struct StackTooDeepException: virtual OptimizerException {};
+struct ItemNotAvailableException: virtual OptimizerException {};
+
+}
+}
diff --git a/libevmasm/ExpressionClasses.cpp b/libevmasm/ExpressionClasses.cpp
new file mode 100644
index 00000000..9d13a57a
--- /dev/null
+++ b/libevmasm/ExpressionClasses.cpp
@@ -0,0 +1,511 @@
+/*
+	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 ExpressionClasses.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Container for equivalence classes of expressions for use in common subexpression elimination.
+ */
+
+#include <libevmasm/ExpressionClasses.h>
+#include <utility>
+#include <tuple>
+#include <functional>
+#include <boost/range/adaptor/reversed.hpp>
+#include <boost/noncopyable.hpp>
+#include <libevmasm/Assembly.h>
+#include <libevmasm/CommonSubexpressionEliminator.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+
+bool ExpressionClasses::Expression::operator<(ExpressionClasses::Expression const& _other) const
+{
+	assertThrow(!!item && !!_other.item, OptimizerException, "");
+	auto type = item->type();
+	auto otherType = _other.item->type();
+	return std::tie(type, item->data(), arguments, sequenceNumber) <
+		std::tie(otherType, _other.item->data(), _other.arguments, _other.sequenceNumber);
+}
+
+ExpressionClasses::Id ExpressionClasses::find(
+	AssemblyItem const& _item,
+	Ids const& _arguments,
+	bool _copyItem,
+	unsigned _sequenceNumber
+)
+{
+	Expression exp;
+	exp.id = Id(-1);
+	exp.item = &_item;
+	exp.arguments = _arguments;
+	exp.sequenceNumber = _sequenceNumber;
+
+	if (SemanticInformation::isCommutativeOperation(_item))
+		sort(exp.arguments.begin(), exp.arguments.end());
+
+	if (SemanticInformation::isDeterministic(_item))
+	{
+		auto it = m_expressions.find(exp);
+		if (it != m_expressions.end())
+			return it->id;
+	}
+
+	if (_copyItem)
+		exp.item = storeItem(_item);
+
+	ExpressionClasses::Id id = tryToSimplify(exp);
+	if (id < m_representatives.size())
+		exp.id = id;
+	else
+	{
+		exp.id = m_representatives.size();
+		m_representatives.push_back(exp);
+	}
+	m_expressions.insert(exp);
+	return exp.id;
+}
+
+void ExpressionClasses::forceEqual(
+	ExpressionClasses::Id _id,
+	AssemblyItem const& _item,
+	ExpressionClasses::Ids const& _arguments,
+	bool _copyItem
+)
+{
+	Expression exp;
+	exp.id = _id;
+	exp.item = &_item;
+	exp.arguments = _arguments;
+
+	if (SemanticInformation::isCommutativeOperation(_item))
+		sort(exp.arguments.begin(), exp.arguments.end());
+
+	if (_copyItem)
+		exp.item = storeItem(_item);
+
+	m_expressions.insert(exp);
+}
+
+ExpressionClasses::Id ExpressionClasses::newClass(SourceLocation const& _location)
+{
+	Expression exp;
+	exp.id = m_representatives.size();
+	exp.item = storeItem(AssemblyItem(UndefinedItem, (u256(1) << 255) + exp.id, _location));
+	m_representatives.push_back(exp);
+	m_expressions.insert(exp);
+	return exp.id;
+}
+
+bool ExpressionClasses::knownToBeDifferent(ExpressionClasses::Id _a, ExpressionClasses::Id _b)
+{
+	// Try to simplify "_a - _b" and return true iff the value is a non-zero constant.
+	return knownNonZero(find(Instruction::SUB, {_a, _b}));
+}
+
+bool ExpressionClasses::knownToBeDifferentBy32(ExpressionClasses::Id _a, ExpressionClasses::Id _b)
+{
+	// Try to simplify "_a - _b" and return true iff the value is at least 32 away from zero.
+	u256 const* v = knownConstant(find(Instruction::SUB, {_a, _b}));
+	// forbidden interval is ["-31", 31]
+	return v && *v + 31 > u256(62);
+}
+
+bool ExpressionClasses::knownZero(Id _c)
+{
+	return Pattern(u256(0)).matches(representative(_c), *this);
+}
+
+bool ExpressionClasses::knownNonZero(Id _c)
+{
+	return Pattern(u256(0)).matches(representative(find(Instruction::ISZERO, {_c})), *this);
+}
+
+u256 const* ExpressionClasses::knownConstant(Id _c)
+{
+	map<unsigned, Expression const*> matchGroups;
+	Pattern constant(Push);
+	constant.setMatchGroup(1, matchGroups);
+	if (!constant.matches(representative(_c), *this))
+		return nullptr;
+	return &constant.d();
+}
+
+AssemblyItem const* ExpressionClasses::storeItem(AssemblyItem const& _item)
+{
+	m_spareAssemblyItems.push_back(make_shared<AssemblyItem>(_item));
+	return m_spareAssemblyItems.back().get();
+}
+
+string ExpressionClasses::fullDAGToString(ExpressionClasses::Id _id) const
+{
+	Expression const& expr = representative(_id);
+	stringstream str;
+	str << dec << expr.id << ":";
+	if (expr.item)
+	{
+		str << *expr.item << "(";
+		for (Id arg: expr.arguments)
+			str << fullDAGToString(arg) << ",";
+		str << ")";
+	}
+	else
+		str << " UNIQUE";
+	return str.str();
+}
+
+class Rules: public boost::noncopyable
+{
+public:
+	Rules();
+	void resetMatchGroups() { m_matchGroups.clear(); }
+	vector<pair<Pattern, function<Pattern()>>> rules() const { return m_rules; }
+
+private:
+	using Expression = ExpressionClasses::Expression;
+	map<unsigned, Expression const*> m_matchGroups;
+	vector<pair<Pattern, function<Pattern()>>> m_rules;
+};
+
+template <class S> S divWorkaround(S const& _a, S const& _b)
+{
+	return (S)(bigint(_a) / bigint(_b));
+}
+
+template <class S> S modWorkaround(S const& _a, S const& _b)
+{
+	return (S)(bigint(_a) % bigint(_b));
+}
+
+Rules::Rules()
+{
+	// Multiple occurences of one of these inside one rule must match the same equivalence class.
+	// Constants.
+	Pattern A(Push);
+	Pattern B(Push);
+	Pattern C(Push);
+	// Anything.
+	Pattern X;
+	Pattern Y;
+	Pattern Z;
+	A.setMatchGroup(1, m_matchGroups);
+	B.setMatchGroup(2, m_matchGroups);
+	C.setMatchGroup(3, m_matchGroups);
+	X.setMatchGroup(4, m_matchGroups);
+	Y.setMatchGroup(5, m_matchGroups);
+	Z.setMatchGroup(6, m_matchGroups);
+
+	m_rules = vector<pair<Pattern, function<Pattern()>>>{
+		// arithmetics on constants
+		{{Instruction::ADD, {A, B}}, [=]{ return A.d() + B.d(); }},
+		{{Instruction::MUL, {A, B}}, [=]{ return A.d() * B.d(); }},
+		{{Instruction::SUB, {A, B}}, [=]{ return A.d() - B.d(); }},
+		{{Instruction::DIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : divWorkaround(A.d(), B.d()); }},
+		{{Instruction::SDIV, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(divWorkaround(u2s(A.d()), u2s(B.d()))); }},
+		{{Instruction::MOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : modWorkaround(A.d(), B.d()); }},
+		{{Instruction::SMOD, {A, B}}, [=]{ return B.d() == 0 ? 0 : s2u(modWorkaround(u2s(A.d()), u2s(B.d()))); }},
+		{{Instruction::EXP, {A, B}}, [=]{ return u256(boost::multiprecision::powm(bigint(A.d()), bigint(B.d()), bigint(1) << 256)); }},
+		{{Instruction::NOT, {A}}, [=]{ return ~A.d(); }},
+		{{Instruction::LT, {A, B}}, [=]() { return A.d() < B.d() ? u256(1) : 0; }},
+		{{Instruction::GT, {A, B}}, [=]() -> u256 { return A.d() > B.d() ? 1 : 0; }},
+		{{Instruction::SLT, {A, B}}, [=]() -> u256 { return u2s(A.d()) < u2s(B.d()) ? 1 : 0; }},
+		{{Instruction::SGT, {A, B}}, [=]() -> u256 { return u2s(A.d()) > u2s(B.d()) ? 1 : 0; }},
+		{{Instruction::EQ, {A, B}}, [=]() -> u256 { return A.d() == B.d() ? 1 : 0; }},
+		{{Instruction::ISZERO, {A}}, [=]() -> u256 { return A.d() == 0 ? 1 : 0; }},
+		{{Instruction::AND, {A, B}}, [=]{ return A.d() & B.d(); }},
+		{{Instruction::OR, {A, B}}, [=]{ return A.d() | B.d(); }},
+		{{Instruction::XOR, {A, B}}, [=]{ return A.d() ^ B.d(); }},
+		{{Instruction::BYTE, {A, B}}, [=]{ return A.d() >= 32 ? 0 : (B.d() >> unsigned(8 * (31 - A.d()))) & 0xff; }},
+		{{Instruction::ADDMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) + bigint(B.d())) % C.d()); }},
+		{{Instruction::MULMOD, {A, B, C}}, [=]{ return C.d() == 0 ? 0 : u256((bigint(A.d()) * bigint(B.d())) % C.d()); }},
+		{{Instruction::MULMOD, {A, B, C}}, [=]{ return A.d() * B.d(); }},
+		{{Instruction::SIGNEXTEND, {A, B}}, [=]() -> u256 {
+			if (A.d() >= 31)
+				return B.d();
+			unsigned testBit = unsigned(A.d()) * 8 + 7;
+			u256 mask = (u256(1) << testBit) - 1;
+			return u256(boost::multiprecision::bit_test(B.d(), testBit) ? B.d() | ~mask : B.d() & mask);
+		}},
+
+		// invariants involving known constants
+		{{Instruction::ADD, {X, 0}}, [=]{ return X; }},
+		{{Instruction::MUL, {X, 1}}, [=]{ return X; }},
+		{{Instruction::DIV, {X, 1}}, [=]{ return X; }},
+		{{Instruction::SDIV, {X, 1}}, [=]{ return X; }},
+		{{Instruction::OR, {X, 0}}, [=]{ return X; }},
+		{{Instruction::XOR, {X, 0}}, [=]{ return X; }},
+		{{Instruction::AND, {X, ~u256(0)}}, [=]{ return X; }},
+		{{Instruction::MUL, {X, 0}}, [=]{ return u256(0); }},
+		{{Instruction::DIV, {X, 0}}, [=]{ return u256(0); }},
+		{{Instruction::MOD, {X, 0}}, [=]{ return u256(0); }},
+		{{Instruction::MOD, {0, X}}, [=]{ return u256(0); }},
+		{{Instruction::AND, {X, 0}}, [=]{ return u256(0); }},
+		{{Instruction::OR, {X, ~u256(0)}}, [=]{ return ~u256(0); }},
+		// operations involving an expression and itself
+		{{Instruction::AND, {X, X}}, [=]{ return X; }},
+		{{Instruction::OR, {X, X}}, [=]{ return X; }},
+		{{Instruction::SUB, {X, X}}, [=]{ return u256(0); }},
+		{{Instruction::EQ, {X, X}}, [=]{ return u256(1); }},
+		{{Instruction::LT, {X, X}}, [=]{ return u256(0); }},
+		{{Instruction::SLT, {X, X}}, [=]{ return u256(0); }},
+		{{Instruction::GT, {X, X}}, [=]{ return u256(0); }},
+		{{Instruction::SGT, {X, X}}, [=]{ return u256(0); }},
+		{{Instruction::MOD, {X, X}}, [=]{ return u256(0); }},
+
+		{{Instruction::NOT, {{Instruction::NOT, {X}}}}, [=]{ return X; }},
+	};
+	// Double negation of opcodes with binary result
+	for (auto const& op: vector<Instruction>{
+		Instruction::EQ,
+		Instruction::LT,
+		Instruction::SLT,
+		Instruction::GT,
+		Instruction::SGT
+	})
+		m_rules.push_back({
+			{Instruction::ISZERO, {{Instruction::ISZERO, {{op, {X, Y}}}}}},
+			[=]() -> Pattern { return {op, {X, Y}}; }
+		});
+	m_rules.push_back({
+		{Instruction::ISZERO, {{Instruction::ISZERO, {{Instruction::ISZERO, {X}}}}}},
+		[=]() -> Pattern { return {Instruction::ISZERO, {X}}; }
+	});
+	// Associative operations
+	for (auto const& opFun: vector<pair<Instruction,function<u256(u256 const&,u256 const&)>>>{
+		{Instruction::ADD, plus<u256>()},
+		{Instruction::MUL, multiplies<u256>()},
+		{Instruction::AND, bit_and<u256>()},
+		{Instruction::OR, bit_or<u256>()},
+		{Instruction::XOR, bit_xor<u256>()}
+	})
+	{
+		auto op = opFun.first;
+		auto fun = opFun.second;
+		// Moving constants to the outside, order matters here!
+		// we need actions that return expressions (or patterns?) here, and we need also reversed rules
+		// (X+A)+B -> X+(A+B)
+		m_rules += vector<pair<Pattern, function<Pattern()>>>{{
+			{op, {{op, {X, A}}, B}},
+			[=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
+		}, {
+		// X+(Y+A) -> (X+Y)+A
+			{op, {{op, {X, A}}, Y}},
+			[=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
+		}, {
+		// For now, we still need explicit commutativity for the inner pattern
+			{op, {{op, {A, X}}, B}},
+			[=]() -> Pattern { return {op, {X, fun(A.d(), B.d())}}; }
+		}, {
+			{op, {{op, {A, X}}, Y}},
+			[=]() -> Pattern { return {op, {{op, {X, Y}}, A}}; }
+		}};
+	}
+	// move constants across subtractions
+	m_rules += vector<pair<Pattern, function<Pattern()>>>{
+		{
+			// X - A -> X + (-A)
+			{Instruction::SUB, {X, A}},
+			[=]() -> Pattern { return {Instruction::ADD, {X, 0 - A.d()}}; }
+		}, {
+			// (X + A) - Y -> (X - Y) + A
+			{Instruction::SUB, {{Instruction::ADD, {X, A}}, Y}},
+			[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
+		}, {
+			// (A + X) - Y -> (X - Y) + A
+			{Instruction::SUB, {{Instruction::ADD, {A, X}}, Y}},
+			[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, A}}; }
+		}, {
+			// X - (Y + A) -> (X - Y) + (-A)
+			{Instruction::SUB, {X, {Instruction::ADD, {Y, A}}}},
+			[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
+		}, {
+			// X - (A + Y) -> (X - Y) + (-A)
+			{Instruction::SUB, {X, {Instruction::ADD, {A, Y}}}},
+			[=]() -> Pattern { return {Instruction::ADD, {{Instruction::SUB, {X, Y}}, 0 - A.d()}}; }
+		}
+	};
+}
+
+ExpressionClasses::Id ExpressionClasses::tryToSimplify(Expression const& _expr, bool _secondRun)
+{
+	static Rules rules;
+
+	if (
+		!_expr.item ||
+		_expr.item->type() != Operation ||
+		!SemanticInformation::isDeterministic(*_expr.item)
+	)
+		return -1;
+
+	for (auto const& rule: rules.rules())
+	{
+		rules.resetMatchGroups();
+		if (rule.first.matches(_expr, *this))
+		{
+			// Debug info
+			//cout << "Simplifying " << *_expr.item << "(";
+			//for (Id arg: _expr.arguments)
+			//	cout << fullDAGToString(arg) << ", ";
+			//cout << ")" << endl;
+			//cout << "with rule " << rule.first.toString() << endl;
+			//ExpressionTemplate t(rule.second());
+			//cout << "to " << rule.second().toString() << endl;
+			return rebuildExpression(ExpressionTemplate(rule.second(), _expr.item->location()));
+		}
+	}
+
+	if (!_secondRun && _expr.arguments.size() == 2 && SemanticInformation::isCommutativeOperation(*_expr.item))
+	{
+		Expression expr = _expr;
+		swap(expr.arguments[0], expr.arguments[1]);
+		return tryToSimplify(expr, true);
+	}
+
+	return -1;
+}
+
+ExpressionClasses::Id ExpressionClasses::rebuildExpression(ExpressionTemplate const& _template)
+{
+	if (_template.hasId)
+		return _template.id;
+
+	Ids arguments;
+	for (ExpressionTemplate const& t: _template.arguments)
+		arguments.push_back(rebuildExpression(t));
+	return find(_template.item, arguments);
+}
+
+
+Pattern::Pattern(Instruction _instruction, std::vector<Pattern> const& _arguments):
+	m_type(Operation),
+	m_requireDataMatch(true),
+	m_data(_instruction),
+	m_arguments(_arguments)
+{
+}
+
+void Pattern::setMatchGroup(unsigned _group, map<unsigned, Expression const*>& _matchGroups)
+{
+	m_matchGroup = _group;
+	m_matchGroups = &_matchGroups;
+}
+
+bool Pattern::matches(Expression const& _expr, ExpressionClasses const& _classes) const
+{
+	if (!matchesBaseItem(_expr.item))
+		return false;
+	if (m_matchGroup)
+	{
+		if (!m_matchGroups->count(m_matchGroup))
+			(*m_matchGroups)[m_matchGroup] = &_expr;
+		else if ((*m_matchGroups)[m_matchGroup]->id != _expr.id)
+			return false;
+	}
+	assertThrow(m_arguments.size() == 0 || _expr.arguments.size() == m_arguments.size(), OptimizerException, "");
+	for (size_t i = 0; i < m_arguments.size(); ++i)
+		if (!m_arguments[i].matches(_classes.representative(_expr.arguments[i]), _classes))
+			return false;
+	return true;
+}
+
+AssemblyItem Pattern::toAssemblyItem(SourceLocation const& _location) const
+{
+	return AssemblyItem(m_type, m_data, _location);
+}
+
+string Pattern::toString() const
+{
+	stringstream s;
+	switch (m_type)
+	{
+	case Operation:
+		s << instructionInfo(Instruction(unsigned(m_data))).name;
+		break;
+	case Push:
+		s << "PUSH " << hex << m_data;
+		break;
+	case UndefinedItem:
+		s << "ANY";
+		break;
+	default:
+		s << "t=" << dec << m_type << " d=" << hex << m_data;
+		break;
+	}
+	if (!m_requireDataMatch)
+		s << " ~";
+	if (m_matchGroup)
+		s << "[" << dec << m_matchGroup << "]";
+	s << "(";
+	for (Pattern const& p: m_arguments)
+		s << p.toString() << ", ";
+	s << ")";
+	return s.str();
+}
+
+bool Pattern::matchesBaseItem(AssemblyItem const* _item) const
+{
+	if (m_type == UndefinedItem)
+		return true;
+	if (!_item)
+		return false;
+	if (m_type != _item->type())
+		return false;
+	if (m_requireDataMatch && m_data != _item->data())
+		return false;
+	return true;
+}
+
+Pattern::Expression const& Pattern::matchGroupValue() const
+{
+	assertThrow(m_matchGroup > 0, OptimizerException, "");
+	assertThrow(!!m_matchGroups, OptimizerException, "");
+	assertThrow((*m_matchGroups)[m_matchGroup], OptimizerException, "");
+	return *(*m_matchGroups)[m_matchGroup];
+}
+
+
+ExpressionTemplate::ExpressionTemplate(Pattern const& _pattern, SourceLocation const& _location)
+{
+	if (_pattern.matchGroup())
+	{
+		hasId = true;
+		id = _pattern.id();
+	}
+	else
+	{
+		hasId = false;
+		item = _pattern.toAssemblyItem(_location);
+	}
+	for (auto const& arg: _pattern.arguments())
+		arguments.push_back(ExpressionTemplate(arg, _location));
+}
+
+string ExpressionTemplate::toString() const
+{
+	stringstream s;
+	if (hasId)
+		s << id;
+	else
+		s << item;
+	s << "(";
+	for (auto const& arg: arguments)
+		s << arg.toString();
+	s << ")";
+	return s.str();
+}
diff --git a/libevmasm/ExpressionClasses.h b/libevmasm/ExpressionClasses.h
new file mode 100644
index 00000000..4bfd7d24
--- /dev/null
+++ b/libevmasm/ExpressionClasses.h
@@ -0,0 +1,190 @@
+/*
+	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 ExpressionClasses.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Container for equivalence classes of expressions for use in common subexpression elimination.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <memory>
+#include <libdevcore/Common.h>
+#include <libevmasm/AssemblyItem.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class Pattern;
+struct ExpressionTemplate;
+
+/**
+ * Collection of classes of equivalent expressions that can also determine the class of an expression.
+ * Identifiers are contiguously assigned to new classes starting from zero.
+ */
+class ExpressionClasses
+{
+public:
+	using Id = unsigned;
+	using Ids = std::vector<Id>;
+
+	struct Expression
+	{
+		Id id;
+		AssemblyItem const* item = nullptr;
+		Ids arguments;
+		/// Storage modification sequence, only used for storage and memory operations.
+		unsigned sequenceNumber = 0;
+		/// Behaves as if this was a tuple of (item->type(), item->data(), arguments, sequenceNumber).
+		bool operator<(Expression const& _other) const;
+	};
+
+	/// Retrieves the id of the expression equivalence class resulting from the given item applied to the
+	/// given classes, might also create a new one.
+	/// @param _copyItem if true, copies the assembly item to an internal storage instead of just
+	/// keeping a pointer.
+	/// The @a _sequenceNumber indicates the current storage or memory access sequence.
+	Id find(
+		AssemblyItem const& _item,
+		Ids const& _arguments = {},
+		bool _copyItem = true,
+		unsigned _sequenceNumber = 0
+	);
+	/// @returns the canonical representative of an expression class.
+	Expression const& representative(Id _id) const { return m_representatives.at(_id); }
+	/// @returns the number of classes.
+	Id size() const { return m_representatives.size(); }
+
+	/// Forces the given @a _item with @a _arguments to the class @a _id. This can be used to
+	/// add prior knowledge e.g. about CALLDATA, but has to be used with caution. Will not work as
+	/// expected if @a _item applied to @a _arguments already exists.
+	void forceEqual(Id _id, AssemblyItem const& _item, Ids const& _arguments, bool _copyItem = true);
+
+	/// @returns the id of a new class which is different to all other classes.
+	Id newClass(SourceLocation const& _location);
+
+	/// @returns true if the values of the given classes are known to be different (on every input).
+	/// @note that this function might still return false for some different inputs.
+	bool knownToBeDifferent(Id _a, Id _b);
+	/// Similar to @a knownToBeDifferent but require that abs(_a - b) >= 32.
+	bool knownToBeDifferentBy32(Id _a, Id _b);
+	/// @returns true if the value of the given class is known to be zero.
+	/// @note that this is not the negation of knownNonZero
+	bool knownZero(Id _c);
+	/// @returns true if the value of the given class is known to be nonzero.
+	/// @note that this is not the negation of knownZero
+	bool knownNonZero(Id _c);
+	/// @returns a pointer to the value if the given class is known to be a constant,
+	/// and a nullptr otherwise.
+	u256 const* knownConstant(Id _c);
+
+	/// Stores a copy of the given AssemblyItem and returns a pointer to the copy that is valid for
+	/// the lifetime of the ExpressionClasses object.
+	AssemblyItem const* storeItem(AssemblyItem const& _item);
+
+	std::string fullDAGToString(Id _id) const;
+
+private:
+	/// Tries to simplify the given expression.
+	/// @returns its class if it possible or Id(-1) otherwise.
+	/// @param _secondRun is set to true for the second run where arguments of commutative expressions are reversed
+	Id tryToSimplify(Expression const& _expr, bool _secondRun = false);
+
+	/// Rebuilds an expression from a (matched) pattern.
+	Id rebuildExpression(ExpressionTemplate const& _template);
+
+	std::vector<std::pair<Pattern, std::function<Pattern()>>> createRules() const;
+
+	/// Expression equivalence class representatives - we only store one item of an equivalence.
+	std::vector<Expression> m_representatives;
+	/// All expression ever encountered.
+	std::set<Expression> m_expressions;
+	std::vector<std::shared_ptr<AssemblyItem>> m_spareAssemblyItems;
+};
+
+/**
+ * Pattern to match against an expression.
+ * Also stores matched expressions to retrieve them later, for constructing new expressions using
+ * ExpressionTemplate.
+ */
+class Pattern
+{
+public:
+	using Expression = ExpressionClasses::Expression;
+	using Id = ExpressionClasses::Id;
+
+	// Matches a specific constant value.
+	Pattern(unsigned _value): Pattern(u256(_value)) {}
+	// Matches a specific constant value.
+	Pattern(u256 const& _value): m_type(Push), m_requireDataMatch(true), m_data(_value) {}
+	// Matches a specific assembly item type or anything if not given.
+	Pattern(AssemblyItemType _type = UndefinedItem): m_type(_type) {}
+	// Matches a given instruction with given arguments
+	Pattern(Instruction _instruction, std::vector<Pattern> const& _arguments = {});
+	/// Sets this pattern to be part of the match group with the identifier @a _group.
+	/// Inside one rule, all patterns in the same match group have to match expressions from the
+	/// same expression equivalence class.
+	void setMatchGroup(unsigned _group, std::map<unsigned, Expression const*>& _matchGroups);
+	unsigned matchGroup() const { return m_matchGroup; }
+	bool matches(Expression const& _expr, ExpressionClasses const& _classes) const;
+
+	AssemblyItem toAssemblyItem(SourceLocation const& _location) const;
+	std::vector<Pattern> arguments() const { return m_arguments; }
+
+	/// @returns the id of the matched expression if this pattern is part of a match group.
+	Id id() const { return matchGroupValue().id; }
+	/// @returns the data of the matched expression if this pattern is part of a match group.
+	u256 const& d() const { return matchGroupValue().item->data(); }
+
+	std::string toString() const;
+
+private:
+	bool matchesBaseItem(AssemblyItem const* _item) const;
+	Expression const& matchGroupValue() const;
+
+	AssemblyItemType m_type;
+	bool m_requireDataMatch = false;
+	u256 m_data = 0;
+	std::vector<Pattern> m_arguments;
+	unsigned m_matchGroup = 0;
+	std::map<unsigned, Expression const*>* m_matchGroups = nullptr;
+};
+
+/**
+ * Template for a new expression that can be built from matched patterns.
+ */
+struct ExpressionTemplate
+{
+	using Expression = ExpressionClasses::Expression;
+	using Id = ExpressionClasses::Id;
+	explicit ExpressionTemplate(Pattern const& _pattern, SourceLocation const& _location);
+	std::string toString() const;
+	bool hasId = false;
+	/// Id of the matched expression, if available.
+	Id id = Id(-1);
+	// Otherwise, assembly item.
+	AssemblyItem item = UndefinedItem;
+	std::vector<ExpressionTemplate> arguments;
+};
+
+}
+}
diff --git a/libevmasm/GasMeter.cpp b/libevmasm/GasMeter.cpp
new file mode 100644
index 00000000..93583169
--- /dev/null
+++ b/libevmasm/GasMeter.cpp
@@ -0,0 +1,217 @@
+/*
+	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 GasMeter.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#include "GasMeter.h"
+#include <libevmasm/KnownState.h>
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+GasMeter::GasConsumption& GasMeter::GasConsumption::operator+=(GasConsumption const& _other)
+{
+	if (_other.isInfinite && !isInfinite)
+		*this = infinite();
+	if (isInfinite)
+		return *this;
+	bigint v = bigint(value) + _other.value;
+	if (v > numeric_limits<u256>::max())
+		*this = infinite();
+	else
+		value = u256(v);
+	return *this;
+}
+
+GasMeter::GasConsumption GasMeter::estimateMax(AssemblyItem const& _item)
+{
+	GasConsumption gas;
+	switch (_item.type())
+	{
+	case Push:
+	case PushTag:
+	case PushData:
+	case PushString:
+	case PushSub:
+	case PushSubSize:
+	case PushProgramSize:
+	case PushLibraryAddress:
+		gas = runGas(Instruction::PUSH1);
+		break;
+	case Tag:
+		gas = runGas(Instruction::JUMPDEST);
+		break;
+	case Operation:
+	{
+		ExpressionClasses& classes = m_state->expressionClasses();
+		gas = runGas(_item.instruction());
+		switch (_item.instruction())
+		{
+		case Instruction::SSTORE:
+		{
+			ExpressionClasses::Id slot = m_state->relativeStackElement(0);
+			ExpressionClasses::Id value = m_state->relativeStackElement(-1);
+			if (classes.knownZero(value) || (
+				m_state->storageContent().count(slot) &&
+				classes.knownNonZero(m_state->storageContent().at(slot))
+			))
+				gas += m_schedule.sstoreResetGas; //@todo take refunds into account
+			else
+				gas += m_schedule.sstoreSetGas;
+			break;
+		}
+		case Instruction::SLOAD:
+			gas += m_schedule.sloadGas;
+			break;
+		case Instruction::RETURN:
+			gas += memoryGas(0, -1);
+			break;
+		case Instruction::MLOAD:
+		case Instruction::MSTORE:
+			gas += memoryGas(classes.find(eth::Instruction::ADD, {
+				m_state->relativeStackElement(0),
+				classes.find(AssemblyItem(32))
+			}));
+			break;
+		case Instruction::MSTORE8:
+			gas += memoryGas(classes.find(eth::Instruction::ADD, {
+				m_state->relativeStackElement(0),
+				classes.find(AssemblyItem(1))
+			}));
+			break;
+		case Instruction::SHA3:
+			gas = m_schedule.sha3Gas;
+			gas += wordGas(m_schedule.sha3WordGas, m_state->relativeStackElement(-1));
+			gas += memoryGas(0, -1);
+			break;
+		case Instruction::CALLDATACOPY:
+		case Instruction::CODECOPY:
+			gas += memoryGas(0, -2);
+			gas += wordGas(m_schedule.copyGas, m_state->relativeStackElement(-2));
+			break;
+		case Instruction::EXTCODECOPY:
+			gas += memoryGas(-1, -3);
+			gas += wordGas(m_schedule.copyGas, m_state->relativeStackElement(-3));
+			break;
+		case Instruction::LOG0:
+		case Instruction::LOG1:
+		case Instruction::LOG2:
+		case Instruction::LOG3:
+		case Instruction::LOG4:
+		{
+			unsigned n = unsigned(_item.instruction()) - unsigned(Instruction::LOG0);
+			gas = m_schedule.logGas + m_schedule.logTopicGas * n;
+			gas += memoryGas(0, -1);
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
+				gas += m_schedule.logDataGas * (*value);
+			else
+				gas = GasConsumption::infinite();
+			break;
+		}
+		case Instruction::CALL:
+		case Instruction::CALLCODE:
+		case Instruction::DELEGATECALL:
+		{
+			gas = m_schedule.callGas;
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(0)))
+				gas += (*value);
+			else
+				gas = GasConsumption::infinite();
+			if (_item.instruction() == Instruction::CALL)
+				gas += m_schedule.callNewAccountGas; // We very rarely know whether the address exists.
+			int valueSize = _item.instruction() == Instruction::DELEGATECALL ? 0 : 1;
+			if (!classes.knownZero(m_state->relativeStackElement(-1 - valueSize)))
+				gas += m_schedule.callValueTransferGas;
+			gas += memoryGas(-2 - valueSize, -3 - valueSize);
+			gas += memoryGas(-4 - valueSize, -5 - valueSize);
+			break;
+		}
+		case Instruction::CREATE:
+			gas = m_schedule.createGas;
+			gas += memoryGas(-1, -2);
+			break;
+		case Instruction::EXP:
+			gas = m_schedule.expGas;
+			if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
+				gas += m_schedule.expByteGas * (32 - (h256(*value).firstBitSet() / 8));
+			else
+				gas += m_schedule.expByteGas * 32;
+			break;
+		default:
+			break;
+		}
+		break;
+	}
+	default:
+		gas = GasConsumption::infinite();
+		break;
+	}
+
+	m_state->feedItem(_item);
+	return gas;
+}
+
+GasMeter::GasConsumption GasMeter::wordGas(u256 const& _multiplier, ExpressionClasses::Id _position)
+{
+	u256 const* value = m_state->expressionClasses().knownConstant(_position);
+	if (!value)
+		return GasConsumption::infinite();
+	return GasConsumption(_multiplier * ((*value + 31) / 32));
+}
+
+GasMeter::GasConsumption GasMeter::memoryGas(ExpressionClasses::Id _position)
+{
+	u256 const* value = m_state->expressionClasses().knownConstant(_position);
+	if (!value)
+		return GasConsumption::infinite();
+	if (*value < m_largestMemoryAccess)
+		return GasConsumption(u256(0));
+	u256 previous = m_largestMemoryAccess;
+	m_largestMemoryAccess = *value;
+	auto memGas = [=](u256 const& pos) -> u256
+	{
+		u256 size = (pos + 31) / 32;
+		return m_schedule.memoryGas * size + size * size / m_schedule.quadCoeffDiv;
+	};
+	return memGas(*value) - memGas(previous);
+}
+
+GasMeter::GasConsumption GasMeter::memoryGas(int _stackPosOffset, int _stackPosSize)
+{
+	ExpressionClasses& classes = m_state->expressionClasses();
+	if (classes.knownZero(m_state->relativeStackElement(_stackPosSize)))
+		return GasConsumption(0);
+	else
+		return memoryGas(classes.find(eth::Instruction::ADD, {
+			m_state->relativeStackElement(_stackPosOffset),
+			m_state->relativeStackElement(_stackPosSize)
+		}));
+}
+
+u256 GasMeter::runGas(Instruction _instruction, EVMSchedule const& _es)
+{
+	if (_instruction == Instruction::JUMPDEST)
+		return 1;
+
+	int tier = instructionInfo(_instruction).gasPriceTier;
+	assertThrow(tier != InvalidTier, OptimizerException, "Invalid gas tier.");
+	return _es.tierStepGas[tier];
+}
+
+
diff --git a/libevmasm/GasMeter.h b/libevmasm/GasMeter.h
new file mode 100644
index 00000000..b11a63a5
--- /dev/null
+++ b/libevmasm/GasMeter.h
@@ -0,0 +1,102 @@
+/*
+	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 GasMeter.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#pragma once
+
+#include <ostream>
+#include <tuple>
+#include <libevmasm/ExpressionClasses.h>
+#include <libevmasm/AssemblyItem.h>
+#include <libethcore/ChainOperationParams.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class KnownState;
+
+// TODO: FIXME: HOMESTEAD: XXX: @chfast populate m_schedule from an ExtVMFace instance via ExtVMFace::evmSchedule.
+
+/**
+ * Class that helps computing the maximum gas consumption for instructions.
+ * Has to be initialized with a certain known state that will be automatically updated for
+ * each call to estimateMax. These calls have to supply strictly subsequent AssemblyItems.
+ * A new gas meter has to be constructed (with a new state) for control flow changes.
+ */
+class GasMeter
+{
+public:
+	struct GasConsumption
+	{
+		GasConsumption(u256 _value = 0, bool _infinite = false): value(_value), isInfinite(_infinite) {}
+		static GasConsumption infinite() { return GasConsumption(0, true); }
+
+		GasConsumption& operator+=(GasConsumption const& _other);
+		bool operator<(GasConsumption const& _other) const { return this->tuple() < _other.tuple(); }
+
+		std::tuple<bool const&, u256 const&> tuple() const { return std::tie(isInfinite, value); }
+
+		u256 value;
+		bool isInfinite;
+	};
+
+	/// Constructs a new gas meter given the current state.
+	explicit GasMeter(std::shared_ptr<KnownState> const& _state, u256 const& _largestMemoryAccess = 0):
+		m_state(_state), m_largestMemoryAccess(_largestMemoryAccess) {}
+
+	/// @returns an upper bound on the gas consumed by the given instruction and updates
+	/// the state.
+	GasConsumption estimateMax(AssemblyItem const& _item);
+
+	u256 const& largestMemoryAccess() const { return m_largestMemoryAccess; }
+
+	u256 runGas(Instruction _instruction) const { return runGas(_instruction, m_schedule); }
+	static u256 runGas(Instruction _instruction, EVMSchedule const& _es);
+
+private:
+	/// @returns _multiplier * (_value + 31) / 32, if _value is a known constant and infinite otherwise.
+	GasConsumption wordGas(u256 const& _multiplier, ExpressionClasses::Id _value);
+	/// @returns the gas needed to access the given memory position.
+	/// @todo this assumes that memory was never accessed before and thus over-estimates gas usage.
+	GasConsumption memoryGas(ExpressionClasses::Id _position);
+	/// @returns the memory gas for accessing the memory at a specific offset for a number of bytes
+	/// given as values on the stack at the given relative positions.
+	GasConsumption memoryGas(int _stackPosOffset, int _stackPosSize);
+
+	std::shared_ptr<KnownState> m_state;
+	/// Largest point where memory was accessed since the creation of this object.
+	u256 m_largestMemoryAccess;
+
+	EVMSchedule m_schedule;
+};
+
+inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption const& _consumption)
+{
+	if (_consumption.isInfinite)
+		return _str << "[???]";
+	else
+		return _str << std::dec << _consumption.value;
+}
+
+
+}
+}
diff --git a/libevmasm/KnownState.cpp b/libevmasm/KnownState.cpp
new file mode 100644
index 00000000..dd269ff4
--- /dev/null
+++ b/libevmasm/KnownState.cpp
@@ -0,0 +1,411 @@
+/*
+	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 <libdevcore/SHA3.h>
+#include <libevmasm/AssemblyItem.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+ostream& KnownState::stream(ostream& _out) const
+{
+	auto streamExpressionClass = [this](ostream& _out, Id _id)
+	{
+		auto const& expr = m_expressionClasses->representative(_id);
+		_out << "  " << dec << _id << ": ";
+		if (!expr.item)
+			_out << " no item";
+		else if (expr.item->type() == UndefinedItem)
+			_out << " unknown " << int(expr.item->data());
+		else
+			_out << *expr.item;
+		if (expr.sequenceNumber)
+			_out << "@" << dec << expr.sequenceNumber;
+		_out << "(";
+		for (Id arg: expr.arguments)
+			_out << dec << arg << ",";
+		_out << ")" << endl;
+	};
+
+	_out << "=== State ===" << endl;
+	_out << "Stack height: " << dec << m_stackHeight << endl;
+	_out << "Equivalence classes: " << endl;
+	for (Id eqClass = 0; eqClass < m_expressionClasses->size(); ++eqClass)
+		streamExpressionClass(_out, eqClass);
+
+	_out << "Stack: " << endl;
+	for (auto const& it: m_stackElements)
+	{
+		_out << "  " << dec << it.first << ": ";
+		streamExpressionClass(_out, it.second);
+	}
+	_out << "Storage: " << endl;
+	for (auto const& it: m_storageContent)
+	{
+		_out << "  ";
+		streamExpressionClass(_out, it.first);
+		_out << ": ";
+		streamExpressionClass(_out, it.second);
+	}
+	_out << "Memory: " << endl;
+	for (auto const& it: m_memoryContent)
+	{
+		_out << "  ";
+		streamExpressionClass(_out, it.first);
+		_out << ": ";
+		streamExpressionClass(_out, it.second);
+	}
+
+	return _out;
+}
+
+KnownState::StoreOperation KnownState::feedItem(AssemblyItem const& _item, bool _copyItem)
+{
+	StoreOperation op;
+	if (_item.type() == Tag)
+	{
+		// can be ignored
+	}
+	else if (_item.type() != Operation)
+	{
+		assertThrow(_item.deposit() == 1, InvalidDeposit, "");
+		if (_item.pushedValue())
+			// only available after assembly stage, should not be used for optimisation
+			setStackElement(++m_stackHeight, m_expressionClasses->find(*_item.pushedValue()));
+		else
+			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.location()
+				)
+			);
+		else if (SemanticInformation::isSwapInstruction(_item))
+			swapStackElements(
+				m_stackHeight,
+				m_stackHeight - 1 - int(instruction) + int(Instruction::SWAP1),
+				_item.location()
+			);
+		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.location());
+
+			if (_item.instruction() == Instruction::SSTORE)
+				op = storeInStorage(arguments[0], arguments[1], _item.location());
+			else if (_item.instruction() == Instruction::SLOAD)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					loadFromStorage(arguments[0], _item.location())
+				);
+			else if (_item.instruction() == Instruction::MSTORE)
+				op = storeInMemory(arguments[0], arguments[1], _item.location());
+			else if (_item.instruction() == Instruction::MLOAD)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					loadFromMemory(arguments[0], _item.location())
+				);
+			else if (_item.instruction() == Instruction::SHA3)
+				setStackElement(
+					m_stackHeight + _item.deposit(),
+					applySha3(arguments.at(0), arguments.at(1), _item.location())
+				);
+			else
+			{
+				bool invMem = SemanticInformation::invalidatesMemory(_item.instruction());
+				bool invStor = SemanticInformation::invalidatesStorage(_item.instruction());
+				// We could be a bit more fine-grained here (CALL only invalidates part of
+				// memory, etc), but we do not for now.
+				if (invMem)
+					resetMemory();
+				if (invStor)
+					resetStorage();
+				if (invMem || invStor)
+					m_sequenceNumber += 2; // Increment by two because it can read and write
+				assertThrow(info.ret <= 1, InvalidDeposit, "");
+				if (info.ret == 1)
+					setStackElement(
+						m_stackHeight + _item.deposit(),
+						m_expressionClasses->find(_item, arguments, _copyItem)
+					);
+			}
+		}
+		m_stackElements.erase(
+			m_stackElements.upper_bound(m_stackHeight + _item.deposit()),
+			m_stackElements.end()
+		);
+		m_stackHeight += _item.deposit();
+	}
+	return op;
+}
+
+/// Helper function for KnownState::reduceToCommonKnowledge, removes everything from
+/// _this which is not in or not equal to the value in _other.
+template <class _Mapping> void intersect(_Mapping& _this, _Mapping const& _other)
+{
+	for (auto it = _this.begin(); it != _this.end();)
+		if (_other.count(it->first) && _other.at(it->first) == it->second)
+			++it;
+		else
+			it = _this.erase(it);
+}
+
+void KnownState::reduceToCommonKnowledge(KnownState const& _other, bool _combineSequenceNumbers)
+{
+	int stackDiff = m_stackHeight - _other.m_stackHeight;
+	for (auto it = m_stackElements.begin(); it != m_stackElements.end();)
+		if (_other.m_stackElements.count(it->first - stackDiff))
+		{
+			Id other = _other.m_stackElements.at(it->first - stackDiff);
+			if (it->second == other)
+				++it;
+			else
+			{
+				set<u256> theseTags = tagsInExpression(it->second);
+				set<u256> otherTags = tagsInExpression(other);
+				if (!theseTags.empty() && !otherTags.empty())
+				{
+					theseTags.insert(otherTags.begin(), otherTags.end());
+					it->second = tagUnion(theseTags);
+					++it;
+				}
+				else
+					it = m_stackElements.erase(it);
+			}
+		}
+		else
+			it = m_stackElements.erase(it);
+
+	// Use the smaller stack height. Essential to terminate in case of loops.
+	if (m_stackHeight > _other.m_stackHeight)
+	{
+		map<int, Id> shiftedStack;
+		for (auto const& stackElement: m_stackElements)
+			shiftedStack[stackElement.first - stackDiff] = stackElement.second;
+		m_stackElements = move(shiftedStack);
+		m_stackHeight = _other.m_stackHeight;
+	}
+
+	intersect(m_storageContent, _other.m_storageContent);
+	intersect(m_memoryContent, _other.m_memoryContent);
+	if (_combineSequenceNumbers)
+		m_sequenceNumber = max(m_sequenceNumber, _other.m_sequenceNumber);
+}
+
+bool KnownState::operator==(KnownState const& _other) const
+{
+	if (m_storageContent != _other.m_storageContent || m_memoryContent != _other.m_memoryContent)
+		return false;
+	int stackDiff = m_stackHeight - _other.m_stackHeight;
+	auto thisIt = m_stackElements.cbegin();
+	auto otherIt = _other.m_stackElements.cbegin();
+	for (; thisIt != m_stackElements.cend() && otherIt != _other.m_stackElements.cend(); ++thisIt, ++otherIt)
+		if (thisIt->first - stackDiff != otherIt->first || thisIt->second != otherIt->second)
+			return false;
+	return (thisIt == m_stackElements.cend() && otherIt == _other.m_stackElements.cend());
+}
+
+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 unknown equivalence class.
+	return m_stackElements[_stackHeight] =
+			m_expressionClasses->find(AssemblyItem(UndefinedItem, _stackHeight, _location));
+}
+
+KnownState::Id KnownState::relativeStackElement(int _stackOffset, SourceLocation const& _location)
+{
+	return stackElement(m_stackHeight + _stackOffset, _location);
+}
+
+void KnownState::clearTagUnions()
+{
+	for (auto it = m_stackElements.begin(); it != m_stackElements.end();)
+		if (m_tagUnions.left.count(it->second))
+			it = m_stackElements.erase(it);
+		else
+			++it;
+}
+
+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;
+}
+
+set<u256> KnownState::tagsInExpression(KnownState::Id _expressionId)
+{
+	if (m_tagUnions.left.count(_expressionId))
+		return m_tagUnions.left.at(_expressionId);
+	// Might be a tag, then return the set of itself.
+	ExpressionClasses::Expression expr = m_expressionClasses->representative(_expressionId);
+	if (expr.item && expr.item->type() == PushTag)
+		return set<u256>({expr.item->data()});
+	else
+		return set<u256>();
+}
+
+KnownState::Id KnownState::tagUnion(set<u256> _tags)
+{
+	if (m_tagUnions.right.count(_tags))
+		return m_tagUnions.right.at(_tags);
+	else
+	{
+		Id id = m_expressionClasses->newClass(SourceLocation());
+		m_tagUnions.right.insert(make_pair(_tags, id));
+		return id;
+	}
+}
+
diff --git a/libevmasm/KnownState.h b/libevmasm/KnownState.h
new file mode 100644
index 00000000..c1c602dc
--- /dev/null
+++ b/libevmasm/KnownState.h
@@ -0,0 +1,179 @@
+/*
+	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.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Contains knowledge about the state of the virtual machine at a specific instruction.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <set>
+#include <tuple>
+#include <memory>
+#include <ostream>
+#pragma warning(push)
+#pragma GCC diagnostic push
+#pragma clang diagnostic ignored "-Wredeclared-class-member"
+#include <boost/bimap.hpp>
+#pragma warning(pop)
+#pragma GCC diagnostic pop
+#include <libdevcore/CommonIO.h>
+#include <libdevcore/Exceptions.h>
+#include <libevmasm/ExpressionClasses.h>
+#include <libevmasm/SemanticInformation.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+using AssemblyItems = std::vector<AssemblyItem>;
+
+/**
+ * Class to infer and store knowledge about the state of the virtual machine at a specific
+ * instruction.
+ *
+ * The general workings are that for each assembly item that is fed, an equivalence class is
+ * derived from the operation and the equivalence class of its arguments. DUPi, SWAPi and some
+ * arithmetic instructions are used to infer equivalences while these classes are determined.
+ */
+class KnownState
+{
+public:
+	using Id = ExpressionClasses::Id;
+	struct StoreOperation
+	{
+		enum Target { Invalid, Memory, Storage };
+		StoreOperation(): target(Invalid), sequenceNumber(-1) {}
+		StoreOperation(
+			Target _target,
+			Id _slot,
+			unsigned _sequenceNumber,
+			Id _expression
+		): target(_target), slot(_slot), sequenceNumber(_sequenceNumber), expression(_expression) {}
+		bool isValid() const { return target != Invalid; }
+		Target target;
+		Id slot;
+		unsigned sequenceNumber;
+		Id expression;
+	};
+
+	explicit KnownState(
+		std::shared_ptr<ExpressionClasses> _expressionClasses = std::make_shared<ExpressionClasses>()
+	): m_expressionClasses(_expressionClasses)
+	{
+	}
+
+	/// Streams debugging information to @a _out.
+	std::ostream& stream(std::ostream& _out) const;
+
+	/// Feeds the item into the system for analysis.
+	/// @returns a possible store operation
+	StoreOperation feedItem(AssemblyItem const& _item, bool _copyItem = false);
+
+	/// Resets any knowledge about storage.
+	void resetStorage() { m_storageContent.clear(); }
+	/// Resets any knowledge about storage.
+	void resetMemory() { m_memoryContent.clear(); }
+	/// Resets any knowledge about the current stack.
+	void resetStack() { m_stackElements.clear(); m_stackHeight = 0; }
+	/// Resets any knowledge.
+	void reset() { resetStorage(); resetMemory(); resetStack(); }
+
+	unsigned sequenceNumber() const { return m_sequenceNumber; }
+
+	/// Replaces the state by the intersection with _other, i.e. only equal knowledge is retained.
+	/// If the stack heighht is different, the smaller one is used and the stack is compared
+	/// relatively.
+	/// @param _combineSequenceNumbers if true, sets the sequence number to the maximum of both
+	void reduceToCommonKnowledge(KnownState const& _other, bool _combineSequenceNumbers);
+
+	/// @returns a shared pointer to a copy of this state.
+	std::shared_ptr<KnownState> copy() const { return std::make_shared<KnownState>(*this); }
+
+	/// @returns true if the knowledge about the state of both objects is (known to be) equal.
+	bool operator==(KnownState const& _other) const;
+
+	/// Retrieves the current equivalence class fo the given stack element (or generates a new
+	/// one if it does not exist yet).
+	Id stackElement(int _stackHeight, SourceLocation const& _location);
+	/// @returns the stackElement relative to the current stack height.
+	Id relativeStackElement(int _stackOffset, SourceLocation const& _location = SourceLocation());
+
+	/// @returns its set of tags if the given expression class is a known tag union; returns a set
+	/// containing the tag if it is a PushTag expression and the empty set otherwise.
+	std::set<u256> tagsInExpression(Id _expressionId);
+	/// During analysis, different tags on the stack are partially treated as the same class.
+	/// This removes such classes not to confuse later analyzers.
+	void clearTagUnions();
+
+	int stackHeight() const { return m_stackHeight; }
+	std::map<int, Id> const& stackElements() const { return m_stackElements; }
+	ExpressionClasses& expressionClasses() const { return *m_expressionClasses; }
+
+	std::map<Id, Id> const& storageContent() const { return m_storageContent; }
+
+private:
+	/// Assigns a new equivalence class to the next sequence number of the given stack element.
+	void setStackElement(int _stackHeight, Id _class);
+	/// Swaps the given stack elements in their next sequence number.
+	void swapStackElements(int _stackHeightA, int _stackHeightB, SourceLocation const& _location);
+
+	/// Increments the sequence number, deletes all storage information that might be overwritten
+	/// and stores the new value at the given slot.
+	/// @returns the store operation, which might be invalid if storage was not modified
+	StoreOperation storeInStorage(Id _slot, Id _value, SourceLocation const& _location);
+	/// Retrieves the current value at the given slot in storage or creates a new special sload class.
+	Id loadFromStorage(Id _slot, SourceLocation const& _location);
+	/// Increments the sequence number, deletes all memory information that might be overwritten
+	/// and stores the new value at the given slot.
+	/// @returns the store operation, which might be invalid if memory was not modified
+	StoreOperation storeInMemory(Id _slot, Id _value, SourceLocation const& _location);
+	/// Retrieves the current value at the given slot in memory or creates a new special mload class.
+	Id loadFromMemory(Id _slot, SourceLocation const& _location);
+	/// Finds or creates a new expression that applies the sha3 hash function to the contents in memory.
+	Id applySha3(Id _start, Id _length, SourceLocation const& _location);
+
+	/// @returns a new or already used Id representing the given set of tags.
+	Id tagUnion(std::set<u256> _tags);
+
+	/// Current stack height, can be negative.
+	int m_stackHeight = 0;
+	/// Current stack layout, mapping stack height -> equivalence class
+	std::map<int, Id> m_stackElements;
+	/// Current sequence number, this is incremented with each modification to storage or memory.
+	unsigned m_sequenceNumber = 1;
+	/// Knowledge about storage content.
+	std::map<Id, Id> m_storageContent;
+	/// Knowledge about memory content. Keys are memory addresses, note that the values overlap
+	/// and are not contained here if they are not completely known.
+	std::map<Id, Id> m_memoryContent;
+	/// Keeps record of all sha3 hashes that are computed.
+	std::map<std::vector<Id>, Id> m_knownSha3Hashes;
+	/// Structure containing the classes of equivalent expressions.
+	std::shared_ptr<ExpressionClasses> m_expressionClasses;
+	/// Container for unions of tags stored on the stack.
+	boost::bimap<Id, std::set<u256>> m_tagUnions;
+};
+
+}
+}
diff --git a/libevmasm/LinkerObject.cpp b/libevmasm/LinkerObject.cpp
new file mode 100644
index 00000000..ceb864a1
--- /dev/null
+++ b/libevmasm/LinkerObject.cpp
@@ -0,0 +1,62 @@
+/*
+	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 LinkerObject.cpp
+ * @author Christian R <c@ethdev.com>
+ * @date 2015
+ */
+
+#include <libevmasm/LinkerObject.h>
+#include <libdevcore/CommonData.h>
+
+using namespace dev;
+using namespace dev::eth;
+using namespace std;
+
+void LinkerObject::append(LinkerObject const& _other)
+{
+	for (auto const& ref: _other.linkReferences)
+		linkReferences[ref.first + bytecode.size()] = ref.second;
+	bytecode += _other.bytecode;
+}
+
+void LinkerObject::link(map<string, h160> const& _libraryAddresses)
+{
+	std::map<size_t, std::string> remainingRefs;
+	for (auto const& linkRef: linkReferences)
+	{
+		auto it = _libraryAddresses.find(linkRef.second);
+		if (it == _libraryAddresses.end())
+			remainingRefs.insert(linkRef);
+		else
+			it->second.ref().copyTo(ref(bytecode).cropped(linkRef.first, 20));
+	}
+	linkReferences.swap(remainingRefs);
+}
+
+string LinkerObject::toHex() const
+{
+	string hex = dev::toHex(bytecode);
+	for (auto const& ref: linkReferences)
+	{
+		size_t pos = ref.first * 2;
+		string const& name = ref.second;
+		hex[pos] = hex[pos + 1] = hex[pos + 38] = hex[pos + 39] = '_';
+		for (size_t i = 0; i < 36; ++i)
+			hex[pos + 2 + i] = i < name.size() ? name[i] : '_';
+	}
+	return hex;
+}
diff --git a/libevmasm/LinkerObject.h b/libevmasm/LinkerObject.h
new file mode 100644
index 00000000..83d2bd7e
--- /dev/null
+++ b/libevmasm/LinkerObject.h
@@ -0,0 +1,55 @@
+/*
+	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 Assembly.h
+ * @author Gav Wood <i@gavwood.com>
+ * @date 2014
+ */
+
+#pragma once
+
+#include <libdevcore/Common.h>
+#include <libdevcore/FixedHash.h>
+
+namespace dev
+{
+namespace eth
+{
+
+/**
+ * Binary object that potentially still needs to be linked (i.e. addresses of other contracts
+ * need to be filled in).
+ */
+struct LinkerObject
+{
+	bytes bytecode;
+	/// Map from offsets in bytecode to library identifiers. The addresses starting at those offsets
+	/// need to be replaced by the actual addresses by the linker.
+	std::map<size_t, std::string> linkReferences;
+
+	/// Appends the bytecode of @a _other and incorporates its link references.
+	void append(LinkerObject const& _other);
+
+	/// Links the given libraries by replacing their uses in the code and removes them from the references.
+	void link(std::map<std::string, h160> const& _libraryAddresses);
+
+	/// @returns a hex representation of the bytecode of the given object, replacing unlinked
+	/// addresses by placeholders.
+	std::string toHex() const;
+};
+
+}
+}
diff --git a/libevmasm/PathGasMeter.cpp b/libevmasm/PathGasMeter.cpp
new file mode 100644
index 00000000..8f7314f8
--- /dev/null
+++ b/libevmasm/PathGasMeter.cpp
@@ -0,0 +1,128 @@
+/*
+	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 PathGasMeter.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#include "PathGasMeter.h"
+#include <libevmasm/KnownState.h>
+#include <libevmasm/SemanticInformation.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+PathGasMeter::PathGasMeter(AssemblyItems const& _items):
+	m_items(_items)
+{
+	for (size_t i = 0; i < m_items.size(); ++i)
+		if (m_items[i].type() == Tag)
+			m_tagPositions[m_items[i].data()] = i;
+}
+
+GasMeter::GasConsumption PathGasMeter::estimateMax(
+	size_t _startIndex,
+	shared_ptr<KnownState> const& _state
+)
+{
+	auto path = unique_ptr<GasPath>(new GasPath());
+	path->index = _startIndex;
+	path->state = _state->copy();
+	m_queue.push_back(move(path));
+
+	GasMeter::GasConsumption gas;
+	while (!m_queue.empty() && !gas.isInfinite)
+		gas = max(gas, handleQueueItem());
+	return gas;
+}
+
+GasMeter::GasConsumption PathGasMeter::handleQueueItem()
+{
+	assertThrow(!m_queue.empty(), OptimizerException, "");
+
+	unique_ptr<GasPath> path = move(m_queue.back());
+	m_queue.pop_back();
+
+	shared_ptr<KnownState> state = path->state;
+	GasMeter meter(state, path->largestMemoryAccess);
+	ExpressionClasses& classes = state->expressionClasses();
+	GasMeter::GasConsumption gas = path->gas;
+	size_t index = path->index;
+
+	if (index >= m_items.size() || (index > 0 && m_items.at(index).type() != Tag))
+		// Invalid jump usually provokes an out-of-gas exception, but we want to give an upper
+		// bound on the gas that is needed without changing the behaviour, so it is fine to
+		// return the current gas value.
+		return gas;
+
+	set<u256> jumpTags;
+	for (; index < m_items.size() && !gas.isInfinite; ++index)
+	{
+		bool branchStops = false;
+		jumpTags.clear();
+		AssemblyItem const& item = m_items.at(index);
+		if (item.type() == Tag || item == AssemblyItem(eth::Instruction::JUMPDEST))
+		{
+			// Do not allow any backwards jump. This is quite restrictive but should work for
+			// the simplest things.
+			if (path->visitedJumpdests.count(index))
+				return GasMeter::GasConsumption::infinite();
+			path->visitedJumpdests.insert(index);
+		}
+		else if (item == AssemblyItem(eth::Instruction::JUMP))
+		{
+			branchStops = true;
+			jumpTags = state->tagsInExpression(state->relativeStackElement(0));
+			if (jumpTags.empty()) // unknown jump destination
+				return GasMeter::GasConsumption::infinite();
+		}
+		else if (item == AssemblyItem(eth::Instruction::JUMPI))
+		{
+			ExpressionClasses::Id condition = state->relativeStackElement(-1);
+			if (classes.knownNonZero(condition) || !classes.knownZero(condition))
+			{
+				jumpTags = state->tagsInExpression(state->relativeStackElement(0));
+				if (jumpTags.empty()) // unknown jump destination
+					return GasMeter::GasConsumption::infinite();
+			}
+			branchStops = classes.knownNonZero(condition);
+		}
+		else if (SemanticInformation::altersControlFlow(item))
+			branchStops = true;
+
+		gas += meter.estimateMax(item);
+
+		for (u256 const& tag: jumpTags)
+		{
+			auto newPath = unique_ptr<GasPath>(new GasPath());
+			newPath->index = m_items.size();
+			if (m_tagPositions.count(tag))
+				newPath->index = m_tagPositions.at(tag);
+			newPath->gas = gas;
+			newPath->largestMemoryAccess = meter.largestMemoryAccess();
+			newPath->state = state->copy();
+			newPath->visitedJumpdests = path->visitedJumpdests;
+			m_queue.push_back(move(newPath));
+		}
+
+		if (branchStops)
+			break;
+	}
+
+	return gas;
+}
diff --git a/libevmasm/PathGasMeter.h b/libevmasm/PathGasMeter.h
new file mode 100644
index 00000000..1ada460a
--- /dev/null
+++ b/libevmasm/PathGasMeter.h
@@ -0,0 +1,66 @@
+/*
+	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 PathGasMeter.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ */
+
+#pragma once
+
+#include <set>
+#include <vector>
+#include <memory>
+#include <libevmasm/GasMeter.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class KnownState;
+
+struct GasPath
+{
+	size_t index = 0;
+	std::shared_ptr<KnownState> state;
+	u256 largestMemoryAccess;
+	GasMeter::GasConsumption gas;
+	std::set<size_t> visitedJumpdests;
+};
+
+/**
+ * Computes an upper bound on the gas usage of a computation starting at a certain position in
+ * a list of AssemblyItems in a given state until the computation stops.
+ * Can be used to estimate the gas usage of functions on any given input.
+ */
+class PathGasMeter
+{
+public:
+	PathGasMeter(AssemblyItems const& _items);
+
+	GasMeter::GasConsumption estimateMax(size_t _startIndex, std::shared_ptr<KnownState> const& _state);
+
+private:
+	GasMeter::GasConsumption handleQueueItem();
+
+	std::vector<std::unique_ptr<GasPath>> m_queue;
+	std::map<u256, size_t> m_tagPositions;
+	AssemblyItems const& m_items;
+};
+
+}
+}
diff --git a/libevmasm/SemanticInformation.cpp b/libevmasm/SemanticInformation.cpp
new file mode 100644
index 00000000..ea579b83
--- /dev/null
+++ b/libevmasm/SemanticInformation.cpp
@@ -0,0 +1,181 @@
+/*
+	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 SemanticInformation.cpp
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Helper to provide semantic information about assembly items.
+ */
+
+#include <libevmasm/SemanticInformation.h>
+#include <libevmasm/AssemblyItem.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+bool SemanticInformation::breaksCSEAnalysisBlock(AssemblyItem const& _item)
+{
+	switch (_item.type())
+	{
+	default:
+	case UndefinedItem:
+	case Tag:
+		return true;
+	case Push:
+	case PushString:
+	case PushTag:
+	case PushSub:
+	case PushSubSize:
+	case PushProgramSize:
+	case PushData:
+	case PushLibraryAddress:
+		return false;
+	case Operation:
+	{
+		if (isSwapInstruction(_item) || isDupInstruction(_item))
+			return false;
+		if (_item.instruction() == Instruction::GAS || _item.instruction() == Instruction::PC)
+			return true; // GAS and PC assume a specific order of opcodes
+		if (_item.instruction() == Instruction::MSIZE)
+			return true; // msize is modified already by memory access, avoid that for now
+		InstructionInfo info = instructionInfo(_item.instruction());
+		if (_item.instruction() == Instruction::SSTORE)
+			return false;
+		if (_item.instruction() == Instruction::MSTORE)
+			return false;
+		//@todo: We do not handle the following memory instructions for now:
+		// calldatacopy, codecopy, extcodecopy, mstore8,
+		// msize (note that msize also depends on memory read access)
+
+		// the second requirement will be lifted once it is implemented
+		return info.sideEffects || info.args > 2;
+	}
+	}
+}
+
+bool SemanticInformation::isCommutativeOperation(AssemblyItem const& _item)
+{
+	if (_item.type() != Operation)
+		return false;
+	switch (_item.instruction())
+	{
+	case Instruction::ADD:
+	case Instruction::MUL:
+	case Instruction::EQ:
+	case Instruction::AND:
+	case Instruction::OR:
+	case Instruction::XOR:
+		return true;
+	default:
+		return false;
+	}
+}
+
+bool SemanticInformation::isDupInstruction(AssemblyItem const& _item)
+{
+	if (_item.type() != Operation)
+		return false;
+	return Instruction::DUP1 <= _item.instruction() && _item.instruction() <= Instruction::DUP16;
+}
+
+bool SemanticInformation::isSwapInstruction(AssemblyItem const& _item)
+{
+	if (_item.type() != Operation)
+		return false;
+	return Instruction::SWAP1 <= _item.instruction() && _item.instruction() <= Instruction::SWAP16;
+}
+
+bool SemanticInformation::isJumpInstruction(AssemblyItem const& _item)
+{
+	return _item == AssemblyItem(Instruction::JUMP) || _item == AssemblyItem(Instruction::JUMPI);
+}
+
+bool SemanticInformation::altersControlFlow(AssemblyItem const& _item)
+{
+	if (_item.type() != Operation)
+		return false;
+	switch (_item.instruction())
+	{
+	// note that CALL, CALLCODE and CREATE do not really alter the control flow, because we
+	// continue on the next instruction
+	case Instruction::JUMP:
+	case Instruction::JUMPI:
+	case Instruction::RETURN:
+	case Instruction::SUICIDE:
+	case Instruction::STOP:
+		return true;
+	default:
+		return false;
+	}
+}
+
+
+bool SemanticInformation::isDeterministic(AssemblyItem const& _item)
+{
+	if (_item.type() != Operation)
+		return true;
+
+	switch (_item.instruction())
+	{
+	case Instruction::CALL:
+	case Instruction::CALLCODE:
+	case Instruction::DELEGATECALL:
+	case Instruction::CREATE:
+	case Instruction::GAS:
+	case Instruction::PC:
+	case Instruction::MSIZE: // depends on previous writes and reads, not only on content
+	case Instruction::BALANCE: // depends on previous calls
+	case Instruction::EXTCODESIZE:
+		return false;
+	default:
+		return true;
+	}
+}
+
+bool SemanticInformation::invalidatesMemory(Instruction _instruction)
+{
+	switch (_instruction)
+	{
+	case Instruction::CALLDATACOPY:
+	case Instruction::CODECOPY:
+	case Instruction::EXTCODECOPY:
+	case Instruction::MSTORE:
+	case Instruction::MSTORE8:
+	case Instruction::CALL:
+	case Instruction::CALLCODE:
+	case Instruction::DELEGATECALL:
+		return true;
+	default:
+		return false;
+	}
+}
+
+bool SemanticInformation::invalidatesStorage(Instruction _instruction)
+{
+	switch (_instruction)
+	{
+	case Instruction::CALL:
+	case Instruction::CALLCODE:
+	case Instruction::DELEGATECALL:
+	case Instruction::CREATE:
+	case Instruction::SSTORE:
+		return true;
+	default:
+		return false;
+	}
+}
diff --git a/libevmasm/SemanticInformation.h b/libevmasm/SemanticInformation.h
new file mode 100644
index 00000000..094f4591
--- /dev/null
+++ b/libevmasm/SemanticInformation.h
@@ -0,0 +1,59 @@
+/*
+	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 SemanticInformation.h
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Helper to provide semantic information about assembly items.
+ */
+
+#pragma once
+
+#include <libevmcore/Instruction.h>
+
+namespace dev
+{
+namespace eth
+{
+
+class AssemblyItem;
+
+/**
+ * Helper functions to provide context-independent information about assembly items.
+ */
+struct SemanticInformation
+{
+	/// @returns true if the given items starts a new block for common subexpression analysis.
+	static bool breaksCSEAnalysisBlock(AssemblyItem const& _item);
+	/// @returns true if the item is a two-argument operation whose value does not depend on the
+	/// order of its arguments.
+	static bool isCommutativeOperation(AssemblyItem const& _item);
+	static bool isDupInstruction(AssemblyItem const& _item);
+	static bool isSwapInstruction(AssemblyItem const& _item);
+	static bool isJumpInstruction(AssemblyItem const& _item);
+	static bool altersControlFlow(AssemblyItem const& _item);
+	/// @returns false if the value put on the stack by _item depends on anything else than
+	/// the information in the current block header, memory, storage or stack.
+	static bool isDeterministic(AssemblyItem const& _item);
+	/// @returns true if the given instruction modifies memory.
+	static bool invalidatesMemory(Instruction _instruction);
+	/// @returns true if the given instruction modifies storage (even indirectly).
+	static bool invalidatesStorage(Instruction _instruction);
+};
+
+}
+}
diff --git a/libevmasm/SourceLocation.h b/libevmasm/SourceLocation.h
new file mode 100644
index 00000000..b8b57b60
--- /dev/null
+++ b/libevmasm/SourceLocation.h
@@ -0,0 +1,102 @@
+/*
+    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/>.
+*/
+/**
+ * @author Lefteris Karapetsas <lefteris@ethdev.com>
+ * @date 2015
+ * Represents a location in a source file
+ */
+
+#pragma once
+
+#include <memory>
+#include <string>
+#include <ostream>
+#include <tuple>
+
+namespace dev
+{
+
+/**
+ * Representation of an interval of source positions.
+ * The interval includes start and excludes end.
+ */
+struct SourceLocation
+{
+	SourceLocation(int _start, int _end, std::shared_ptr<std::string const> _sourceName):
+		start(_start), end(_end), sourceName(_sourceName) { }
+	SourceLocation(): start(-1), end(-1) { }
+
+	SourceLocation(SourceLocation const& _other):
+		start(_other.start),
+		end(_other.end),
+		sourceName(_other.sourceName)
+	{}
+
+	SourceLocation& operator=(SourceLocation const& _other)
+	{
+		if (&_other == this)
+			return *this;
+
+		start = _other.start;
+		end = _other.end;
+		sourceName = _other.sourceName;
+		return *this;
+	}
+
+	bool operator==(SourceLocation const& _other) const { return start == _other.start && end == _other.end;}
+	bool operator!=(SourceLocation const& _other) const { return !operator==(_other); }
+	inline bool operator<(SourceLocation const& _other) const;
+	inline bool contains(SourceLocation const& _other) const;
+	inline bool intersects(SourceLocation const& _other) const;
+
+	bool isEmpty() const { return start == -1 && end == -1; }
+
+	int start;
+	int end;
+	std::shared_ptr<std::string const> sourceName;
+};
+
+/// Stream output for Location (used e.g. in boost exceptions).
+inline std::ostream& operator<<(std::ostream& _out, SourceLocation const& _location)
+{
+	if (_location.isEmpty())
+		return _out << "NO_LOCATION_SPECIFIED";
+	return _out << *_location.sourceName << "[" << _location.start << "," << _location.end << ")";
+}
+
+bool SourceLocation::operator<(SourceLocation const& _other) const
+{
+	if (!sourceName || !_other.sourceName)
+		return int(!!sourceName) < int(!!_other.sourceName);
+	return make_tuple(*sourceName, start, end) < make_tuple(*_other.sourceName, _other.start, _other.end);
+}
+
+bool SourceLocation::contains(SourceLocation const& _other) const
+{
+	if (isEmpty() || _other.isEmpty() || !sourceName || !_other.sourceName || *sourceName != *_other.sourceName)
+		return false;
+	return start <= _other.start && _other.end <= end;
+}
+
+bool SourceLocation::intersects(SourceLocation const& _other) const
+{
+	if (isEmpty() || _other.isEmpty() || !sourceName || !_other.sourceName || *sourceName != *_other.sourceName)
+		return false;
+	return _other.start < end && start < _other.end;
+}
+
+}
diff --git a/libevmasm/Version.cpp b/libevmasm/Version.cpp
new file mode 100644
index 00000000..16b510b6
--- /dev/null
+++ b/libevmasm/Version.cpp
@@ -0,0 +1,38 @@
+/*
+	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/>.
+*/
+/**
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Versioning.
+ */
+
+#include <libevmasm/Version.h>
+#include <string>
+#include <ethereum/BuildInfo.h>
+#include <libdevcore/Common.h>
+
+using namespace dev;
+using namespace std;
+
+char const* dev::eth::VersionNumberLibEvmAsm = ETH_PROJECT_VERSION;
+extern string const dev::eth::VersionStringLibEvmAsm =
+	string(dev::eth::VersionNumberLibEvmAsm) +
+	"-" +
+	string(DEV_QUOTED(ETH_COMMIT_HASH)).substr(0, 8) +
+	(ETH_CLEAN_REPO ? "" : "*") +
+	"/" DEV_QUOTED(ETH_BUILD_TYPE) "-" DEV_QUOTED(ETH_BUILD_PLATFORM);
+
diff --git a/libevmasm/Version.h b/libevmasm/Version.h
new file mode 100644
index 00000000..8cba6e83
--- /dev/null
+++ b/libevmasm/Version.h
@@ -0,0 +1,36 @@
+/*
+	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/>.
+*/
+/**
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Versioning.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace dev
+{
+namespace eth
+{
+
+extern char const* VersionNumberLibEvmAsm;
+extern std::string const VersionStringLibEvmAsm;
+
+}
+}