Merge branch 'develop' of github.com:ethereum/cpp-ethereum into develop

libevmasm/Assembly.cpp

@@ -311,54 +311,45 @@ Assembly& Assembly::optimise(bool _enable)
 		copt << toString(*this);
 		count = 0;
 
-		//@todo CFG interface should be a generator, that returns an item and a pointer to a
-		// knownstate, which has to replace the current state if it is not null.
-		// Feed these items to the CSE, but also store them and replace the stored version
-		// if the items generated by the CSE are shorter. (or even use less gas?)
-		copt << "Performing control flow analysis...";
+		copt << "Performing optimisation...";
 		{
 			ControlFlowGraph cfg(m_items);
-			AssemblyItems optItems;
+			AssemblyItems optimisedItems;
 			for (BasicBlock const& block: cfg.optimisedBlocks())
-				copy(m_items.begin() + block.begin, m_items.begin() + block.end,
-					 back_inserter(optItems));
-			if (optItems.size() < m_items.size())
 			{
-				copt << "Old size: " << m_items.size() << ", new size: " << optItems.size();
-				m_items = move(optItems);
-				count++;
-			}
-		}
-
-		copt << "Performing common subexpression elimination...";
-		for (auto iter = m_items.begin(); iter != m_items.end();)
-		{
-			//@todo use only a single state / expression classes instance.
-			KnownState state(make_shared<ExpressionClasses>());
-			CommonSubexpressionEliminator eliminator(state);
-			auto orig = iter;
-			iter = eliminator.feedItems(iter, m_items.end());
-			AssemblyItems optItems;
-			bool shouldReplace = false;
-			try
-			{
-				optItems = eliminator.getOptimizedItems();
-				shouldReplace = (optItems.size() < size_t(iter - orig));
-			}
-			catch (StackTooDeepException const&)
-			{
-				// This might happen if the opcode reconstruction is not as efficient
-				// as the hand-crafted code.
-			}
-
-			if (shouldReplace)
-			{
-				copt << "Old size: " << (iter - orig) << ", new size: " << optItems.size();
-				count++;
-				for (auto moveIter = optItems.begin(); moveIter != optItems.end(); ++orig, ++moveIter)
-					*orig = move(*moveIter);
-				iter = m_items.erase(orig, iter);
+				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.
+					}
+
+					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);
 		}
 	}
 
@@ -461,7 +452,8 @@ bytes Assembly::assemble() const
 	for (auto const& i: tagRef)
 	{
 		bytesRef r(ret.data() + i.first, bytesPerTag);
-		toBigEndian(tagPos[i.second], r);
+		//@todo in the failure case, we could use the position of the invalid jumpdest
+		toBigEndian(i.second < tagPos.size() ? tagPos[i.second] : (1 << (8 * bytesPerTag)) - 1, r);
 	}
 
 	if (!m_data.empty())

libevmasm/CommonSubexpressionEliminator.cpp

@@ -45,16 +45,22 @@ vector<AssemblyItem> CommonSubexpressionEliminator::getOptimizedItems()
 	for (int height = minHeight; height <= m_state.stackHeight(); ++height)
 		targetStackContents[height] = m_state.stackElement(height, SourceLocation());
 
-	// Debug info:
-	//stream(cout, initialStackContents, targetStackContents);
-
 	AssemblyItems items = CSECodeGenerator(m_state.expressionClasses(), m_storeOperations).generateCode(
 		m_initialState.stackHeight(),
 		initialStackContents,
 		targetStackContents
 	);
 	if (m_breakingItem)
+	{
 		items.push_back(*m_breakingItem);
+		m_state.feedItem(*m_breakingItem);
+	}
+
+	// cleanup
+	m_initialState = m_state;
+	m_breakingItem = nullptr;
+	m_storeOperations.clear();
+
 	return items;
 }
 
@@ -113,16 +119,14 @@ AssemblyItems CSECodeGenerator::generateCode(
 {
 	m_stackHeight = _initialStackHeight;
 	m_stack = _initialStack;
+	m_targetStack = _targetStackContents;
 	for (auto const& item: m_stack)
-		if (!m_classPositions.count(item.second))
-			m_classPositions[item.second] = item.first;
-
-	// @todo: provide information about the positions of copies of class elements
+		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: _targetStackContents)
+	for (auto const& targetItem: m_targetStack)
 	{
 		m_finalClasses.insert(targetItem.second);
 		addDependencies(targetItem.second);
@@ -141,13 +145,16 @@ AssemblyItems CSECodeGenerator::generateCode(
 			generateClassElement(seqAndId.second, true);
 
 	// generate the target stack elements
-	for (auto const& targetItem: _targetStackContents)
+	for (auto const& targetItem: m_targetStack)
 	{
-		int position = generateClassElement(targetItem.second);
-		assertThrow(position != c_invalidPosition, OptimizerException, "");
-		if (position == targetItem.first)
+		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 const& location = m_expressionClasses.representative(targetItem.second).item->getLocation();
+		int position = classElementPosition(targetItem.second);
 		if (position < targetItem.first)
 			// it is already at its target, we need another copy
 			appendDup(position, location);
@@ -164,21 +171,24 @@ AssemblyItems CSECodeGenerator::generateCode(
 
 	// check validity
 	int finalHeight = 0;
-	if (!_targetStackContents.empty())
+	if (!m_targetStack.empty())
 		// have target stack, so its height should be the final height
-		finalHeight = (--_targetStackContents.end())->first;
+		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 = 0;
+		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);
@@ -254,19 +264,23 @@ void CSECodeGenerator::addDependencies(Id _c)
 	}
 }
 
-int CSECodeGenerator::generateClassElement(Id _c, bool _allowSequenced)
+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] != c_invalidPosition,
+			!m_classPositions[_c].empty(),
 			OptimizerException,
 			"Element already removed but still needed."
 		);
-		return m_classPositions[_c];
+		return;
 	}
 	ExpressionClasses::Expression const& expr = m_expressionClasses.representative(_c);
 	assertThrow(
@@ -339,16 +353,16 @@ int CSECodeGenerator::generateClassElement(Id _c, bool _allowSequenced)
 			m_generatedItems.back() == AssemblyItem(Instruction::SWAP1))
 		// this will not append a swap but remove the one that is already there
 		appendOrRemoveSwap(m_stackHeight - 1, location);
-	for (auto arg: arguments)
-		if (canBeRemoved(arg, _c))
-			m_classPositions[arg] = c_invalidPosition;
 	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;
-		return m_classPositions[_c] = m_stackHeight;
+		m_classPositions[_c].insert(m_stackHeight);
 	}
 	else
 	{
@@ -357,31 +371,39 @@ int CSECodeGenerator::generateClassElement(Id _c, bool _allowSequenced)
 			OptimizerException,
 			"Invalid number of return values."
 		);
-		return m_classPositions[_c] = c_invalidPosition;
+		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) != c_invalidPosition,
+		m_classPositions.count(_id) && !m_classPositions.at(_id).empty(),
 		OptimizerException,
 		"Element requested but is not present."
 	);
-	return m_classPositions.at(_id);
+	return *max_element(m_classPositions.at(_id).begin(), m_classPositions.at(_id).end());
 }
 
-bool CSECodeGenerator::canBeRemoved(Id _element, Id _result)
+bool CSECodeGenerator::canBeRemoved(Id _element, Id _result, int _fromPosition)
 {
-	// Returns false if _element is finally needed or is needed by a class that has not been
-	// computed yet. Note that m_classPositions also includes classes that were deleted in the meantime.
-	if (m_finalClasses.count(_element))
-		return false;
+	// Default for _fromPosition is the canonical position of the element.
+	if (_fromPosition == c_invalidPosition)
+		_fromPosition = classElementPosition(_element);
 
-	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;
+	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;
 }
 
@@ -391,11 +413,11 @@ bool CSECodeGenerator::removeStackTopIfPossible()
 		return false;
 	assertThrow(m_stack.count(m_stackHeight) > 0, OptimizerException, "");
 	Id top = m_stack[m_stackHeight];
-	if (!canBeRemoved(top))
+	if (!canBeRemoved(top, Id(-1), m_stackHeight))
 		return false;
-	m_generatedItems.push_back(AssemblyItem(Instruction::POP));
+	m_classPositions[m_stack[m_stackHeight]].erase(m_stackHeight);
 	m_stack.erase(m_stackHeight);
-	m_stackHeight--;
+	appendItem(AssemblyItem(Instruction::POP));
 	return true;
 }
 
@@ -407,6 +429,7 @@ void CSECodeGenerator::appendDup(int _fromPosition, SourceLocation const& _locat
 	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)
@@ -418,13 +441,15 @@ void CSECodeGenerator::appendOrRemoveSwap(int _fromPosition, SourceLocation cons
 	assertThrow(instructionNum <= 16, StackTooDeepException, "Stack too deep.");
 	assertThrow(1 <= instructionNum, OptimizerException, "Invalid stack access.");
 	appendItem(AssemblyItem(swapInstruction(instructionNum), _location));
-	// The value of a class can be present in multiple locations on the stack. We only update the
-	// "canonical" one that is tracked by m_classPositions
-	if (m_classPositions[m_stack[m_stackHeight]] == m_stackHeight)
-		m_classPositions[m_stack[m_stackHeight]] = _fromPosition;
-	if (m_classPositions[m_stack[_fromPosition]] == _fromPosition)
-		m_classPositions[m_stack[_fromPosition]] = m_stackHeight;
-	swap(m_stack[m_stackHeight], m_stack[_fromPosition]);
+
+	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())

libevmasm/CommonSubexpressionEliminator.h

@@ -71,13 +71,6 @@ public:
 	/// @returns the resulting items after optimization.
 	AssemblyItems getOptimizedItems();
 
-	/// Streams debugging information to @a _out.
-	std::ostream& stream(
-		std::ostream& _out,
-		std::map<int, Id> _initialStack = std::map<int, Id>(),
-		std::map<int, Id> _targetStack = std::map<int, Id>()
-	) const;
-
 private:
 	/// Feeds the item into the system for analysis.
 	void feedItem(AssemblyItem const& _item, bool _copyItem = false);
@@ -126,16 +119,15 @@ private:
 	void addDependencies(Id _c);
 
 	/// Produce code that generates the given element if it is not yet present.
-	/// @returns the stack position of the element or c_invalidPosition if it does not actually
-	/// generate a value on the stack.
 	/// @param _allowSequenced indicates that sequence-constrained operations are allowed
-	int generateClassElement(Id _c, bool _allowSequenced = false);
+	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 @a _element can be removed - in general or, if given, while computing @a _result.
-	bool canBeRemoved(Id _element, Id _result = Id(-1));
+	/// @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();
@@ -157,8 +149,8 @@ private:
 	std::multimap<Id, Id> m_neededBy;
 	/// Current content of the stack.
 	std::map<int, Id> m_stack;
-	/// Current positions of equivalence classes, equal to c_invalidPosition if already deleted.
-	std::map<Id, int> m_classPositions;
+	/// 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;
@@ -167,6 +159,7 @@ private:
 	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>
@@ -175,6 +168,7 @@ _AssemblyItemIterator CommonSubexpressionEliminator::feedItems(
 	_AssemblyItemIterator _end
 )
 {
+	assertThrow(!m_breakingItem, OptimizerException, "Invalid use of CommonSubexpressionEliminator.");
 	for (; _iterator != _end && !SemanticInformation::breaksCSEAnalysisBlock(*_iterator); ++_iterator)
 		feedItem(*_iterator);
 	if (_iterator != _end)

libevmasm/ControlFlowGraph.cpp

@@ -142,7 +142,7 @@ void ControlFlowGraph::removeUnusedBlocks()
 		BasicBlock const& block = m_blocks.at(blocksToProcess.back());
 		blocksToProcess.pop_back();
 		for (BlockId tag: block.pushedTags)
-			if (!neededBlocks.count(tag))
+			if (!neededBlocks.count(tag) && m_blocks.count(tag))
 			{
 				neededBlocks.insert(tag);
 				blocksToProcess.push_back(tag);
@@ -191,12 +191,12 @@ void ControlFlowGraph::setPrevLinks()
 		if (push.type() != PushTag)
 			continue;
 		BlockId nextId(push.data());
-		if (m_blocks.at(nextId).prev)
+		if (m_blocks.count(nextId) && m_blocks.at(nextId).prev)
 			continue;
 		bool hasLoop = false;
-		for (BlockId id = nextId; id && !hasLoop; id = m_blocks.at(id).next)
+		for (BlockId id = nextId; id && m_blocks.count(id) && !hasLoop; id = m_blocks.at(id).next)
 			hasLoop = (id == blockId);
-		if (hasLoop)
+		if (hasLoop || !m_blocks.count(nextId))
 			continue;
 
 		m_blocks[nextId].prev = blockId;
@@ -225,6 +225,8 @@ void ControlFlowGraph::gatherKnowledge()
 	{
 		//@todo we might have to do something like incrementing the sequence number for each JUMPDEST
 		assertThrow(!!workQueue.back().first, OptimizerException, "");
+		if (!m_blocks.count(workQueue.back().first))
+			continue; // too bad, we do not know the tag, probably an invalid jump
 		BasicBlock& block = m_blocks.at(workQueue.back().first);
 		KnownStatePointer state = workQueue.back().second;
 		workQueue.pop_back();
@@ -281,6 +283,15 @@ void ControlFlowGraph::gatherKnowledge()
 		)
 			workQueue.push_back(make_pair(block.next, state->copy()));
 	}
+
+	// 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()
@@ -288,7 +299,8 @@ BasicBlocks ControlFlowGraph::rebuildCode()
 	map<BlockId, unsigned> pushes;
 	for (auto& idAndBlock: m_blocks)
 		for (BlockId ref: idAndBlock.second.pushedTags)
-			pushes[ref]++;
+			if (m_blocks.count(ref))
+				pushes[ref]++;
 
 	set<BlockId> blocksToAdd;
 	for (auto it: m_blocks)

libevmasm/KnownState.cpp

@@ -160,23 +160,51 @@ KnownState::StoreOperation KnownState::feedItem(AssemblyItem const& _item, bool
 	return op;
 }
 
-void KnownState::reduceToCommonKnowledge(KnownState const& /*_other*/)
+/// Helper function for KnownState::reduceToCommonKnowledge, removes everything from
+/// _this which is not in or not equal to the value in _other.
+template <class _Mapping, class _KeyType> void intersect(
+	_Mapping& _this,
+	_Mapping const& _other,
+	function<_KeyType(_KeyType)> const& _keyTrans = [](_KeyType _k) { return _k; }
+)
+{
+	for (auto it = _this.begin(); it != _this.end();)
+		if (_other.count(_keyTrans(it->first)) && _other.at(_keyTrans(it->first)) == it->second)
+			++it;
+		else
+			it = _this.erase(it);
+}
+
+template <class _Mapping> void intersect(_Mapping& _this, _Mapping const& _other)
 {
-	//@todo
-	*this = KnownState(m_expressionClasses);
+	intersect<_Mapping, ExpressionClasses::Id>(_this, _other, [](ExpressionClasses::Id _k) { return _k; });
+}
+
+void KnownState::reduceToCommonKnowledge(KnownState const& _other)
+{
+	int stackDiff = m_stackHeight - _other.m_stackHeight;
+	function<int(int)> stackKeyTransform = [=](int _key) -> int { return _key - stackDiff; };
+	intersect(m_stackElements, _other.m_stackElements, stackKeyTransform);
+	// 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);
 }
 
 bool KnownState::operator==(const KnownState& _other) const
 {
-	//@todo
-	return (
-		m_stackElements.empty() &&
-		_other.m_stackElements.empty() &&
-		m_storageContent.empty() &&
-		_other.m_storageContent.empty() &&
-		m_memoryContent.empty() &&
-		_other.m_memoryContent.empty()
-	);
+	return m_storageContent == _other.m_storageContent &&
+		m_memoryContent == _other.m_memoryContent &&
+		m_stackHeight == _other.m_stackHeight &&
+		m_stackElements == _other.m_stackElements;
 }
 
 ExpressionClasses::Id KnownState::stackElement(int _stackHeight, SourceLocation const& _location)

test/libsolidity/SolidityOptimizer.cpp

@@ -251,6 +251,63 @@ BOOST_AUTO_TEST_CASE(function_calls)
 	compareVersions("f(uint256)", 36);
 }
 
+BOOST_AUTO_TEST_CASE(storage_write_in_loops)
+{
+	char const* sourceCode = R"(
+		contract test {
+			uint d;
+			function f(uint a) returns (uint r) {
+				var x = d;
+				for (uint i = 1; i < a * a; i++) {
+					r = d;
+					d = i;
+				}
+
+			}
+		}
+	)";
+	compileBothVersions(sourceCode);
+	compareVersions("f(uint256)", 0);
+	compareVersions("f(uint256)", 10);
+	compareVersions("f(uint256)", 36);
+}
+
+BOOST_AUTO_TEST_CASE(retain_information_in_branches)
+{
+	// This tests that the optimizer knows that we already have "z == sha3(y)" inside both branches.
+	char const* sourceCode = R"(
+		contract c {
+			bytes32 d;
+			uint a;
+			function f(uint x, bytes32 y) returns (uint r_a, bytes32 r_d) {
+				bytes32 z = sha3(y);
+				if (x > 8) {
+					z = sha3(y);
+					a = x;
+				} else {
+					z = sha3(y);
+					a = x;
+				}
+				r_a = a;
+				r_d = d;
+			}
+		}
+	)";
+	compileBothVersions(sourceCode);
+	compareVersions("f(uint256,bytes32)", 0, "abc");
+	compareVersions("f(uint256,bytes32)", 8, "def");
+	compareVersions("f(uint256,bytes32)", 10, "ghi");
+
+	m_optimize = true;
+	bytes optimizedBytecode = compileAndRun(sourceCode, 0, "c");
+	size_t numSHA3s = 0;
+	eth::eachInstruction(optimizedBytecode, [&](Instruction _instr, u256 const&) {
+		if (_instr == eth::Instruction::SHA3)
+			numSHA3s++;
+	});
+	BOOST_CHECK_EQUAL(1, numSHA3s);
+}
+
 BOOST_AUTO_TEST_CASE(cse_intermediate_swap)
 {
 	eth::KnownState state;