SHA3 optimizations.

libevmcore/CMakeLists.txt

@@ -25,6 +25,7 @@ else()
 endif()
 
 target_link_libraries(${EXECUTABLE} devcore)
+target_link_libraries(${EXECUTABLE} devcrypto)
 
 install( TARGETS ${EXECUTABLE} RUNTIME DESTINATION bin ARCHIVE DESTINATION lib LIBRARY DESTINATION lib )
 install( FILES ${HEADERS} DESTINATION include/${EXECUTABLE} )

libevmcore/CommonSubexpressionEliminator.cpp

@@ -23,6 +23,7 @@
 
 #include <functional>
 #include <boost/range/adaptor/reversed.hpp>
+#include <libdevcrypto/SHA3.h>
 #include <libevmcore/CommonSubexpressionEliminator.h>
 #include <libevmcore/AssemblyItem.h>
 
@@ -130,6 +131,8 @@ void CommonSubexpressionEliminator::feedItem(AssemblyItem const& _item, bool _co
 				storeInMemory(arguments[0], arguments[1]);
 			else if (_item.instruction() == Instruction::MLOAD)
 				setStackElement(m_stackHeight + _item.deposit(), loadFromMemory(arguments[0]));
+			else if (_item.instruction() == Instruction::SHA3)
+				setStackElement(m_stackHeight + _item.deposit(), applySha3(arguments.at(0), arguments.at(1)));
 			else
 				setStackElement(m_stackHeight + _item.deposit(), m_expressionClasses.find(_item, arguments, _copyItem));
 		}
@@ -200,9 +203,10 @@ void CommonSubexpressionEliminator::storeInStorage(Id _slot, Id _value)
 		return;
 	m_sequenceNumber++;
 	decltype(m_storageContent) storageContents;
-	// copy over values at points where we know that they are different from _slot
+	// copy over values at points where we know that they are different from _slot or that we know
+	// that the value is equal
 	for (auto const& storageItem: m_storageContent)
-		if (m_expressionClasses.knownToBeDifferent(storageItem.first, _slot))
+		if (m_expressionClasses.knownToBeDifferent(storageItem.first, _slot) || storageItem.second == _value)
 			storageContents.insert(storageItem);
 	m_storageContent = move(storageContents);
 	Id id = m_expressionClasses.find(Instruction::SSTORE, {_slot, _value}, true, m_sequenceNumber);
@@ -247,6 +251,37 @@ ExpressionClasses::Id CommonSubexpressionEliminator::loadFromMemory(Id _slot)
 		return m_memoryContent[_slot] = m_expressionClasses.find(Instruction::MLOAD, {_slot}, true, m_sequenceNumber);
 }
 
+CommonSubexpressionEliminator::Id CommonSubexpressionEliminator::applySha3(Id _start, Id _length)
+{
+	// 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(Instruction::SHA3, {_start, _length}, true, m_sequenceNumber);
+
+	vector<Id> arguments;
+	for (u256 i = 0; i < *l; i += 32)
+	{
+		Id slot = m_expressionClasses.find(Instruction::ADD, {_start, m_expressionClasses.find(i)});
+		arguments.push_back(loadFromMemory(slot));
+	}
+	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(u256(sha3(data)));
+	}
+	else
+		v = m_expressionClasses.find(Instruction::SHA3, {_start, _length}, true, m_sequenceNumber);
+	return m_knownSha3Hashes[arguments] = v;
+}
+
 CSECodeGenerator::CSECodeGenerator(
 	ExpressionClasses& _expressionClasses,
 	vector<CSECodeGenerator::StoreOperation> const& _storeOperations
@@ -338,7 +373,8 @@ void CSECodeGenerator::addDependencies(Id _c)
 	}
 	if (expr.item->type() == Operation && (
 		expr.item->instruction() == Instruction::SLOAD ||
-		expr.item->instruction() == Instruction::MLOAD
+		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
@@ -355,11 +391,41 @@ void CSECodeGenerator::addDependencies(Id _c)
 			StoreOperations const& storeOps = p.second;
 			if (storeOps.front().sequenceNumber > expr.sequenceNumber)
 				continue;
-			if (
-				(target == StoreOperation::Memory && m_expressionClasses.knownToBeDifferentBy32(slot, slotToLoadFrom)) ||
-				(target == StoreOperation::Storage && m_expressionClasses.knownToBeDifferent(slot, slotToLoadFrom))
-			)
+			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);
+				Id offsetToStart = m_expressionClasses.find(Instruction::SUB, {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)

libevmcore/CommonSubexpressionEliminator.h

@@ -117,6 +117,8 @@ private:
 	void storeInMemory(Id _slot, Id _value);
 	/// Retrieves the current value at the given slot in memory or creates a new special mload class.
 	Id loadFromMemory(Id _slot);
+	/// Finds or creates a new expression that applies the sha3 hash function to the contents in memory.
+	Id applySha3(Id _start, Id _length);
 
 	/// Current stack height, can be negative.
 	int m_stackHeight = 0;
@@ -129,6 +131,8 @@ private:
 	/// 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;
 	/// Keeps information about which storage or memory slots were written to at which sequence
 	/// number with what instruction.
 	std::vector<StoreOperation> m_storeOperations;

libevmcore/SemanticInformation.cpp

@@ -52,8 +52,6 @@ bool SemanticInformation::breaksCSEAnalysisBlock(AssemblyItem const& _item)
 			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
-		if (_item.instruction() == Instruction::SHA3)
-			return true; //@todo: we have to compare sha3's not based on their memory addresses but on the memory content.
 		InstructionInfo info = instructionInfo(_item.instruction());
 		if (_item.instruction() == Instruction::SSTORE)
 			return false;

libsolidity/CMakeLists.txt

@@ -27,7 +27,6 @@ endif()
 
 target_link_libraries(${EXECUTABLE} ${JSONCPP_LIBRARIES})
 target_link_libraries(${EXECUTABLE} evmcore)
-target_link_libraries(${EXECUTABLE} devcore)
 target_link_libraries(${EXECUTABLE} devcrypto)
 
 install( TARGETS ${EXECUTABLE} RUNTIME DESTINATION bin ARCHIVE DESTINATION lib LIBRARY DESTINATION lib )

test/SolidityOptimizer.cpp

@@ -56,8 +56,16 @@ public:
 		m_nonOptimizedContract = m_contractAddress;
 		m_optimize = true;
 		bytes optimizedBytecode = compileAndRun(_sourceCode, _value, _contractName);
+		size_t nonOptimizedSize = 0;
+		eth::eachInstruction(nonOptimizedBytecode, [&](Instruction, u256 const&) {
+			nonOptimizedSize++;
+		});
+		size_t optimizedSize = 0;
+		eth::eachInstruction(optimizedBytecode, [&](Instruction, u256 const&) {
+			optimizedSize++;
+		});
 		BOOST_CHECK_MESSAGE(
-			nonOptimizedBytecode.size() > optimizedBytecode.size(),
+			nonOptimizedSize > optimizedSize,
 			"Optimizer did not reduce bytecode size."
 		);
 		m_optimizedContract = m_contractAddress;
@@ -75,11 +83,16 @@ public:
 							"\nOptimized:     " + toHex(optimizedOutput));
 	}
 
-	void checkCSE(AssemblyItems const& _input, AssemblyItems const& _expectation)
+	AssemblyItems getCSE(AssemblyItems const& _input)
 	{
 		eth::CommonSubexpressionEliminator cse;
 		BOOST_REQUIRE(cse.feedItems(_input.begin(), _input.end()) == _input.end());
-		AssemblyItems output = cse.getOptimizedItems();
+		return cse.getOptimizedItems();
+	}
+
+	void checkCSE(AssemblyItems const& _input, AssemblyItems const& _expectation)
+	{
+		AssemblyItems output = getCSE(_input);
 		BOOST_CHECK_EQUAL_COLLECTIONS(_expectation.begin(), _expectation.end(), output.begin(), output.end());
 	}
 
@@ -569,6 +582,155 @@ BOOST_AUTO_TEST_CASE(cse_jumpi_jump)
 	});
 }
 
+BOOST_AUTO_TEST_CASE(cse_empty_sha3)
+{
+	AssemblyItems input{
+		u256(0),
+		Instruction::DUP2,
+		Instruction::SHA3
+	};
+	checkCSE(input, {
+		u256(sha3(bytesConstRef()))
+	});
+}
+
+BOOST_AUTO_TEST_CASE(cse_partial_sha3)
+{
+	AssemblyItems input{
+		u256(0xabcd) << (256 - 16),
+		u256(0),
+		Instruction::MSTORE,
+		u256(2),
+		u256(0),
+		Instruction::SHA3
+	};
+	checkCSE(input, {
+		u256(0xabcd) << (256 - 16),
+		u256(0),
+		Instruction::MSTORE,
+		u256(sha3(bytes{0xab, 0xcd}))
+	});
+}
+
+BOOST_AUTO_TEST_CASE(cse_sha3_twice_same_location)
+{
+	// sha3 twice from same dynamic location
+	AssemblyItems input{
+		Instruction::DUP2,
+		Instruction::DUP1,
+		Instruction::MSTORE,
+		u256(64),
+		Instruction::DUP2,
+		Instruction::SHA3,
+		u256(64),
+		Instruction::DUP3,
+		Instruction::SHA3
+	};
+	checkCSE(input, {
+		Instruction::DUP2,
+		Instruction::DUP1,
+		Instruction::MSTORE,
+		u256(64),
+		Instruction::DUP2,
+		Instruction::SHA3,
+		Instruction::DUP1
+	});
+}
+
+BOOST_AUTO_TEST_CASE(cse_sha3_twice_same_content)
+{
+	// sha3 twice from different dynamic location but with same content
+	AssemblyItems input{
+		Instruction::DUP1,
+		u256(0x80),
+		Instruction::MSTORE, // m[128] = DUP1
+		u256(0x20),
+		u256(0x80),
+		Instruction::SHA3, // sha3(m[128..(128+32)])
+		Instruction::DUP2,
+		u256(12),
+		Instruction::MSTORE, // m[12] = DUP1
+		u256(0x20),
+		u256(12),
+		Instruction::SHA3 // sha3(m[12..(12+32)])
+	};
+	checkCSE(input, {
+		u256(0x80),
+		Instruction::DUP2,
+		Instruction::DUP2,
+		Instruction::MSTORE,
+		u256(0x20),
+		Instruction::SWAP1,
+		Instruction::SHA3,
+		u256(12),
+		Instruction::DUP3,
+		Instruction::SWAP1,
+		Instruction::MSTORE,
+		Instruction::DUP1
+	});
+}
+
+BOOST_AUTO_TEST_CASE(cse_sha3_twice_same_content_dynamic_store_in_between)
+{
+	// sha3 twice from different dynamic location but with same content,
+	// dynamic mstore in between, which forces us to re-calculate the sha3
+	AssemblyItems input{
+		u256(0x80),
+		Instruction::DUP2,
+		Instruction::DUP2,
+		Instruction::MSTORE, // m[128] = DUP1
+		u256(0x20),
+		Instruction::DUP1,
+		Instruction::DUP3,
+		Instruction::SHA3, // sha3(m[128..(128+32)])
+		u256(12),
+		Instruction::DUP5,
+		Instruction::DUP2,
+		Instruction::MSTORE, // m[12] = DUP1
+		Instruction::DUP12,
+		Instruction::DUP14,
+		Instruction::MSTORE, // destroys memory knowledge
+		Instruction::SWAP2,
+		Instruction::SWAP1,
+		Instruction::SWAP2,
+		Instruction::SHA3 // sha3(m[12..(12+32)])
+	};
+	checkCSE(input, input);
+}
+
+BOOST_AUTO_TEST_CASE(cse_sha3_twice_same_content_noninterfering_store_in_between)
+{
+	// sha3 twice from different dynamic location but with same content,
+	// dynamic mstore in between, but does not force us to re-calculate the sha3
+	AssemblyItems input{
+		u256(0x80),
+		Instruction::DUP2,
+		Instruction::DUP2,
+		Instruction::MSTORE, // m[128] = DUP1
+		u256(0x20),
+		Instruction::DUP1,
+		Instruction::DUP3,
+		Instruction::SHA3, // sha3(m[128..(128+32)])
+		u256(12),
+		Instruction::DUP5,
+		Instruction::DUP2,
+		Instruction::MSTORE, // m[12] = DUP1
+				Instruction::DUP12,
+				u256(12 + 32),
+				Instruction::MSTORE, // does not destoy memory knowledge
+				Instruction::DUP13,
+				u256(128 - 32),
+				Instruction::MSTORE, // does not destoy memory knowledge
+				u256(0x20),
+				u256(12),
+				Instruction::SHA3 // sha3(m[12..(12+32)])
+	};
+	// if this changes too often, only count the number of SHA3 and MSTORE instructions
+	AssemblyItems output = getCSE(input);
+	BOOST_CHECK_EQUAL(4, count(output.begin(), output.end(), AssemblyItem(Instruction::MSTORE)));
+	BOOST_CHECK_EQUAL(1, count(output.begin(), output.end(), AssemblyItem(Instruction::SHA3)));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }