Better gas meter implementation for swaps and dups.

Author: ekpyron

libevmasm/GasMeter.cpp

@@ -263,12 +263,11 @@ GasMeter::GasConsumption GasMeter::memoryGas(int _stackPosOffset, int _stackPosS
 		}));
 }
 
-unsigned GasMeter::runGas(Instruction _instruction, langutil::EVMVersion _evmVersion)
+namespace
 {
-	if (_instruction == Instruction::JUMPDEST)
-		return 1;
-
-	switch (instructionInfo(_instruction, _evmVersion).gasPriceTier)
+std::optional<unsigned> gasCostForTier(Tier _tier)
+{
+	switch (_tier)
 	{
 	case Tier::Zero:        return GasCosts::tier0Gas;
 	case Tier::Base:        return GasCosts::tier1Gas;
@@ -286,10 +285,21 @@ unsigned GasMeter::runGas(Instruction _instruction, langutil::EVMVersion _evmVer
 
 	case Tier::Special:
 	case Tier::Invalid:
-		assertThrow(false, OptimizerException, "Invalid gas tier for instruction " + instructionInfo(_instruction, _evmVersion).name);
+		return std::nullopt;
 	}
 	util::unreachable();
 }
+}
+
+unsigned GasMeter::runGas(Instruction _instruction, langutil::EVMVersion _evmVersion)
+{
+	if (_instruction == Instruction::JUMPDEST)
+		return 1;
+
+	if (auto gasCost = gasCostForTier(instructionInfo(_instruction, _evmVersion).gasPriceTier))
+		return *gasCost;
+	assertThrow(false, OptimizerException, "Invalid gas tier for instruction " + instructionInfo(_instruction, _evmVersion).name);
+}
 
 unsigned GasMeter::pushGas(u256 _value, langutil::EVMVersion _evmVersion)
 {
@@ -299,14 +309,22 @@ unsigned GasMeter::pushGas(u256 _value, langutil::EVMVersion _evmVersion)
 	);
 }
 
-unsigned GasMeter::swapGas(size_t)
+unsigned GasMeter::swapGas(size_t _depth, langutil::EVMVersion _evmVersion)
 {
-	return 3;
+	if (_depth <= 16)
+		return runGas(evmasm::swapInstruction(static_cast<unsigned>(_depth)), _evmVersion);
+	auto gasCost = gasCostForTier(instructionInfo(evmasm::Instruction::SWAPN, _evmVersion).gasPriceTier);
+	assertThrow(gasCost.has_value(), OptimizerException, "Expected gas cost for SWAPN to be defined.");
+	return *gasCost;
 }
 
-unsigned GasMeter::dupGas(size_t)
+unsigned GasMeter::dupGas(size_t _depth, langutil::EVMVersion _evmVersion)
 {
-	return 3;
+	if (_depth <= 16)
+		return runGas(evmasm::swapInstruction(static_cast<unsigned>(_depth)), _evmVersion);
+	auto gasCost = gasCostForTier(instructionInfo(evmasm::Instruction::DUPN, _evmVersion).gasPriceTier);
+	assertThrow(gasCost.has_value(), OptimizerException, "Expected gas cost for DUPN to be defined.");
+	return *gasCost;
 }
 
 u256 GasMeter::dataGas(bytes const& _data, bool _inCreation, langutil::EVMVersion _evmVersion)

libevmasm/GasMeter.h

@@ -229,11 +229,11 @@ class GasMeter
 	/// @returns gas costs for push instructions (may change depending on EVM version)
 	static unsigned pushGas(u256 _value, langutil::EVMVersion _evmVersion);
 
-	/// @returns gas costs for swap instructions
-	static unsigned swapGas(size_t _depth);
+	/// @returns gas costs for swap instructions (may change depending on EVM version)
+	static unsigned swapGas(size_t _depth, langutil::EVMVersion _evmVersion);
 
-	/// @returns gas costs for dup instructions
-	static unsigned dupGas(size_t _depth);
+	/// @returns gas costs for dup instructions (may change depending on EVM version)
+	static unsigned dupGas(size_t _depth, langutil::EVMVersion _evmVersion);
 
 	/// @returns the gas cost of the supplied data, depending whether it is in creation code, or not.
 	/// In case of @a _inCreation, the data is only sent as a transaction and is not stored, whereas

libyul/backends/evm/StackLayoutGenerator.cpp

@@ -782,7 +782,7 @@ void StackLayoutGenerator::fillInJunk(CFG::BasicBlock const& _block, CFG::Functi
 			if (_swapDepth > m_reachableStackDepth)
 				opGas += 1000;
 			else
-				opGas += evmasm::GasMeter::swapGas(_swapDepth);
+				opGas += evmasm::GasMeter::swapGas(_swapDepth, langutil::EVMVersion{});
 		};
 		auto dupOrPush = [&](StackSlot const& _slot)
 		{
@@ -793,7 +793,7 @@ void StackLayoutGenerator::fillInJunk(CFG::BasicBlock const& _block, CFG::Functi
 				if (auto depth = util::findOffset(_source | ranges::views::reverse, _slot))
 				{
 					if (*depth < m_reachableStackDepth)
-						opGas += evmasm::GasMeter::dupGas(*depth + 1);
+						opGas += evmasm::GasMeter::dupGas(*depth + 1, langutil::EVMVersion{});
 					else
 						opGas += 1000;
 				}