Merge pull request #8246 from ethereum/yul-codegen-trycatch

Sol-to-Yul codegen for try-catch statement

libsolidity/CMakeLists.txt

@@ -75,6 +75,8 @@ set(sources
 	codegen/LValue.h
 	codegen/MultiUseYulFunctionCollector.h
 	codegen/MultiUseYulFunctionCollector.cpp
+	codegen/ReturnInfo.h
+	codegen/ReturnInfo.cpp
 	codegen/YulUtilFunctions.h
 	codegen/YulUtilFunctions.cpp
 	codegen/ir/IRGenerator.cpp

libsolidity/ast/AST.cpp

@@ -756,3 +756,25 @@ string Literal::getChecksummedAddress() const
 	address.insert(address.begin(), 40 - address.size(), '0');
 	return util::getChecksummedAddress(address);
 }
+
+TryCatchClause const* TryStatement::successClause() const
+{
+	solAssert(m_clauses.size() > 0, "");
+	return m_clauses[0].get();
+}
+
+TryCatchClause const* TryStatement::structuredClause() const
+{
+	for (size_t i = 1; i < m_clauses.size(); ++i)
+		if (m_clauses[i]->errorName() == "Error")
+			return m_clauses[i].get();
+	return nullptr;
+}
+
+TryCatchClause const* TryStatement::fallbackClause() const
+{
+	for (size_t i = 1; i < m_clauses.size(); ++i)
+		if (m_clauses[i]->errorName().empty())
+			return m_clauses[i].get();
+	return nullptr;
+}

libsolidity/ast/AST.h

@@ -1451,6 +1451,10 @@ public:
 	Expression const& externalCall() const { return *m_externalCall; }
 	std::vector<ASTPointer<TryCatchClause>> const& clauses() const { return m_clauses; }
 
+	TryCatchClause const* successClause() const;
+	TryCatchClause const* structuredClause() const;
+	TryCatchClause const* fallbackClause() const;
+
 private:
 	ASTPointer<Expression> m_externalCall;
 	std::vector<ASTPointer<TryCatchClause>> m_clauses;

libsolidity/codegen/ContractCompiler.cpp

@@ -949,43 +949,7 @@ void ContractCompiler::handleCatch(vector<ASTPointer<TryCatchClause>> const& _ca
 
 		// Try to decode the error message.
 		// If this fails, leaves 0 on the stack, otherwise the pointer to the data string.
-		m_context << u256(0);
-		m_context.appendInlineAssembly(
-			util::Whiskers(R"({
-				data := mload(0x40)
-				mstore(data, 0)
-				for {} 1 {} {
-					if lt(returndatasize(), 0x44) { data := 0 break }
-					returndatacopy(0, 0, 4)
-					let sig := <getSig>
-					if iszero(eq(sig, 0x<ErrorSignature>)) { data := 0 break }
-					returndatacopy(data, 4, sub(returndatasize(), 4))
-					let offset := mload(data)
-					if or(
-						gt(offset, 0xffffffffffffffff),
-						gt(add(offset, 0x24), returndatasize())
-					) {
-						data := 0
-						break
-					}
-					let msg := add(data, offset)
-					let length := mload(msg)
-					if gt(length, 0xffffffffffffffff) { data := 0 break }
-					let end := add(add(msg, 0x20), length)
-					if gt(end, add(data, returndatasize())) { data := 0 break }
-					mstore(0x40, and(add(end, 0x1f), not(0x1f)))
-					data := msg
-					break
-				}
-			})")
-			("ErrorSignature", errorHash)
-			("getSig",
-				m_context.evmVersion().hasBitwiseShifting() ?
-				"shr(224, mload(0))" :
-				"div(mload(0), " + (u256(1) << 224).str() + ")"
-			).render(),
-			{"data"}
-		);
+		m_context.callYulFunction(m_context.utilFunctions().tryDecodeErrorMessageFunction(), 0, 1);
 		m_context << Instruction::DUP1;
 		AssemblyItem decodeSuccessTag = m_context.appendConditionalJump();
 		m_context << Instruction::POP;

libsolidity/codegen/ExpressionCompiler.cpp

@@ -22,12 +22,14 @@
 
 #include <libsolidity/codegen/ExpressionCompiler.h>
 
-#include <libsolidity/ast/AST.h>
-#include <libsolidity/ast/TypeProvider.h>
+#include <libsolidity/codegen/ReturnInfo.h>
 #include <libsolidity/codegen/CompilerContext.h>
 #include <libsolidity/codegen/CompilerUtils.h>
 #include <libsolidity/codegen/LValue.h>
 
+#include <libsolidity/ast/AST.h>
+#include <libsolidity/ast/TypeProvider.h>
+
 #include <libevmasm/GasMeter.h>
 #include <libsolutil/Common.h>
 #include <libsolutil/Keccak256.h>
@@ -2185,30 +2187,11 @@ void ExpressionCompiler::appendExternalFunctionCall(
 		solAssert(!_functionType.isBareCall(), "");
 	}
 
-	bool haveReturndatacopy = m_context.evmVersion().supportsReturndata();
-	unsigned retSize = 0;
-	bool dynamicReturnSize = false;
-	TypePointers returnTypes;
-	if (!returnSuccessConditionAndReturndata)
-	{
-		if (haveReturndatacopy)
-			returnTypes = _functionType.returnParameterTypes();
-		else
-			returnTypes = _functionType.returnParameterTypesWithoutDynamicTypes();
-
-		for (auto const& retType: returnTypes)
-			if (retType->isDynamicallyEncoded())
-			{
-				solAssert(haveReturndatacopy, "");
-				dynamicReturnSize = true;
-				retSize = 0;
-				break;
-			}
-			else if (retType->decodingType())
-				retSize += retType->decodingType()->calldataEncodedSize();
-			else
-				retSize += retType->calldataEncodedSize();
-	}
+	ReturnInfo const returnInfo{m_context.evmVersion(), _functionType};
+	bool const haveReturndatacopy = m_context.evmVersion().supportsReturndata();
+	unsigned const retSize = returnInfo.estimatedReturnSize;
+	bool const dynamicReturnSize = returnInfo.dynamicReturnSize;
+	TypePointers const& returnTypes = returnInfo.returnTypes;
 
 	// Evaluate arguments.
 	TypePointers argumentTypes;

libsolidity/codegen/ReturnInfo.cpp

@@ -0,0 +1,55 @@
+/*
+	This file is part of solidity.
+
+	solidity 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.
+
+	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <libsolidity/codegen/ReturnInfo.h>
+
+#include <libsolidity/ast/Types.h>
+#include <libsolidity/ast/AST.h>
+
+using namespace solidity::frontend;
+using namespace solidity::langutil;
+
+ReturnInfo::ReturnInfo(EVMVersion const& _evmVersion, FunctionType const& _functionType)
+{
+	FunctionType::Kind const funKind = _functionType.kind();
+	bool const haveReturndatacopy = _evmVersion.supportsReturndata();
+	bool const returnSuccessConditionAndReturndata =
+		funKind == FunctionType::Kind::BareCall ||
+		funKind == FunctionType::Kind::BareDelegateCall ||
+		funKind == FunctionType::Kind::BareStaticCall;
+
+	if (!returnSuccessConditionAndReturndata)
+	{
+		if (haveReturndatacopy)
+			returnTypes = _functionType.returnParameterTypes();
+		else
+			returnTypes = _functionType.returnParameterTypesWithoutDynamicTypes();
+
+		for (auto const& retType: returnTypes)
+			if (retType->isDynamicallyEncoded())
+			{
+				solAssert(haveReturndatacopy, "");
+				dynamicReturnSize = true;
+				estimatedReturnSize = 0;
+				break;
+			}
+			else if (retType->decodingType())
+				estimatedReturnSize += retType->decodingType()->calldataEncodedSize();
+			else
+				estimatedReturnSize += retType->calldataEncodedSize();
+	}
+}

libsolidity/codegen/ReturnInfo.h

@@ -0,0 +1,47 @@
+/*
+	This file is part of solidity.
+
+	solidity 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.
+
+	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * Component that computes information relevant during decoding an external function
+ * call's return values.
+ */
+#pragma once
+
+#include <liblangutil/EVMVersion.h>
+#include <libsolidity/ast/Types.h>
+
+namespace solidity::frontend
+{
+
+/**
+ * Computes and holds information relevant during decoding an external function
+ * call's return values.
+ */
+struct ReturnInfo
+{
+	ReturnInfo(langutil::EVMVersion const& _evmVersion, FunctionType const& _functionType);
+
+	/// Vector of TypePointer, for each return variable. Dynamic types are already replaced if required.
+	TypePointers returnTypes = {};
+
+	/// Boolean, indicating whether or not return size is only known at runtime.
+	bool dynamicReturnSize = false;
+
+	/// Contains the at compile time estimated return size.
+	unsigned estimatedReturnSize = 0;
+};
+
+}

libsolidity/codegen/YulUtilFunctions.cpp

@@ -2252,3 +2252,84 @@ string YulUtilFunctions::revertReasonIfDebug(string const& _message)
 {
 	return revertReasonIfDebug(m_revertStrings, _message);
 }
+
+string YulUtilFunctions::tryDecodeErrorMessageFunction()
+{
+	string const functionName = "try_decode_error_message";
+
+	return m_functionCollector.createFunction(functionName, [&]() {
+		return util::Whiskers(R"(
+			function <functionName>() -> ret {
+				if lt(returndatasize(), 0x44) { leave }
+
+				returndatacopy(0, 0, 4)
+				let sig := <shr224>(mload(0))
+				if iszero(eq(sig, 0x<ErrorSignature>)) { leave }
+
+				let data := mload(<freeMemoryPointer>)
+				returndatacopy(data, 4, sub(returndatasize(), 4))
+
+				let offset := mload(data)
+				if or(
+					gt(offset, 0xffffffffffffffff),
+					gt(add(offset, 0x24), returndatasize())
+				) {
+					leave
+				}
+
+				let msg := add(data, offset)
+				let length := mload(msg)
+				if gt(length, 0xffffffffffffffff) { leave }
+
+				let end := add(add(msg, 0x20), length)
+				if gt(end, add(data, returndatasize())) { leave }
+
+				mstore(<freeMemoryPointer>, add(add(msg, 0x20), <roundUp>(length)))
+				ret := msg
+			}
+		)")
+		("functionName", functionName)
+		("shr224", shiftRightFunction(224))
+		("ErrorSignature", FixedHash<4>(util::keccak256("Error(string)")).hex())
+		("freeMemoryPointer", to_string(CompilerUtils::freeMemoryPointer))
+		("roundUp", roundUpFunction())
+		.render();
+	});
+}
+
+string YulUtilFunctions::extractReturndataFunction()
+{
+	string const functionName = "extract_returndata";
+
+	return m_functionCollector.createFunction(functionName, [&]() {
+		return util::Whiskers(R"(
+			function <functionName>() -> data {
+				<?supportsReturndata>
+					switch returndatasize()
+					case 0 {
+						data := <emptyArray>()
+					}
+					default {
+						// allocate some memory into data of size returndatasize() + PADDING
+						data := <allocate>(<roundUp>(add(returndatasize(), 0x20)))
+
+						// store array length into the front
+						mstore(data, returndatasize())
+
+						// append to data
+						returndatacopy(add(data, 0x20), 0, returndatasize())
+					}
+				<!supportsReturndata>
+					data := <emptyArray>()
+				</supportsReturndata>
+			}
+		)")
+		("functionName", functionName)
+		("supportsReturndata", m_evmVersion.supportsReturndata())
+		("allocate", allocationFunction())
+		("roundUp", roundUpFunction())
+		("emptyArray", zeroValueFunction(*TypeProvider::bytesMemory()))
+		.render();
+	});
+}
+

libsolidity/codegen/YulUtilFunctions.h

@@ -22,6 +22,7 @@
 
 #include <liblangutil/EVMVersion.h>
 
+#include <libsolidity/ast/Types.h>
 #include <libsolidity/codegen/MultiUseYulFunctionCollector.h>
 
 #include <libsolidity/interface/DebugSettings.h>
@@ -322,6 +323,20 @@ public:
 	static std::string revertReasonIfDebug(RevertStrings revertStrings, std::string const& _message = "");
 
 	std::string revertReasonIfDebug(std::string const& _message = "");
+
+	/// Returns the name of a function that decodes an error message.
+	/// signature: () -> arrayPtr
+	///
+	/// Returns a newly allocated `bytes memory` array containing the decoded error message
+	/// or 0 on failure.
+	std::string tryDecodeErrorMessageFunction();
+
+
+	/// Returns a function name that returns a newly allocated `bytes` array that contains the return data.
+	///
+	/// If returndatacopy() is not supported by the underlying target, a empty array will be returned instead.
+	std::string extractReturndataFunction();
+
 private:
 	/// Special case of conversionFunction - handles everything that does not
 	/// use exactly one variable to hold the value.

libsolidity/codegen/ir/IRGenerationContext.cpp

@@ -87,6 +87,17 @@ string IRGenerationContext::newYulVariable()
 	return "_" + to_string(++m_varCounter);
 }
 
+string IRGenerationContext::trySuccessConditionVariable(Expression const& _expression) const
+{
+	// NB: The TypeChecker already ensured that the Expression is of type FunctionCall.
+	solAssert(
+		static_cast<FunctionCallAnnotation const&>(_expression.annotation()).tryCall,
+		"Parameter must be a FunctionCall with tryCall-annotation set."
+	);
+
+	return "trySuccessCondition_" + to_string(_expression.id());
+}
+
 string IRGenerationContext::internalDispatch(size_t _in, size_t _out)
 {
 	string funName = "dispatch_internal_in_" + to_string(_in) + "_out_" + to_string(_out);
@@ -141,3 +152,4 @@ std::string IRGenerationContext::revertReasonIfDebug(std::string const& _message
 {
 	return YulUtilFunctions::revertReasonIfDebug(m_revertStrings, _message);
 }
+

libsolidity/codegen/ir/IRGenerationContext.h

@@ -99,6 +99,10 @@ public:
 
 	RevertStrings revertStrings() const { return m_revertStrings; }
 
+	/// @returns the variable name that can be used to inspect the success or failure of an external
+	/// function call that was invoked as part of the try statement.
+	std::string trySuccessConditionVariable(Expression const& _expression) const;
+
 private:
 	langutil::EVMVersion m_evmVersion;
 	RevertStrings m_revertStrings;

libsolidity/codegen/ir/IRGeneratorForStatements.cpp

@@ -27,6 +27,7 @@
 #include <libsolidity/codegen/YulUtilFunctions.h>
 #include <libsolidity/codegen/ABIFunctions.h>
 #include <libsolidity/codegen/CompilerUtils.h>
+#include <libsolidity/codegen/ReturnInfo.h>
 #include <libsolidity/ast/TypeProvider.h>
 
 #include <libevmasm/GasMeter.h>
@@ -41,6 +42,7 @@
 #include <libsolutil/Keccak256.h>
 #include <libsolutil/Visitor.h>
 
+#include <boost/range/adaptor/reversed.hpp>
 #include <boost/range/adaptor/transformed.hpp>
 
 using namespace std;
@@ -1260,39 +1262,15 @@ void IRGeneratorForStatements::appendExternalFunctionCall(
 		_arguments.size() == funType.parameterTypes().size(), ""
 	);
 	solUnimplementedAssert(!funType.bound(), "");
-	FunctionType::Kind funKind = funType.kind();
+	FunctionType::Kind const funKind = funType.kind();
 
 	solAssert(funKind != FunctionType::Kind::BareStaticCall || m_context.evmVersion().hasStaticCall(), "");
 	solAssert(funKind != FunctionType::Kind::BareCallCode, "Callcode has been removed.");
 
-	bool returnSuccessConditionAndReturndata = funKind == FunctionType::Kind::BareCall || funKind == FunctionType::Kind::BareDelegateCall || funKind == FunctionType::Kind::BareStaticCall;
-	bool isDelegateCall = funKind == FunctionType::Kind::BareDelegateCall || funKind == FunctionType::Kind::DelegateCall;
-	bool useStaticCall = funKind == FunctionType::Kind::BareStaticCall || (funType.stateMutability() <= StateMutability::View && m_context.evmVersion().hasStaticCall());
+	bool const isDelegateCall = funKind == FunctionType::Kind::BareDelegateCall || funKind == FunctionType::Kind::DelegateCall;
+	bool const useStaticCall = funKind == FunctionType::Kind::BareStaticCall || (funType.stateMutability() <= StateMutability::View && m_context.evmVersion().hasStaticCall());
 
-	bool haveReturndatacopy = m_context.evmVersion().supportsReturndata();
-	unsigned estimatedReturnSize = 0;
-	bool dynamicReturnSize = false;
-	TypePointers returnTypes;
-	if (!returnSuccessConditionAndReturndata)
-	{
-		if (haveReturndatacopy)
-			returnTypes = funType.returnParameterTypes();
-		else
-			returnTypes = funType.returnParameterTypesWithoutDynamicTypes();
-
-		for (auto const& retType: returnTypes)
-			if (retType->isDynamicallyEncoded())
-			{
-				solAssert(haveReturndatacopy, "");
-				dynamicReturnSize = true;
-				estimatedReturnSize = 0;
-				break;
-			}
-			else if (retType->decodingType())
-				estimatedReturnSize += retType->decodingType()->calldataEncodedSize();
-			else
-				estimatedReturnSize += retType->calldataEncodedSize();
-	}
+	ReturnInfo const returnInfo{m_context.evmVersion(), funType};
 
 	TypePointers argumentTypes;
 	vector<string> argumentStrings;
@@ -1311,8 +1289,8 @@ void IRGeneratorForStatements::appendExternalFunctionCall(
 		// (which we would have to subtract from the gas left)
 		// We could also just use MLOAD; POP right before the gas calculation, but the optimizer
 		// would remove that, so we use MSTORE here.
-		if (!funType.gasSet() && estimatedReturnSize > 0)
-			m_code << "mstore(add(" << freeMemory() << ", " << to_string(estimatedReturnSize) << "), 0)\n";
+		if (!funType.gasSet() && returnInfo.estimatedReturnSize > 0)
+			m_code << "mstore(add(" << freeMemory() << ", " << to_string(returnInfo.estimatedReturnSize) << "), 0)\n";
 	}
 
 	ABIFunctions abi(m_context.evmVersion(), m_context.revertStrings(), m_context.functionCollector());
@@ -1323,30 +1301,61 @@ void IRGeneratorForStatements::appendExternalFunctionCall(
 			if iszero(extcodesize(<address>)) { revert(0, 0) }
 		</checkExistence>
 
+		// storage for arguments and returned data
 		let <pos> := <freeMemory>
-
 		mstore(<pos>, <shl28>(<funId>))
 		let <end> := <encodeArgs>(add(<pos>, 4) <argumentString>)
 
-		let <result> := <call>(<gas>, <address>, <?hasValue> <value>, </hasValue> <pos>, sub(<end>, <pos>), <pos>, <reservedReturnSize>)
-		if iszero(<result>) { <forwardingRevert>() }
+		let <success> := <call>(<gas>, <address>, <?hasValue> <value>, </hasValue> <pos>, sub(<end>, <pos>), <pos>, <reservedReturnSize>)
+		<?noTryCall>
+			if iszero(<success>) { <forwardingRevert>() }
+		</noTryCall>
+		<?hasRetVars> let <retVars> </hasRetVars>
+		if <success> {
+			<?dynamicReturnSize>
+				// copy dynamic return data out
+				returndatacopy(<pos>, 0, returndatasize())
+			</dynamicReturnSize>
 
-		<?dynamicReturnSize>
-			returndatacopy(<pos>, 0, returndatasize())
-		</dynamicReturnSize>
+			// update freeMemoryPointer according to dynamic return size
+			mstore(<freeMemoryPointer>, add(<pos>, <roundUp>(<returnSize>)))
 
-		mstore(<freeMemoryPointer>, add(<pos>, and(add(<returnSize>, 0x1f), not(0x1f))))
-		<?returns> let <retVars> := </returns> <abiDecode>(<pos>, add(<pos>, <returnSize>))
+			// decode return parameters from external try-call into retVars
+			<?hasRetVars> <retVars> := </hasRetVars> <abiDecode>(<pos>, add(<pos>, <returnSize>))
+		}
 	)");
 	templ("pos", m_context.newYulVariable());
 	templ("end", m_context.newYulVariable());
-	templ("result", m_context.newYulVariable());
+	if (_functionCall.annotation().tryCall)
+		templ("success", m_context.trySuccessConditionVariable(_functionCall));
+	else
+		templ("success", m_context.newYulVariable());
 	templ("freeMemory", freeMemory());
-	templ("freeMemoryPointer", to_string(CompilerUtils::freeMemoryPointer));
 	templ("shl28", m_utils.shiftLeftFunction(8 * (32 - 4)));
 	templ("funId", IRVariable(_functionCall.expression()).part("functionIdentifier").name());
 	templ("address", IRVariable(_functionCall.expression()).part("address").name());
 
+	// Always use the actual return length, and not our calculated expected length, if returndatacopy is supported.
+	// This ensures it can catch badly formatted input from external calls.
+	if (m_context.evmVersion().supportsReturndata())
+		templ("returnSize", "returndatasize()");
+	else
+		templ("returnSize", to_string(returnInfo.estimatedReturnSize));
+
+	templ("reservedReturnSize", returnInfo.dynamicReturnSize ? "0" : to_string(returnInfo.estimatedReturnSize));
+
+	string const retVars = IRVariable(_functionCall).commaSeparatedList();
+	templ("retVars", retVars);
+	templ("hasRetVars", !retVars.empty());
+	solAssert(retVars.empty() == returnInfo.returnTypes.empty(), "");
+
+	templ("roundUp", m_utils.roundUpFunction());
+	templ("abiDecode", abi.tupleDecoder(returnInfo.returnTypes, true));
+	templ("dynamicReturnSize", returnInfo.dynamicReturnSize);
+	templ("freeMemoryPointer", to_string(CompilerUtils::freeMemoryPointer));
+
+	templ("noTryCall", !_functionCall.annotation().tryCall);
+
 	// If the function takes arbitrary parameters or is a bare call, copy dynamic length data in place.
 	// Move arguments to memory, will not update the free memory pointer (but will update the memory
 	// pointer on the stack).
@@ -1401,24 +1410,9 @@ void IRGeneratorForStatements::appendExternalFunctionCall(
 
 	templ("forwardingRevert", m_utils.forwardingRevertFunction());
 
-	solUnimplementedAssert(!returnSuccessConditionAndReturndata, "");
 	solUnimplementedAssert(funKind != FunctionType::Kind::RIPEMD160, "");
 	solUnimplementedAssert(funKind != FunctionType::Kind::ECRecover, "");
 
-	templ("dynamicReturnSize", dynamicReturnSize);
-	// Always use the actual return length, and not our calculated expected length, if returndatacopy is supported.
-	// This ensures it can catch badly formatted input from external calls.
-	if (haveReturndatacopy)
-		templ("returnSize", "returndatasize()");
-	else
-		templ("returnSize", to_string(estimatedReturnSize));
-
-	templ("reservedReturnSize", dynamicReturnSize ? "0" : to_string(estimatedReturnSize));
-
-	templ("abiDecode", abi.tupleDecoder(returnTypes, true));
-	templ("returns", !returnTypes.empty());
-	templ("retVars", IRVariable(_functionCall).commaSeparatedList());
-
 	m_code << templ.render();
 }
 
@@ -1749,3 +1743,119 @@ Type const& IRGeneratorForStatements::type(Expression const& _expression)
 	solAssert(_expression.annotation().type, "Type of expression not set.");
 	return *_expression.annotation().type;
 }
+
+bool IRGeneratorForStatements::visit(TryStatement const& _tryStatement)
+{
+	Expression const& externalCall = _tryStatement.externalCall();
+	externalCall.accept(*this);
+
+	m_code << "switch iszero(" << m_context.trySuccessConditionVariable(externalCall) << ")\n";
+
+	m_code << "case 0 { // success case\n";
+	TryCatchClause const& successClause = *_tryStatement.clauses().front();
+	if (successClause.parameters())
+	{
+		size_t i = 0;
+		for (ASTPointer<VariableDeclaration> const& varDecl: successClause.parameters()->parameters())
+		{
+			solAssert(varDecl, "");
+			define(m_context.addLocalVariable(*varDecl),
+				successClause.parameters()->parameters().size() == 1 ?
+				IRVariable(externalCall) :
+				IRVariable(externalCall).tupleComponent(i++)
+			);
+		}
+	}
+
+	successClause.block().accept(*this);
+	m_code << "}\n";
+
+	m_code << "default { // failure case\n";
+	handleCatch(_tryStatement);
+	m_code << "}\n";
+
+	return false;
+}
+
+void IRGeneratorForStatements::handleCatch(TryStatement const& _tryStatement)
+{
+	if (_tryStatement.structuredClause())
+		handleCatchStructuredAndFallback(*_tryStatement.structuredClause(), _tryStatement.fallbackClause());
+	else if (_tryStatement.fallbackClause())
+		handleCatchFallback(*_tryStatement.fallbackClause());
+	else
+		rethrow();
+}
+
+void IRGeneratorForStatements::handleCatchStructuredAndFallback(
+	TryCatchClause const& _structured,
+	TryCatchClause const* _fallback
+)
+{
+	solAssert(
+		_structured.parameters() &&
+		_structured.parameters()->parameters().size() == 1 &&
+		_structured.parameters()->parameters().front() &&
+		*_structured.parameters()->parameters().front()->annotation().type == *TypeProvider::stringMemory(),
+		""
+	);
+	solAssert(m_context.evmVersion().supportsReturndata(), "");
+
+	// Try to decode the error message.
+	// If this fails, leaves 0 on the stack, otherwise the pointer to the data string.
+	string const dataVariable = m_context.newYulVariable();
+
+	m_code << "let " << dataVariable << " := " << m_utils.tryDecodeErrorMessageFunction() << "()\n";
+	m_code << "switch iszero(" << dataVariable << ") \n";
+	m_code << "case 0 { // decoding success\n";
+	if (_structured.parameters())
+	{
+		solAssert(_structured.parameters()->parameters().size() == 1, "");
+		IRVariable const& var = m_context.addLocalVariable(*_structured.parameters()->parameters().front());
+		define(var) << dataVariable << "\n";
+	}
+	_structured.accept(*this);
+	m_code << "}\n";
+	m_code << "default { // decoding failure\n";
+	if (_fallback)
+		handleCatchFallback(*_fallback);
+	else
+		rethrow();
+	m_code << "}\n";
+}
+
+void IRGeneratorForStatements::handleCatchFallback(TryCatchClause const& _fallback)
+{
+	if (_fallback.parameters())
+	{
+		solAssert(m_context.evmVersion().supportsReturndata(), "");
+		solAssert(
+			_fallback.parameters()->parameters().size() == 1 &&
+			_fallback.parameters()->parameters().front() &&
+			*_fallback.parameters()->parameters().front()->annotation().type == *TypeProvider::bytesMemory(),
+			""
+		);
+
+		VariableDeclaration const& paramDecl = *_fallback.parameters()->parameters().front();
+		define(m_context.addLocalVariable(paramDecl)) << m_utils.extractReturndataFunction() << "()\n";
+	}
+	_fallback.accept(*this);
+}
+
+void IRGeneratorForStatements::rethrow()
+{
+	if (m_context.evmVersion().supportsReturndata())
+		m_code << R"(
+			returndatacopy(0, 0, returndatasize())
+			revert(0, returndatasize())
+		)"s;
+	else
+		m_code << "revert(0, 0) // rethrow\n"s;
+}
+
+bool IRGeneratorForStatements::visit(TryCatchClause const& _clause)
+{
+	_clause.block().accept(*this);
+	return false;
+}
+

libsolidity/codegen/ir/IRGeneratorForStatements.h

@@ -24,6 +24,8 @@
 #include <libsolidity/codegen/ir/IRLValue.h>
 #include <libsolidity/codegen/ir/IRVariable.h>
 
+#include <functional>
+
 namespace solidity::frontend
 {
 
@@ -70,7 +72,21 @@ public:
 	void endVisit(Identifier const& _identifier) override;
 	bool visit(Literal const& _literal) override;
 
+	bool visit(TryStatement const& _tryStatement) override;
+	bool visit(TryCatchClause const& _tryCatchClause) override;
+
 private:
+	/// Handles all catch cases of a try statement, except the success-case.
+	void handleCatch(TryStatement const& _tryStatement);
+	void handleCatchStructuredAndFallback(
+		TryCatchClause const& _structured,
+		TryCatchClause const* _fallback
+	);
+	void handleCatchFallback(TryCatchClause const& _fallback);
+
+	/// Generates code to rethrow an exception.
+	void rethrow();
+
 	/// Appends code to call an external function with the given arguments.
 	/// All involved expressions have already been visited.
 	void appendExternalFunctionCall(

test/libsolidity/semanticTests/tryCatch/lowLevel.sol

@@ -12,6 +12,7 @@ contract C {
     }
 }
 // ====
+// compileViaYul: also
 // EVMVersion: >=byzantium
 // ----
 // f(bool): true -> 1, 2, 96, 0

test/libsolidity/semanticTests/tryCatch/nested.sol

@@ -26,6 +26,7 @@ contract C {
 }
 // ====
 // EVMVersion: >=byzantium
+// compileViaYul: also
 // ----
 // f(bool,bool): true, true -> 1, 2, 96, 7, "success"
 // f(bool,bool): true, false -> 12, 0, 96, 7, "failure"

test/libsolidity/semanticTests/tryCatch/return_function.sol

@@ -13,5 +13,7 @@ contract C {
     }
     function fun() public pure {}
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 0x1, 0xfdd67305928fcac8d213d1e47bfa6165cd0b87b946644cd0000000000000000, 9

test/libsolidity/semanticTests/tryCatch/simple.sol

@@ -1,10 +1,10 @@
 contract C {
-    function g(bool b) public pure returns (uint, uint) {
+    function g(bool b) public pure returns (uint x, uint y) {
         require(b);
         return (1, 2);
     }
-    function f(bool b) public returns (uint x, uint y) {
-        try this.g(b) returns (uint a, uint b) {
+    function f(bool flag) public view returns (uint x, uint y) {
+        try this.g(flag) returns (uint a, uint b) {
             (x, y) = (a, b);
         } catch {
             (x, y) = (9, 10);
@@ -13,6 +13,7 @@ contract C {
 }
 // ====
 // EVMVersion: >=byzantium
+// compileViaYul: also
 // ----
 // f(bool): true -> 1, 2
 // f(bool): false -> 9, 10

test/libsolidity/semanticTests/tryCatch/simple_notuple.sol

@@ -0,0 +1,19 @@
+contract C {
+    function g(bool b) public pure returns (uint x) {
+        require(b);
+        return 13;
+    }
+    function f(bool flag) public view returns (uint x) {
+        try this.g(flag) returns (uint a) {
+            x = a;
+        } catch {
+            x = 9;
+        }
+    }
+}
+// ====
+// EVMVersion: >=byzantium
+// compileViaYul: also
+// ----
+// f(bool): true -> 13
+// f(bool): false -> 9

test/libsolidity/semanticTests/tryCatch/structured.sol

@@ -14,6 +14,7 @@ contract C {
 }
 // ====
 // EVMVersion: >=byzantium
+// compileViaYul: also
 // ----
 // f(bool): true -> 1, 2, 0x60, 7, "success"
 // f(bool): false -> 0, 0, 0x60, 7, "message"

test/libsolidity/semanticTests/tryCatch/structuredAndLowLevel.sol

@@ -18,6 +18,7 @@ contract C {
 }
 // ====
 // EVMVersion: >=byzantium
+// compileViaYul: also
 // ----
 // f(bool): true -> 1, 2, 96, 7, "success"
 // f(bool): false -> 99, 0, 96, 82, "message longer than 32 bytes 32 ", "bytes 32 bytes 32 bytes 32 bytes", " 32 bytes 32 bytes"

test/libsolidity/semanticTests/tryCatch/super_trivial.sol

@@ -0,0 +1,18 @@
+contract C {
+    function g(bool x) external pure {
+        require(x);
+    }
+    function f(bool x) public returns (uint) {
+        try this.g(x) {
+            return 1;
+        } catch {
+            return 2;
+        }
+    }
+}
+// ====
+// EVMVersion: >=byzantium
+// compileViaYul: also
+// ----
+// f(bool): true -> 1
+// f(bool): false -> 2