Merge pull request #16041 from ethereum/ssacfg_treat_literals_as_variables

Add option to treat literal assignments as operations in SSACFGs

Author: clonker

libyul/YulControlFlowGraphExporter.cpp

@@ -177,12 +177,20 @@ Json YulControlFlowGraphExporter::toJson(SSACFG const& _cfg, SSACFG::BlockId _bl
 Json YulControlFlowGraphExporter::toJson(Json& _ret, SSACFG const& _cfg, SSACFG::Operation const& _operation)
 {
 	Json opJson = Json::object();
-	std::visit(util::GenericVisitor{
-		[&](SSACFG::Call const& _call) {
+	std::visit(GenericVisitor{
+		[&](SSACFG::Call const& _call)
+		{
 			_ret["type"] = "FunctionCall";
 			opJson["op"] = _call.function.get().name.str();
 		},
-		[&](SSACFG::BuiltinCall const& _call) {
+		[&](SSACFG::LiteralAssignment const&)
+		{
+			yulAssert(_operation.inputs.size() == 1);
+			yulAssert(_cfg.isLiteralValue(_operation.inputs.back()));
+			_ret["type"] = "LiteralAssignment";
+		},
+		[&](SSACFG::BuiltinCall const& _call)
+		{
 			_ret["type"] = "BuiltinCall";
 			Json builtinArgsJson = Json::array();
 			auto const& builtin = _call.builtin.get();

libyul/YulStack.cpp

@@ -394,11 +394,15 @@ Json YulStack::cfgJson() const
 	yulAssert(m_parserResult->analysisInfo, "");
 	// FIXME: we should not regenerate the cfg, but for now this is sufficient for testing purposes
 	auto exportCFGFromObject = [&](Object const& _object) -> Json {
+		// with this set to `true`, assignments of the type `let x := 42` are preserved and added as assignment
+		// operations to the control flow graphs
+		bool constexpr keepLiteralAssignments = true;
 		// NOTE: The block Ids are reset for each object
 		std::unique_ptr<ControlFlow> controlFlow = SSAControlFlowGraphBuilder::build(
-			*_object.analysisInfo.get(),
+			*_object.analysisInfo,
 			languageToDialect(m_language, m_evmVersion, m_eofVersion),
-			_object.code()->root()
+			_object.code()->root(),
+			keepLiteralAssignments
 		);
 		std::unique_ptr<ControlFlowLiveness> liveness = std::make_unique<ControlFlowLiveness>(*controlFlow);
 		YulControlFlowGraphExporter exporter(*controlFlow, liveness.get());

libyul/backends/evm/SSAControlFlowGraph.cpp

@@ -168,17 +168,28 @@ class SSACFGPrinter
 					[&](SSACFG::BuiltinCall const& _call) {
 						return _call.builtin.get().name;
 					},
+					[&](SSACFG::LiteralAssignment const&)
+					{
+						yulAssert(operation.inputs.size() == 1);
+						return varToString(m_cfg, operation.inputs.back());
+					}
 				}, operation.kind);
 				if (!operation.outputs.empty())
 					m_result << fmt::format(
 						"{} := ",
 						fmt::join(operation.outputs | ranges::views::transform(valueToString), ", ")
 					);
-				m_result << fmt::format(
-					"{}({})\\l\\\n",
-					escape(label),
-					fmt::join(operation.inputs | ranges::views::transform(valueToString), ", ")
-				);
+				if (std::holds_alternative<SSACFG::LiteralAssignment>(operation.kind))
+					m_result << fmt::format(
+						"{}\\l\\\n",
+						escape(label)
+					);
+				else
+					m_result << fmt::format(
+						"{}({})\\l\\\n",
+						escape(label),
+						fmt::join(operation.inputs | ranges::views::transform(valueToString), ", ")
+					);
 			}
 			m_result << "\"];\n";
 			std::visit(GenericVisitor{

libyul/backends/evm/SSAControlFlowGraph.h

@@ -78,10 +78,14 @@ class SSACFG
 		std::reference_wrapper<FunctionCall const> call;
 		bool canContinue;
 	};
+	struct LiteralAssignment
+	{
+		langutil::DebugData::ConstPtr debugData;
+	};
 
 	struct Operation {
 		std::vector<ValueId> outputs{};
-		std::variant<BuiltinCall, Call> kind;
+		std::variant<BuiltinCall, Call, LiteralAssignment> kind;
 		std::vector<ValueId> inputs{};
 	};
 	struct BasicBlock
@@ -199,7 +203,7 @@ class SSACFG
 	}
 	ValueId newLiteral(langutil::DebugData::ConstPtr _debugData, u256 _value)
 	{
-		auto [it, inserted] = m_literals.emplace(_value, SSACFG::ValueId{m_valueInfos.size()});
+		auto [it, inserted] = m_literals.emplace(_value, ValueId{m_valueInfos.size()});
 		if (inserted)
 			m_valueInfos.emplace_back(LiteralValue{std::move(_debugData), _value});
 		else

libyul/backends/evm/SSAControlFlowGraphBuilder.cpp

@@ -20,16 +20,18 @@
  */
 
 #include <libyul/backends/evm/SSAControlFlowGraphBuilder.h>
-#include <libyul/AST.h>
-#include <libyul/Exceptions.h>
+
 #include <libyul/backends/evm/ControlFlow.h>
+#include <libyul/AST.h>
 #include <libyul/ControlFlowSideEffectsCollector.h>
+#include <libyul/Exceptions.h>
 #include <libyul/Utilities.h>
 
 #include <libsolutil/Algorithms.h>
 #include <libsolutil/StringUtils.h>
 #include <libsolutil/Visitor.h>
 
+#include <range/v3/algorithm/replace.hpp>
 #include <range/v3/range/conversion.hpp>
 #include <range/v3/view/drop_last.hpp>
 #include <range/v3/view/enumerate.hpp>
@@ -49,26 +51,29 @@ SSAControlFlowGraphBuilder::SSAControlFlowGraphBuilder(
 	SSACFG& _graph,
 	AsmAnalysisInfo const& _analysisInfo,
 	ControlFlowSideEffectsCollector const& _sideEffects,
-	Dialect const& _dialect
+	Dialect const& _dialect,
+	bool _keepLiteralAssignments
 ):
 	m_controlFlow(_controlFlow),
 	m_graph(_graph),
 	m_info(_analysisInfo),
 	m_sideEffects(_sideEffects),
-	m_dialect(_dialect)
+	m_dialect(_dialect),
+	m_keepLiteralAssignments(_keepLiteralAssignments)
 {
 }
 
 std::unique_ptr<ControlFlow> SSAControlFlowGraphBuilder::build(
 	AsmAnalysisInfo const& _analysisInfo,
 	Dialect const& _dialect,
-	Block const& _block
+	Block const& _block,
+	bool _keepLiteralAssignments
 )
 {
 	ControlFlowSideEffectsCollector sideEffects(_dialect, _block);
 
 	auto controlFlow = std::make_unique<ControlFlow>();
-	SSAControlFlowGraphBuilder builder(*controlFlow, *controlFlow->mainGraph, _analysisInfo, sideEffects, _dialect);
+	SSAControlFlowGraphBuilder builder(*controlFlow, *controlFlow->mainGraph, _analysisInfo, sideEffects, _dialect, _keepLiteralAssignments);
 	builder.m_currentBlock = controlFlow->mainGraph->makeBlock(debugDataOf(_block));
 	builder.sealBlock(builder.m_currentBlock);
 	builder(_block);
@@ -147,8 +152,8 @@ SSACFG::ValueId SSAControlFlowGraphBuilder::tryRemoveTrivialPhi(SSACFG::ValueId
 			[](SSACFG::BasicBlock::Terminated&) {}
 		}, block.exit);
 	}
-	for (auto& [_, currentVariableDefs]: m_currentDef)
-		std::replace(currentVariableDefs.begin(), currentVariableDefs.end(), _phi, same);
+	for (auto& currentVariableDefs: m_currentDef | ranges::views::values)
+		ranges::replace(currentVariableDefs, _phi, same);
 
 	for (auto phiUse: phiUses)
 		tryRemoveTrivialPhi(phiUse);
@@ -178,11 +183,6 @@ void SSAControlFlowGraphBuilder::cleanUnreachable()
 			}, block.exit);
 	});
 
-	auto isUnreachableValue = [&](SSACFG::ValueId const& _value) -> bool {
-		auto* valueInfo = std::get_if<SSACFG::UnreachableValue>(&m_graph.valueInfo(_value));
-		return (valueInfo) ? true : false;
-	};
-
 	// Remove all entries from unreachable nodes from the graph.
 	for (SSACFG::BlockId blockId: reachabilityCheck.visited)
 	{
@@ -197,7 +197,7 @@ void SSAControlFlowGraphBuilder::cleanUnreachable()
 		for (auto phi: block.phis)
 			if (auto* phiInfo = std::get_if<SSACFG::PhiValue>(&m_graph.valueInfo(phi)))
 				std::erase_if(phiInfo->arguments, [&](SSACFG::ValueId _arg) {
-					if (isUnreachableValue(_arg))
+					if (std::holds_alternative<SSACFG::UnreachableValue>(m_graph.valueInfo(_arg)))
 					{
 						maybeTrivialPhi.insert(phi);
 						return true;
@@ -240,7 +240,7 @@ void SSAControlFlowGraphBuilder::buildFunctionGraph(
 	cfg.arguments = arguments;
 	cfg.returns = returns;
 
-	SSAControlFlowGraphBuilder builder(m_controlFlow, cfg, m_info, m_sideEffects, m_dialect);
+	SSAControlFlowGraphBuilder builder(m_controlFlow, cfg, m_info, m_sideEffects, m_dialect, m_keepLiteralAssignments);
 	builder.m_currentBlock = cfg.entry;
 	builder.m_functionDefinitions = m_functionDefinitions;
 	for (auto&& [var, varId]: cfg.arguments)
@@ -273,6 +273,11 @@ void SSAControlFlowGraphBuilder::operator()(Assignment const& _assignment)
 
 void SSAControlFlowGraphBuilder::operator()(VariableDeclaration const& _variableDeclaration)
 {
+	// if we have no value (like in `let a` without right-hand side), we can just skip this. the variable(s) will be
+	// added when first needed
+	if (!_variableDeclaration.value)
+		return;
+
 	assign(
 		_variableDeclaration.variables | ranges::views::transform([&](auto& _var) { return std::ref(lookupVariable(_var.name)); }) | ranges::to<std::vector>,
 		_variableDeclaration.value.get()
@@ -533,15 +538,27 @@ void SSAControlFlowGraphBuilder::assign(std::vector<std::reference_wrapper<Scope
 	auto rhs = [&]() -> std::vector<SSACFG::ValueId> {
 		if (auto const* functionCall = std::get_if<FunctionCall>(_expression))
 			return visitFunctionCall(*functionCall);
-		else if (_expression)
+		if (_expression)
 			return {std::visit(*this, *_expression)};
-		else
-			return {_variables.size(), zero()};
+		return {_variables.size(), zero()};
 	}();
 	yulAssert(rhs.size() == _variables.size());
 
 	for (auto const& [var, value]: ranges::zip_view(_variables, rhs))
-		writeVariable(var, m_currentBlock, value);
+	{
+		if (m_keepLiteralAssignments && m_graph.isLiteralValue(value))
+		{
+			SSACFG::Operation assignment{
+				.outputs = {m_graph.newVariable(m_currentBlock)},
+				.kind = SSACFG::LiteralAssignment{},
+				.inputs = {value}
+			};
+			currentBlock().operations.emplace_back(assignment);
+			writeVariable(var, m_currentBlock, assignment.outputs.back());
+		}
+		else
+			writeVariable(var, m_currentBlock, value);
+	}
 
 }
 
@@ -610,7 +627,7 @@ SSACFG::ValueId SSAControlFlowGraphBuilder::readVariableRecursive(Scope::Variabl
 		// incomplete block
 		val = m_graph.newPhi(_block);
 		block.phis.insert(val);
-		info.incompletePhis.emplace_back(val, std::ref(_variable));
+		info.incompletePhis.emplace_back(val, _variable);
 	}
 	else if (block.entries.size() == 1)
 		// one predecessor: no phi needed
@@ -633,7 +650,7 @@ SSACFG::ValueId SSAControlFlowGraphBuilder::addPhiOperands(Scope::Variable const
 {
 	yulAssert(std::holds_alternative<SSACFG::PhiValue>(m_graph.valueInfo(_phi)));
 	auto& phi = std::get<SSACFG::PhiValue>(m_graph.valueInfo(_phi));
-	for (auto pred: m_graph.block(phi.block).entries)
+	for (auto const& pred: m_graph.block(phi.block).entries)
 		phi.arguments.emplace_back(readVariable(_variable, pred));
 	// we call tryRemoveTrivialPhi explicitly to avoid removing trivial phis in unsealed blocks
 	return _phi;
@@ -660,14 +677,14 @@ Scope::Variable const& SSAControlFlowGraphBuilder::lookupVariable(YulName _name)
 	yulAssert(m_scope, "");
 	Scope::Variable const* var = nullptr;
 	if (m_scope->lookup(_name, util::GenericVisitor{
-		[&](Scope::Variable& _var) { var = &_var; },
-		[](Scope::Function&)
+		[&](Scope::Variable const& _var) { var = &_var; },
+		[](Scope::Function const&)
 		{
 			yulAssert(false, "Function not removed during desugaring.");
 		}
 	}))
 	{
-		yulAssert(var, "");
+		yulAssert(var);
 		return *var;
 	};
 	yulAssert(false, "External identifier access unimplemented.");

libyul/backends/evm/SSAControlFlowGraphBuilder.h

@@ -44,15 +44,17 @@ class SSAControlFlowGraphBuilder
 		SSACFG& _graph,
 		AsmAnalysisInfo const& _analysisInfo,
 		ControlFlowSideEffectsCollector const& _sideEffects,
-		Dialect const& _dialect
+		Dialect const& _dialect,
+		bool _keepLiteralAssignments
 	);
 public:
 	SSAControlFlowGraphBuilder(SSAControlFlowGraphBuilder const&) = delete;
 	SSAControlFlowGraphBuilder& operator=(SSAControlFlowGraphBuilder const&) = delete;
 	static std::unique_ptr<ControlFlow> build(
 		AsmAnalysisInfo const& _analysisInfo,
 		Dialect const& _dialect,
-		Block const& _block
+		Block const& _block,
+		bool _keepLiteralAssignments
 	);
 
 	void operator()(ExpressionStatement const& _statement);
@@ -92,6 +94,7 @@ class SSAControlFlowGraphBuilder
 	AsmAnalysisInfo const& m_info;
 	ControlFlowSideEffectsCollector const& m_sideEffects;
 	Dialect const& m_dialect;
+	bool const m_keepLiteralAssignments;
 	std::vector<std::tuple<Scope::Function const*, FunctionDefinition const*>> m_functionDefinitions;
 	SSACFG::BlockId m_currentBlock;
 	SSACFG::BasicBlock& currentBlock() { return m_graph.block(m_currentBlock); }