Take user function side-effects into account for unused pruner.

libyul/optimiser/Semantics.cpp

@@ -35,8 +35,12 @@ using namespace dev;
 using namespace yul;
 
 
-SideEffectsCollector::SideEffectsCollector(Dialect const& _dialect, Expression const& _expression):
+SideEffectsCollector::SideEffectsCollector(
-	SideEffectsCollector(_dialect)
+		Dialect const& _dialect,
+		Expression const& _expression,
+		map<YulString, SideEffects> const* _functionSideEffects
+):
+	SideEffectsCollector(_dialect, _functionSideEffects)
 {
 	visit(_expression);
 }

libyul/optimiser/Semantics.h

@@ -41,7 +41,11 @@ public:
 		Dialect const& _dialect,
 		std::map<YulString, SideEffects> const* _functionSideEffects = nullptr
 	): m_dialect(_dialect), m_functionSideEffects(_functionSideEffects) {}
-	SideEffectsCollector(Dialect const& _dialect, Expression const& _expression);
+	SideEffectsCollector(
+		Dialect const& _dialect,
+		Expression const& _expression,
+		std::map<YulString, SideEffects> const* _functionSideEffects = nullptr
+	);
 	SideEffectsCollector(Dialect const& _dialect, Statement const& _statement);
 	SideEffectsCollector(Dialect const& _dialect, Block const& _ast);
 

libyul/optimiser/Suite.cpp

@@ -87,7 +87,7 @@ void OptimiserSuite::run(
 	DeadCodeEliminator{_dialect}(ast);
 	FunctionGrouper{}(ast);
 	EquivalentFunctionCombiner::run(ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 	BlockFlattener{}(ast);
 	ControlFlowSimplifier{_dialect}(ast);
 	StructuralSimplifier{_dialect}(ast);
@@ -127,20 +127,20 @@ void OptimiserSuite::run(
 			ControlFlowSimplifier{_dialect}(ast);
 			BlockFlattener{}(ast);
 			DeadCodeEliminator{_dialect}(ast);
-			UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+			UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 		}
 
 		{
 			// simplify again
 			CommonSubexpressionEliminator::run(_dialect, ast);
-			UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+			UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 		}
 
 		{
 			// reverse SSA
 			SSAReverser::run(ast);
 			CommonSubexpressionEliminator::run(_dialect, ast);
-			UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+			UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 
 			ExpressionJoiner::run(ast);
 			ExpressionJoiner::run(ast);
@@ -151,7 +151,7 @@ void OptimiserSuite::run(
 		{
 			// run functional expression inliner
 			ExpressionInliner(_dialect, ast).run();
-			UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+			UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 		}
 
 		{
@@ -185,7 +185,7 @@ void OptimiserSuite::run(
 			SSATransform::run(ast, dispenser);
 			RedundantAssignEliminator::run(_dialect, ast);
 			RedundantAssignEliminator::run(_dialect, ast);
-			UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+			UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 			CommonSubexpressionEliminator::run(_dialect, ast);
 		}
 	}
@@ -194,19 +194,19 @@ void OptimiserSuite::run(
 
 	ExpressionJoiner::run(ast);
 	Rematerialiser::run(_dialect, ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 	ExpressionJoiner::run(ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 	ExpressionJoiner::run(ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 
 	SSAReverser::run(ast);
 	CommonSubexpressionEliminator::run(_dialect, ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 
 	ExpressionJoiner::run(ast);
 	Rematerialiser::run(_dialect, ast);
-	UnusedPruner::runUntilStabilised(_dialect, ast, reservedIdentifiers);
+	UnusedPruner::runUntilStabilisedOnFullAST(_dialect, ast, reservedIdentifiers);
 
 	// This is a tuning parameter, but actually just prevents infinite loops.
 	size_t stackCompressorMaxIterations = 16;

libyul/optimiser/UnusedPruner.cpp

@@ -20,12 +20,14 @@
 
 #include <libyul/optimiser/UnusedPruner.h>
 
+#include <libyul/optimiser/CallGraphGenerator.h>
 #include <libyul/optimiser/NameCollector.h>
 #include <libyul/optimiser/Semantics.h>
 #include <libyul/optimiser/OptimizerUtilities.h>
 #include <libyul/Exceptions.h>
 #include <libyul/AsmData.h>
 #include <libyul/Dialect.h>
+#include <libyul/SideEffects.h>
 
 #include <boost/algorithm/cxx11/none_of.hpp>
 
@@ -37,10 +39,12 @@ UnusedPruner::UnusedPruner(
 	Dialect const& _dialect,
 	Block& _ast,
 	bool _allowMSizeOptimization,
+	map<YulString, SideEffects> const* _functionSideEffects,
 	set<YulString> const& _externallyUsedFunctions
 ):
 	m_dialect(_dialect),
-	m_allowMSizeOptimization(_allowMSizeOptimization)
+	m_allowMSizeOptimization(_allowMSizeOptimization),
+	m_functionSideEffects(_functionSideEffects)
 {
 	m_references = ReferencesCounter::countReferences(_ast);
 	for (auto const& f: _externallyUsedFunctions)
@@ -88,7 +92,10 @@ void UnusedPruner::operator()(Block& _block)
 			{
 				if (!varDecl.value)
 					statement = Block{std::move(varDecl.location), {}};
-				else if (SideEffectsCollector(m_dialect, *varDecl.value).sideEffectFree(m_allowMSizeOptimization))
+				else if (
+					SideEffectsCollector(m_dialect, *varDecl.value, m_functionSideEffects).
+					sideEffectFree(m_allowMSizeOptimization)
+				)
 				{
 					subtractReferences(ReferencesCounter::countReferences(*varDecl.value));
 					statement = Block{std::move(varDecl.location), {}};
@@ -104,7 +111,10 @@ void UnusedPruner::operator()(Block& _block)
 		else if (statement.type() == typeid(ExpressionStatement))
 		{
 			ExpressionStatement& exprStmt = boost::get<ExpressionStatement>(statement);
-			if (SideEffectsCollector(m_dialect, exprStmt.expression).sideEffectFree(m_allowMSizeOptimization))
+			if (
+				SideEffectsCollector(m_dialect, exprStmt.expression, m_functionSideEffects).
+				sideEffectFree(m_allowMSizeOptimization)
+			)
 			{
 				subtractReferences(ReferencesCounter::countReferences(exprStmt.expression));
 				statement = Block{std::move(exprStmt.location), {}};
@@ -120,26 +130,31 @@ void UnusedPruner::runUntilStabilised(
 	Dialect const& _dialect,
 	Block& _ast,
 	bool _allowMSizeOptimization,
+	map<YulString, SideEffects> const* _functionSideEffects,
 	set<YulString> const& _externallyUsedFunctions
 )
 {
 	while (true)
 	{
-		UnusedPruner pruner(_dialect, _ast, _allowMSizeOptimization, _externallyUsedFunctions);
+		UnusedPruner pruner(
+			_dialect, _ast, _allowMSizeOptimization, _functionSideEffects,
+							_externallyUsedFunctions);
 		pruner(_ast);
 		if (!pruner.shouldRunAgain())
 			return;
 	}
 }
 
-void UnusedPruner::runUntilStabilised(
+void UnusedPruner::runUntilStabilisedOnFullAST(
 	Dialect const& _dialect,
 	Block& _ast,
 	set<YulString> const& _externallyUsedFunctions
 )
 {
+	map<YulString, SideEffects> functionSideEffects =
+		SideEffectsPropagator::sideEffects(_dialect, CallGraphGenerator::callGraph(_ast));
 	bool allowMSizeOptimization = !MSizeFinder::containsMSize(_dialect, _ast);
-	runUntilStabilised(_dialect, _ast, allowMSizeOptimization, _externallyUsedFunctions);
+	runUntilStabilised(_dialect, _ast, allowMSizeOptimization, &functionSideEffects, _externallyUsedFunctions);
 }
 
 void UnusedPruner::runUntilStabilised(

libyul/optimiser/UnusedPruner.h

@@ -29,6 +29,7 @@
 namespace yul
 {
 struct Dialect;
+struct SideEffects;
 
 /**
  * Optimisation stage that removes unused variables and functions and also
@@ -50,6 +51,7 @@ public:
 		Dialect const& _dialect,
 		Block& _ast,
 		bool _allowMSizeOptimization,
+		std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,
 		std::set<YulString> const& _externallyUsedFunctions = {}
 	);
 	UnusedPruner(
@@ -70,10 +72,15 @@ public:
 		Dialect const& _dialect,
 		Block& _ast,
 		bool _allowMSizeOptimization,
+		std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,
 		std::set<YulString> const& _externallyUsedFunctions = {}
 	);
 
-	static void runUntilStabilised(
+	/// Run the pruner until the code does not change anymore.
+	/// The provided block has to be a full AST.
+	/// The pruner itself determines if msize is used and which user-defined functions
+	/// are side-effect free.
+	static void runUntilStabilisedOnFullAST(
 		Dialect const& _dialect,
 		Block& _ast,
 		std::set<YulString> const& _externallyUsedFunctions = {}
@@ -97,6 +104,7 @@ private:
 
 	Dialect const& m_dialect;
 	bool m_allowMSizeOptimization = false;
+	std::map<YulString, SideEffects> const* m_functionSideEffects = nullptr;
 	bool m_shouldRunAgain = false;
 	std::map<YulString, size_t> m_references;
 };

test/libyul/YulOptimizerTest.cpp

@@ -222,7 +222,7 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 		ForLoopInitRewriter{}(*m_ast);
 		CommonSubexpressionEliminator::run(*m_dialect, *m_ast);
 		ExpressionSimplifier::run(*m_dialect, *m_ast);
-		UnusedPruner::runUntilStabilised(*m_dialect, *m_ast);
+		UnusedPruner::runUntilStabilisedOnFullAST(*m_dialect, *m_ast);
 		DeadCodeEliminator{*m_dialect}(*m_ast);
 		ExpressionJoiner::run(*m_ast);
 		ExpressionJoiner::run(*m_ast);
@@ -230,7 +230,7 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 	else if (m_optimizerStep == "unusedPruner")
 	{
 		disambiguate();
-		UnusedPruner::runUntilStabilised(*m_dialect, *m_ast);
+		UnusedPruner::runUntilStabilisedOnFullAST(*m_dialect, *m_ast);
 	}
 	else if (m_optimizerStep == "deadCodeEliminator")
 	{
@@ -267,7 +267,7 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 
 		LoadResolver::run(*m_dialect, *m_ast);
 
-		UnusedPruner::runUntilStabilised(*m_dialect, *m_ast);
+		UnusedPruner::runUntilStabilisedOnFullAST(*m_dialect, *m_ast);
 		ExpressionJoiner::run(*m_ast);
 		ExpressionJoiner::run(*m_ast);
 	}
@@ -301,7 +301,7 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 		// reverse SSA
 		SSAReverser::run(*m_ast);
 		CommonSubexpressionEliminator::run(*m_dialect, *m_ast);
-		UnusedPruner::runUntilStabilised(*m_dialect, *m_ast);
+		UnusedPruner::runUntilStabilisedOnFullAST(*m_dialect, *m_ast);
 	}
 	else if (m_optimizerStep == "stackCompressor")
 	{

test/libyul/yulOptimizerTests/unusedPruner/movable_user_defined_function.yul

@@ -0,0 +1,13 @@
+{
+    function f(x) -> t {
+        let b := 7
+    }
+    function g(x) -> t {
+        t := x
+    }
+    let x := f(g(2))
+}
+// ====
+// step: unusedPruner
+// ----
+// { }

test/tools/yulopti.cpp

@@ -32,6 +32,7 @@
 
 #include <libyul/optimiser/BlockFlattener.h>
 #include <libyul/optimiser/Disambiguator.h>
+#include <libyul/optimiser/CallGraphGenerator.h>
 #include <libyul/optimiser/CommonSubexpressionEliminator.h>
 #include <libyul/optimiser/ControlFlowSimplifier.h>
 #include <libyul/optimiser/NameCollector.h>
@@ -54,6 +55,7 @@
 #include <libyul/optimiser/SSATransform.h>
 #include <libyul/optimiser/StackCompressor.h>
 #include <libyul/optimiser/StructuralSimplifier.h>
+#include <libyul/optimiser/Semantics.h>
 #include <libyul/optimiser/VarDeclInitializer.h>
 #include <libyul/optimiser/VarNameCleaner.h>
 
@@ -187,7 +189,7 @@ public:
 				(ControlFlowSimplifier{m_dialect})(*m_ast);
 				break;
 			case 'u':
-				UnusedPruner::runUntilStabilised(m_dialect, *m_ast);
+				UnusedPruner::runUntilStabilisedOnFullAST(m_dialect, *m_ast);
 				break;
 			case 'D':
 				DeadCodeEliminator{m_dialect}(*m_ast);