[Yul] Prune functions that call each other but are otherwise unreferenced

libyul/optimiser/CircularReferencesPruner.cpp

@@ -0,0 +1,61 @@
+/*
+	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 <libyul/optimiser/CircularReferencesPruner.h>
+
+#include <libyul/optimiser/CallGraphGenerator.h>
+#include <libyul/optimiser/OptimizerUtilities.h>
+#include <libyul/AsmData.h>
+
+#include <libsolutil/Algorithms.h>
+
+using namespace std;
+using namespace solidity::yul;
+
+void CircularReferencesPruner::run(OptimiserStepContext& _context, Block& _ast)
+{
+	CircularReferencesPruner{_context.reservedIdentifiers}(_ast);
+}
+
+void CircularReferencesPruner::operator()(Block& _block)
+{
+	set<YulString> functionsToKeep =
+		functionsCalledFromOutermostContext(CallGraphGenerator::callGraph(_block));
+
+	for (auto&& statement: _block.statements)
+		if (holds_alternative<FunctionDefinition>(statement))
+		{
+			FunctionDefinition const& funDef = std::get<FunctionDefinition>(statement);
+			if (!functionsToKeep.count(funDef.name))
+				statement = Block{};
+		}
+
+	removeEmptyBlocks(_block);
+}
+
+set<YulString> CircularReferencesPruner::functionsCalledFromOutermostContext(CallGraph const& _callGraph)
+{
+	set<YulString> verticesToTraverse = m_reservedIdentifiers;
+	verticesToTraverse.insert(YulString(""));
+
+	return util::BreadthFirstSearch<YulString>{{verticesToTraverse.begin(), verticesToTraverse.end()}}.run(
+		[&_callGraph](YulString _function, auto&& _addChild) {
+			if (_callGraph.functionCalls.count(_function))
+				for (auto const& callee: _callGraph.functionCalls.at(_function))
+					if (_callGraph.functionCalls.count(callee))
+						_addChild(callee);
+		}).visited;
+}