Control flow side-effects for user-defined functions.

Author: chriseth

libsolidity/analysis/ControlFlowBuilder.cpp

@@ -533,14 +533,14 @@ void ControlFlowBuilder::operator()(yul::FunctionCall const& _functionCall)
 	yul::ASTWalker::operator()(_functionCall);
 
 	if (auto const *builtinFunction = m_inlineAssembly->dialect().builtin(_functionCall.functionName.name))
-		if (builtinFunction->controlFlowSideEffects.terminates)
-		{
-			if (builtinFunction->controlFlowSideEffects.reverts)
-				connect(m_currentNode, m_revertNode);
-			else
-				connect(m_currentNode, m_transactionReturnNode);
+	{
+		if (builtinFunction->controlFlowSideEffects.canTerminate)
+			connect(m_currentNode, m_transactionReturnNode);
+		if (builtinFunction->controlFlowSideEffects.canRevert)
+			connect(m_currentNode, m_revertNode);
+		if (!builtinFunction->controlFlowSideEffects.canContinue)
 			m_currentNode = newLabel();
-		}
+	}
 }
 
 void ControlFlowBuilder::operator()(yul::FunctionDefinition const&)

libyul/CMakeLists.txt

@@ -34,6 +34,9 @@ add_library(yul
 	AssemblyStack.cpp
 	CompilabilityChecker.cpp
 	CompilabilityChecker.h
+	ControlFlowSideEffects.h
+	ControlFlowSideEffectsCollector.cpp
+	ControlFlowSideEffectsCollector.h
 	Dialect.cpp
 	Dialect.h
 	Exceptions.h

libyul/ControlFlowSideEffects.h

@@ -18,22 +18,25 @@
 
 #pragma once
 
-#include <set>
-
 namespace solidity::yul
 {
 
 /**
- * Side effects of code related to control flow.
+ * Side effects of a user-defined or builtin function.
  */
 struct ControlFlowSideEffects
 {
-	/// If true, this code terminates the control flow.
-	/// State may or may not be reverted as indicated by the ``reverts`` flag.
-	bool terminates = false;
-	/// If true, this code reverts all state changes in the transaction.
-	/// Whenever this is true, ``terminates`` has to be true as well.
-	bool reverts = false;
+	/// If true, the function contains at least one reachable branch that terminates successfully.
+	bool canTerminate = false;
+	/// If true, the function contains at least one reachable branch that reverts.
+	bool canRevert = false;
+	/// If true, the function has a regular outgoing control-flow.
+	bool canContinue = true;
+
+	bool terminatesOrReverts() const
+	{
+		return (canTerminate || canRevert) && !canContinue;
+	}
 };
 
 }

libyul/ControlFlowSideEffectsCollector.cpp

@@ -0,0 +1,269 @@
+/*
+	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/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+
+#include <libyul/ControlFlowSideEffectsCollector.h>
+
+#include <libyul/optimiser/FunctionDefinitionCollector.h>
+
+#include <libyul/AST.h>
+#include <libyul/Dialect.h>
+
+#include <libsolutil/Common.h>
+#include <libsolutil/Algorithms.h>
+
+#include <range/v3/view/reverse.hpp>
+#include <range/v3/algorithm/find_if.hpp>
+
+using namespace std;
+using namespace solidity::yul;
+
+
+ControlFlowBuilder::ControlFlowBuilder(Block const& _ast)
+{
+	for (auto const& statement: _ast.statements)
+		if (auto const* function = get_if<FunctionDefinition>(&statement))
+			(*this)(*function);
+}
+
+void ControlFlowBuilder::operator()(FunctionCall const& _functionCall)
+{
+	walkVector(_functionCall.arguments | ranges::views::reverse);
+	newConnectedNode();
+	m_currentNode->functionCall = _functionCall.functionName.name;
+}
+
+void ControlFlowBuilder::operator()(If const& _if)
+{
+	visit(*_if.condition);
+	ControlFlowNode* node = m_currentNode;
+	(*this)(_if.body);
+	newConnectedNode();
+	node->successors.emplace_back(m_currentNode);
+}
+
+void ControlFlowBuilder::operator()(Switch const& _switch)
+{
+	visit(*_switch.expression);
+	ControlFlowNode* initialNode = m_currentNode;
+	ControlFlowNode* finalNode = newNode();
+
+	if (_switch.cases.back().value)
+		initialNode->successors.emplace_back(finalNode);
+
+	for (Case const& case_: _switch.cases)
+	{
+		m_currentNode = initialNode;
+		(*this)(case_.body);
+		newConnectedNode();
+		m_currentNode->successors.emplace_back(finalNode);
+	}
+	m_currentNode = finalNode;
+}
+
+void ControlFlowBuilder::operator()(FunctionDefinition const& _function)
+{
+	ScopedSaveAndRestore currentNode(m_currentNode, nullptr);
+	ScopedSaveAndRestore leaveNode(m_leave, nullptr);
+	ScopedSaveAndRestore breakNode(m_break, nullptr);
+	ScopedSaveAndRestore continueNode(m_continue, nullptr);
+
+	FunctionFlow flow;
+	flow.exit = newNode();
+	m_currentNode = newNode();
+	flow.entry = m_currentNode;
+	newConnectedNode();
+	m_leave = flow.exit;
+
+	(*this)(_function.body);
+
+	m_currentNode->successors.emplace_back(flow.exit);
+
+	m_functionFlows[_function.name] = move(flow);
+}
+
+void ControlFlowBuilder::operator()(ForLoop const& _for)
+{
+	ScopedSaveAndRestore scopedBreakNode(m_break, nullptr);
+	ScopedSaveAndRestore scopedContinueNode(m_continue, nullptr);
+
+	(*this)(_for.pre);
+
+	ControlFlowNode* breakNode = newNode();
+	m_break = breakNode;
+	ControlFlowNode* continueNode = newNode();
+	m_continue = continueNode;
+
+	newConnectedNode();
+	ControlFlowNode* loopNode = m_currentNode;
+	visit(*_for.condition);
+	m_currentNode->successors.emplace_back(m_break);
+	newConnectedNode();
+
+	(*this)(_for.body);
+
+	m_currentNode->successors.emplace_back(m_continue);
+	m_currentNode = continueNode;
+
+	(*this)(_for.post);
+	m_currentNode->successors.emplace_back(loopNode);
+
+	m_currentNode = breakNode;
+}
+
+void ControlFlowBuilder::operator()(Break const&)
+{
+	m_currentNode->successors.emplace_back(m_break);
+	m_currentNode = newNode();
+}
+
+void ControlFlowBuilder::operator()(Continue const&)
+{
+	m_currentNode->successors.emplace_back(m_continue);
+	m_currentNode = newNode();
+}
+
+void ControlFlowBuilder::operator()(Leave const&)
+{
+	m_currentNode->successors.emplace_back(m_leave);
+	m_currentNode = newNode();
+}
+
+void ControlFlowBuilder::newConnectedNode()
+{
+	ControlFlowNode* node = newNode();
+	m_currentNode->successors.emplace_back(node);
+	m_currentNode = node;
+}
+
+ControlFlowNode* ControlFlowBuilder::newNode()
+{
+	m_nodes.emplace_back(make_shared<ControlFlowNode>());
+	return m_nodes.back().get();
+}
+
+
+ControlFlowSideEffectsCollector::ControlFlowSideEffectsCollector(
+	Dialect const& _dialect,
+	Block const& _ast
+):
+	m_dialect(_dialect),
+	m_cfgBuilder(_ast)
+{
+	for (auto&& [name, flow]: m_cfgBuilder.functionFlows())
+	{
+		recordReachabilityAndQueue(name, flow.entry);
+		m_functionSideEffects[name] = {false, false, false};
+	}
+
+	// Process functions while we have progress. For now, we are only interested
+	// in `canContinue`.
+	bool progress = true;
+	while (progress)
+	{
+		progress = false;
+		for (auto const& fun: m_pendingNodes)
+			if (processFunction(fun.first))
+				progress = true;
+	}
+
+	// No progress anymore: All remaining nodes are calls
+	// to functions that always recurse.
+	// If we have not set `canContinue` by now, the function's exit
+	// is not reachable.
+
+	for (auto&& [functionName, calls]: m_functionCalls)
+	{
+		ControlFlowSideEffects& sideEffects = m_functionSideEffects[functionName];
+		auto _visit = [&, visited = std::set<YulString>{}](YulString _function, auto&& _recurse) mutable {
+			if (sideEffects.canTerminate && sideEffects.canRevert)
+				return;
+			if (!visited.insert(_function).second)
+				return;
+
+			ControlFlowSideEffects const* calledSideEffects = nullptr;
+			if (BuiltinFunction const* f = _dialect.builtin(_function))
+				calledSideEffects = &f->controlFlowSideEffects;
+			else
+				calledSideEffects = &m_functionSideEffects.at(_function);
+
+			if (calledSideEffects->canTerminate)
+				sideEffects.canTerminate = true;
+			if (calledSideEffects->canRevert)
+				sideEffects.canRevert = true;
+
+			if (m_functionCalls.count(_function))
+				for (YulString callee: m_functionCalls.at(_function))
+					_recurse(callee, _recurse);
+		};
+		for (auto const& call: calls)
+			_visit(call, _visit);
+	}
+
+}
+
+bool ControlFlowSideEffectsCollector::processFunction(YulString _name)
+{
+	bool progress = false;
+	while (ControlFlowNode const* node = nextProcessableNode(_name))
+	{
+		if (node == m_cfgBuilder.functionFlows().at(_name).exit)
+		{
+			m_functionSideEffects[_name].canContinue = true;
+			return true;
+		}
+		for (ControlFlowNode const* s: node->successors)
+			recordReachabilityAndQueue(_name, s);
+
+		progress = true;
+	}
+	return progress;
+}
+
+ControlFlowNode const* ControlFlowSideEffectsCollector::nextProcessableNode(YulString _functionName)
+{
+	std::list<ControlFlowNode const*>& nodes = m_pendingNodes[_functionName];
+	auto it = ranges::find_if(nodes, [this](ControlFlowNode const* _node) {
+		return !_node->functionCall || sideEffects(*_node->functionCall).canContinue;
+	});
+	if (it == nodes.end())
+		return nullptr;
+
+	ControlFlowNode const* node = *it;
+	m_pendingNodes[_functionName].erase(it);
+	return node;
+}
+
+ControlFlowSideEffects const& ControlFlowSideEffectsCollector::sideEffects(YulString _functionName) const
+{
+	if (auto const* builtin = m_dialect.builtin(_functionName))
+		return builtin->controlFlowSideEffects;
+	else
+		return m_functionSideEffects.at(_functionName);
+}
+
+void ControlFlowSideEffectsCollector::recordReachabilityAndQueue(
+	YulString _functionName,
+	ControlFlowNode const* _node
+)
+{
+	if (_node->functionCall)
+		m_functionCalls[_functionName].insert(*_node->functionCall);
+	if (m_processedNodes[_functionName].insert(_node).second)
+		m_pendingNodes[_functionName].push_front(_node);
+}
+