Merge pull request #5416 from ethereum/develop

Merge develop into release for 0.5.0

1 files changed, 215 insertions, 0 deletions

diff --git a/libyul/optimiser/DataFlowAnalyzer.cpp b/libyul/optimiser/DataFlowAnalyzer.cpp
new file mode 100644
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--- /dev/null
+++ b/libyul/optimiser/DataFlowAnalyzer.cpp
@@ -0,0 +1,215 @@
+/*(
+	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/>.
+*/
+/**
+ * Base class to perform data flow analysis during AST walks.
+ * Tracks assignments and is used as base class for both Rematerialiser and
+ * Common Subexpression Eliminator.
+ */
+
+#include <libyul/optimiser/DataFlowAnalyzer.h>
+
+#include <libyul/optimiser/NameCollector.h>
+#include <libyul/optimiser/Semantics.h>
+#include <libyul/Exceptions.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libdevcore/CommonData.h>
+
+#include <boost/range/adaptor/reversed.hpp>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+
+void DataFlowAnalyzer::operator()(Assignment& _assignment)
+{
+	set<YulString> names;
+	for (auto const& var: _assignment.variableNames)
+		names.emplace(var.name);
+	assertThrow(_assignment.value, OptimizerException, "");
+	visit(*_assignment.value);
+	handleAssignment(names, _assignment.value.get());
+}
+
+void DataFlowAnalyzer::operator()(VariableDeclaration& _varDecl)
+{
+	set<YulString> names;
+	for (auto const& var: _varDecl.variables)
+		names.emplace(var.name);
+	m_variableScopes.back().variables += names;
+	if (_varDecl.value)
+		visit(*_varDecl.value);
+	handleAssignment(names, _varDecl.value.get());
+}
+
+void DataFlowAnalyzer::operator()(If& _if)
+{
+	ASTModifier::operator()(_if);
+
+	Assignments assignments;
+	assignments(_if.body);
+	clearValues(assignments.names());
+}
+
+void DataFlowAnalyzer::operator()(Switch& _switch)
+{
+	visit(*_switch.expression);
+	set<YulString> assignedVariables;
+	for (auto& _case: _switch.cases)
+	{
+		(*this)(_case.body);
+		Assignments assignments;
+		assignments(_case.body);
+		assignedVariables += assignments.names();
+		// This is a little too destructive, we could retain the old values.
+		clearValues(assignments.names());
+	}
+	clearValues(assignedVariables);
+}
+
+void DataFlowAnalyzer::operator()(FunctionDefinition& _fun)
+{
+	// Save all information. We might rather reinstantiate this class,
+	// but this could be difficult if it is subclassed.
+	map<YulString, Expression const*> value;
+	map<YulString, set<YulString>> references;
+	map<YulString, set<YulString>> referencedBy;
+	m_value.swap(value);
+	m_references.swap(references);
+	m_referencedBy.swap(referencedBy);
+	pushScope(true);
+
+	for (auto const& parameter: _fun.parameters)
+		m_variableScopes.back().variables.emplace(parameter.name);
+	for (auto const& var: _fun.returnVariables)
+		m_variableScopes.back().variables.emplace(var.name);
+	ASTModifier::operator()(_fun);
+
+	popScope();
+	m_value.swap(value);
+	m_references.swap(references);
+	m_referencedBy.swap(referencedBy);
+}
+
+void DataFlowAnalyzer::operator()(ForLoop& _for)
+{
+	// Special scope handling of the pre block.
+	pushScope(false);
+	for (auto& statement: _for.pre.statements)
+		visit(statement);
+
+	Assignments assignments;
+	assignments(_for.body);
+	assignments(_for.post);
+	clearValues(assignments.names());
+
+	visit(*_for.condition);
+	(*this)(_for.body);
+	(*this)(_for.post);
+
+	clearValues(assignments.names());
+	popScope();
+}
+
+void DataFlowAnalyzer::operator()(Block& _block)
+{
+	size_t numScopes = m_variableScopes.size();
+	pushScope(false);
+	ASTModifier::operator()(_block);
+	popScope();
+	assertThrow(numScopes == m_variableScopes.size(), OptimizerException, "");
+}
+
+void DataFlowAnalyzer::handleAssignment(set<YulString> const& _variables, Expression* _value)
+{
+	clearValues(_variables);
+
+	MovableChecker movableChecker;
+	if (_value)
+		movableChecker.visit(*_value);
+	if (_variables.size() == 1)
+	{
+		YulString name = *_variables.begin();
+		// Expression has to be movable and cannot contain a reference
+		// to the variable that will be assigned to.
+		if (_value && movableChecker.movable() && !movableChecker.referencedVariables().count(name))
+			m_value[name] = _value;
+	}
+
+	auto const& referencedVariables = movableChecker.referencedVariables();
+	for (auto const& name: _variables)
+	{
+		m_references[name] = referencedVariables;
+		for (auto const& ref: referencedVariables)
+			m_referencedBy[ref].emplace(name);
+	}
+}
+
+void DataFlowAnalyzer::pushScope(bool _functionScope)
+{
+	m_variableScopes.emplace_back(_functionScope);
+}
+
+void DataFlowAnalyzer::popScope()
+{
+	clearValues(std::move(m_variableScopes.back().variables));
+	m_variableScopes.pop_back();
+}
+
+void DataFlowAnalyzer::clearValues(set<YulString> _variables)
+{
+	// All variables that reference variables to be cleared also have to be
+	// cleared, but not recursively, since only the value of the original
+	// variables changes. Example:
+	// let a := 1
+	// let b := a
+	// let c := b
+	// let a := 2
+	// add(b, c)
+	// In the last line, we can replace c by b, but not b by a.
+	//
+	// This cannot be easily tested since the substitutions will be done
+	// one by one on the fly, and the last line will just be add(1, 1)
+
+	// Clear variables that reference variables to be cleared.
+	for (auto const& name: _variables)
+		for (auto const& ref: m_referencedBy[name])
+			_variables.emplace(ref);
+
+	// Clear the value and update the reference relation.
+	for (auto const& name: _variables)
+		m_value.erase(name);
+	for (auto const& name: _variables)
+	{
+		for (auto const& ref: m_references[name])
+			m_referencedBy[ref].erase(name);
+		m_references[name].clear();
+	}
+}
+
+bool DataFlowAnalyzer::inScope(YulString _variableName) const
+{
+	for (auto const& scope: m_variableScopes | boost::adaptors::reversed)
+	{
+		if (scope.variables.count(_variableName))
+			return true;
+		if (scope.isFunction)
+			return false;
+	}
+	return false;
+}