Conditional simplifier.

libyul/optimiser/ConditionalSimplifier.cpp

@@ -0,0 +1,92 @@
+/*
+	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/ConditionalSimplifier.h>
+#include <libyul/optimiser/Semantics.h>
+#include <libyul/AsmData.h>
+#include <libyul/Utilities.h>
+#include <libyul/optimiser/NameCollector.h>
+#include <libdevcore/CommonData.h>
+#include <libdevcore/Visitor.h>
+
+using namespace std;
+using namespace dev;
+using namespace yul;
+
+void ConditionalSimplifier::operator()(Switch& _switch)
+{
+	visit(*_switch.expression);
+	if (_switch.expression->type() != typeid(Identifier))
+	{
+		ASTModifier::operator()(_switch);
+		return;
+	}
+	YulString expr = boost::get<Identifier>(*_switch.expression).name;
+	for (auto& _case: _switch.cases)
+	{
+		if (_case.value)
+		{
+			(*this)(*_case.value);
+			_case.body.statements.insert(_case.body.statements.begin(),
+				Assignment{
+					_case.body.location,
+					{Identifier{_case.body.location, expr}},
+					make_unique<Expression>(*_case.value)
+				}
+			);
+		}
+		(*this)(_case.body);
+	}
+}
+
+void ConditionalSimplifier::operator()(Block& _block)
+{
+	iterateReplacing(
+		_block.statements,
+		[&](Statement& _s) -> std::optional<vector<Statement>>
+		{
+			visit(_s);
+			if (_s.type() == typeid(If))
+			{
+				If& _if = boost::get<If>(_s);
+				if (
+					_if.condition->type() == typeid(Identifier) &&
+					!_if.body.statements.empty() &&
+					TerminationFinder(m_dialect).controlFlowKind(_if.body.statements.back()) !=
+						TerminationFinder::ControlFlow::FlowOut
+				)
+				{
+					YulString condition = boost::get<Identifier>(*_if.condition).name;
+					langutil::SourceLocation location = _if.location;
+					return make_vector<Statement>(
+						std::move(_s),
+						Assignment{
+							location,
+							{Identifier{location, condition}},
+							make_unique<Expression>(Literal{
+								location,
+								LiteralKind::Number,
+								"0"_yulstring,
+								{}
+							})
+						}
+					);
+				}
+			}
+			return {};
+		}
+	);
+}

libyul/optimiser/ConditionalSimplifier.h

@@ -0,0 +1,71 @@
+/*
+	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/>.
+*/
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/optimiser/OptimiserStep.h>
+#include <libyul/Dialect.h>
+#include <libdevcore/Common.h>
+
+namespace yul
+{
+
+/**
+ * Conditional simplifier.
+ *
+ * Inserts assignments to condition variables if the value can be determined
+ * from the control-flow.
+ *
+ * Destroys SSA form.
+ *
+ * Currently, this tool is very limited, mostly because we do not yet have support
+ * for boolean types. Since conditions only check for expressions being nonzero,
+ * we cannot assign a specific value.
+ *
+ * Current features:
+ *  - switch cases: insert "<condition> := <caseLabel>"
+ *  - after if statement with terminating control-flow, insert "<condition> := 0"
+ *
+ * Future features:
+ *  - allow replacements by "1"
+ *  - take termination of user-defined functions into account
+ *
+ * Works best with SSA form and if dead code removal has run before.
+ *
+ * Prerequisite: Disambiguator.
+ */
+class ConditionalSimplifier: public ASTModifier
+{
+public:
+	static constexpr char const* name{"ConditionalSimplifier"};
+	static void run(OptimiserStepContext& _context, Block& _ast)
+	{
+		ConditionalSimplifier{_context.dialect}(_ast);
+	}
+
+	using ASTModifier::operator();
+	void operator()(Switch& _switch) override;
+	void operator()(Block& _block) override;
+
+private:
+	explicit ConditionalSimplifier(Dialect const& _dialect):
+		m_dialect(_dialect)
+	{}
+	Dialect const& m_dialect;
+};
+
+}

libyul/optimiser/Suite.cpp

@@ -25,6 +25,7 @@
 #include <libyul/optimiser/BlockFlattener.h>
 #include <libyul/optimiser/CallGraphGenerator.h>
 #include <libyul/optimiser/ControlFlowSimplifier.h>
+#include <libyul/optimiser/ConditionalSimplifier.h>
 #include <libyul/optimiser/DeadCodeEliminator.h>
 #include <libyul/optimiser/FunctionGrouper.h>
 #include <libyul/optimiser/FunctionHoister.h>
@@ -36,6 +37,7 @@
 #include <libyul/optimiser/ForLoopConditionIntoBody.h>
 #include <libyul/optimiser/ForLoopConditionOutOfBody.h>
 #include <libyul/optimiser/ForLoopInitRewriter.h>
+#include <libyul/optimiser/ForLoopConditionIntoBody.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/UnusedPruner.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
@@ -96,6 +98,7 @@ void OptimiserSuite::run(
 		EquivalentFunctionCombiner::name,
 		UnusedPruner::name,
 		BlockFlattener::name,
+		ConditionalSimplifier::name,
 		ControlFlowSimplifier::name,
 		LiteralRematerialiser::name,
 		StructuralSimplifier::name,
@@ -130,9 +133,12 @@ void OptimiserSuite::run(
 		}
 
 		{
-			// still in SSA, perform structural simplification
+			// perform structural simplification
 			suite.runSequence({
+				CommonSubexpressionEliminator::name,
+				ConditionalSimplifier::name,
 				LiteralRematerialiser::name,
+				StructuralSimplifier::name,
 				ForLoopConditionOutOfBody::name,
 				ControlFlowSimplifier::name,
 				StructuralSimplifier::name,
@@ -200,6 +206,8 @@ void OptimiserSuite::run(
 		{
 			// SSA plus simplify
 			suite.runSequence({
+				ConditionalSimplifier::name,
+				CommonSubexpressionEliminator::name,
 				SSATransform::name,
 				RedundantAssignEliminator::name,
 				RedundantAssignEliminator::name,
@@ -315,6 +323,7 @@ map<string, unique_ptr<OptimiserStep>> const& OptimiserSuite::allSteps()
 		instance = optimiserStepCollection<
 			BlockFlattener,
 			CommonSubexpressionEliminator,
+			ConditionalSimplifier,
 			ControlFlowSimplifier,
 			DeadCodeEliminator,
 			EquivalentFunctionCombiner,