Merge pull request ethereum#5655 from ethereum/removeUnassignedVarDefs

Add variable declaration initializer.

Author: chriseth

libyul/CMakeLists.txt

@@ -43,6 +43,6 @@ add_library(yul
 	optimiser/SyntacticalEquality.cpp
 	optimiser/UnusedPruner.cpp
 	optimiser/Utilities.cpp
-	optimiser/VarDeclPropagator.cpp
+	optimiser/VarDeclInitializer.cpp
 )
 target_link_libraries(yul PUBLIC evmasm devcore langutil)

libyul/optimiser/FullInliner.cpp

@@ -168,6 +168,8 @@ vector<Statement> InlineModifier::performInline(Statement& _statement, FunctionC
 
 	m_driver.tentativelyUpdateCodeSize(function->name, m_currentFunction);
 
+	static Expression const zero{Literal{{}, LiteralKind::Number, YulString{"0"}, {}}};
+
 	// helper function to create a new variable that is supposed to model
 	// an existing variable.
 	auto newVariable = [&](TypedName const& _existingVariable, Expression* _value) {
@@ -176,6 +178,8 @@ vector<Statement> InlineModifier::performInline(Statement& _statement, FunctionC
 		VariableDeclaration varDecl{_funCall.location, {{_funCall.location, newName, _existingVariable.type}}, {}};
 		if (_value)
 			varDecl.value = make_shared<Expression>(std::move(*_value));
+		else
+			varDecl.value = make_shared<Expression>(zero);
 		newStatements.emplace_back(std::move(varDecl));
 	};
 

libyul/optimiser/Suite.cpp

@@ -21,6 +21,7 @@
 #include <libyul/optimiser/Suite.h>
 
 #include <libyul/optimiser/Disambiguator.h>
+#include <libyul/optimiser/VarDeclInitializer.h>
 #include <libyul/optimiser/FunctionGrouper.h>
 #include <libyul/optimiser/FunctionHoister.h>
 #include <libyul/optimiser/ExpressionSplitter.h>
@@ -35,7 +36,6 @@
 #include <libyul/optimiser/SSATransform.h>
 #include <libyul/optimiser/StructuralSimplifier.h>
 #include <libyul/optimiser/RedundantAssignEliminator.h>
-#include <libyul/optimiser/VarDeclPropagator.h>
 #include <libyul/AsmAnalysisInfo.h>
 #include <libyul/AsmData.h>
 #include <libyul/AsmPrinter.h>
@@ -56,6 +56,7 @@ void OptimiserSuite::run(
 
 	Block ast = boost::get<Block>(Disambiguator(_analysisInfo, reservedIdentifiers)(_ast));
 
+	(VarDeclInitializer{})(ast);
 	(FunctionHoister{})(ast);
 	(FunctionGrouper{})(ast);
 	(ForLoopInitRewriter{})(ast);
@@ -68,7 +69,6 @@ void OptimiserSuite::run(
 		ExpressionSplitter{dispenser}(ast);
 		SSATransform::run(ast, dispenser);
 		RedundantAssignEliminator::run(ast);
-		VarDeclPropagator{}(ast);
 		RedundantAssignEliminator::run(ast);
 
 		CommonSubexpressionEliminator{}(ast);
@@ -95,27 +95,22 @@ void OptimiserSuite::run(
 		RedundantAssignEliminator::run(ast);
 		CommonSubexpressionEliminator{}(ast);
 		FullInliner{ast, dispenser}.run();
-		VarDeclPropagator{}(ast);
 		SSATransform::run(ast, dispenser);
 		RedundantAssignEliminator::run(ast);
-		VarDeclPropagator{}(ast);
 		RedundantAssignEliminator::run(ast);
 		ExpressionSimplifier::run(ast);
 		StructuralSimplifier{}(ast);
 		CommonSubexpressionEliminator{}(ast);
 		SSATransform::run(ast, dispenser);
 		RedundantAssignEliminator::run(ast);
-		VarDeclPropagator{}(ast);
 		RedundantAssignEliminator::run(ast);
 		UnusedPruner::runUntilStabilised(ast, reservedIdentifiers);
 	}
 	ExpressionJoiner::run(ast);
-	VarDeclPropagator{}(ast);
 	UnusedPruner::runUntilStabilised(ast);
 	ExpressionJoiner::run(ast);
 	UnusedPruner::runUntilStabilised(ast);
 	ExpressionJoiner::run(ast);
-	VarDeclPropagator{}(ast);
 	UnusedPruner::runUntilStabilised(ast);
 	ExpressionJoiner::run(ast);
 	UnusedPruner::runUntilStabilised(ast);

libyul/optimiser/VarDeclInitializer.cpp

@@ -0,0 +1,56 @@
+/*
+	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/VarDeclInitializer.h>
+#include <libyul/AsmData.h>
+
+#include <libdevcore/CommonData.h>
+#include <libdevcore/Visitor.h>
+
+using namespace std;
+using namespace dev;
+using namespace yul;
+
+void VarDeclInitializer::operator()(Block& _block)
+{
+	ASTModifier::operator()(_block);
+
+	static Expression const zero{Literal{{}, LiteralKind::Number, YulString{"0"}, {}}};
+
+	using OptionalStatements = boost::optional<vector<Statement>>;
+	GenericFallbackReturnsVisitor<OptionalStatements, VariableDeclaration> visitor{
+		[](VariableDeclaration& _varDecl) -> OptionalStatements
+		{
+			if (_varDecl.value)
+				return {};
+			else if (_varDecl.variables.size() == 1)
+			{
+				_varDecl.value = make_shared<Expression>(zero);
+				return {};
+			}
+			else
+			{
+				OptionalStatements ret{vector<Statement>{}};
+				langutil::SourceLocation loc{std::move(_varDecl.location)};
+				for (auto& var: _varDecl.variables)
+					ret->push_back(VariableDeclaration{loc, {std::move(var)}, make_shared<Expression>(zero)});
+				return ret;
+			}
+		}
+	};
+	iterateReplacing(_block.statements, boost::apply_visitor(visitor));
+}

libyul/optimiser/VarDeclInitializer.h

@@ -0,0 +1,38 @@
+/*
+	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/AsmDataForward.h>
+#include <libyul/optimiser/ASTWalker.h>
+
+namespace yul
+{
+
+/**
+ * Rewrites variable declarations so that all of them are initialized.
+ * Declarations like ``let x, y`` are split into multiple declaration
+ * statements.
+ * Only supports initializing with the zero literal for now.
+ */
+class VarDeclInitializer: public ASTModifier
+{
+public:
+	void operator()(Block& _block) override;
+};
+
+}

libyul/optimiser/VarDeclPropagator.cpp

@@ -22,7 +22,7 @@
 #include <test/Options.h>
 
 #include <libyul/optimiser/BlockFlattener.h>
-#include <libyul/optimiser/VarDeclPropagator.h>
+#include <libyul/optimiser/VarDeclInitializer.h>
 #include <libyul/optimiser/Disambiguator.h>
 #include <libyul/optimiser/CommonSubexpressionEliminator.h>
 #include <libyul/optimiser/NameCollector.h>
@@ -107,11 +107,8 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 		disambiguate();
 		BlockFlattener{}(*m_ast);
 	}
-	else if (m_optimizerStep == "varDeclPropagator")
-	{
-		disambiguate();
-		VarDeclPropagator{}(*m_ast);
-	}
+	else if (m_optimizerStep == "varDeclInitializer")
+		VarDeclInitializer{}(*m_ast);
 	else if (m_optimizerStep == "forLoopInitRewriter")
 	{
 		disambiguate();