Merge pull request #5655 from ethereum/removeUnassignedVarDefs

Add variable declaration initializer.

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

@@ -1,126 +0,0 @@
-/*
-	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/VarDeclPropagator.h>
-#include <libyul/AsmData.h>
-#include <libdevcore/CommonData.h>
-#include <boost/range/algorithm_ext/erase.hpp>
-#include <algorithm>
-#include <map>
-
-using namespace std;
-using namespace dev;
-using namespace yul;
-
-void VarDeclPropagator::operator()(Block& _block)
-{
-	map<YulString, TypedName> outerEmptyVarDecls;
-	map<YulString, TypedName> outerLazyInitializedVarDecls;
-	swap(m_emptyVarDecls, outerEmptyVarDecls);
-	swap(m_lazyInitializedVarDecls, outerLazyInitializedVarDecls);
-
-	ASTModifier::operator()(_block);
-
-	iterateReplacing(
-		_block.statements,
-		[this](Statement& _stmt) -> boost::optional<vector<Statement>>
-		{
-			if (_stmt.type() == typeid(VariableDeclaration))
-			{
-				VariableDeclaration& varDecl = boost::get<VariableDeclaration>(_stmt);
-				boost::remove_erase_if(
-					varDecl.variables,
-					[&](TypedName const& _typedName) { return m_lazyInitializedVarDecls.count(_typedName.name); }
-				);
-				if (varDecl.variables.empty())
-					return vector<Statement>{};
-				else
-					return {};
-			}
-			else if (_stmt.type() == typeid(Assignment))
-			{
-				Assignment& assignment = boost::get<Assignment>(_stmt);
-				if (isFullyLazyInitialized(assignment.variableNames))
-					return vector<Statement>{recreateVariableDeclaration(assignment)};
-				else
-					return {};
-			}
-			else
-				return {};
-		}
-	);
-
-	swap(m_emptyVarDecls, outerEmptyVarDecls);
-	swap(m_lazyInitializedVarDecls, outerLazyInitializedVarDecls);
-}
-
-void VarDeclPropagator::operator()(VariableDeclaration& _varDecl)
-{
-	if (_varDecl.value)
-		visit(*_varDecl.value);
-	else
-		for (TypedName const& typedName: _varDecl.variables)
-			m_emptyVarDecls[typedName.name] = typedName;
-}
-
-void VarDeclPropagator::operator()(Assignment& _assignment)
-{
-	visit(*_assignment.value);
-
-	if (allVarNamesUninitialized(_assignment.variableNames))
-		for (Identifier const& ident: _assignment.variableNames)
-			m_lazyInitializedVarDecls[ident.name] = m_emptyVarDecls[ident.name];
-
-	for (Identifier& name: _assignment.variableNames)
-		(*this)(name);
-}
-
-void VarDeclPropagator::operator()(Identifier& _ident)
-{
-	m_emptyVarDecls.erase(_ident.name);
-}
-
-bool VarDeclPropagator::allVarNamesUninitialized(vector<Identifier> const& _variableNames) const
-{
-	return all_of(
-		begin(_variableNames),
-		end(_variableNames),
-		[&](Identifier const& _ident) -> bool { return m_emptyVarDecls.count(_ident.name); }
-	);
-}
-
-bool VarDeclPropagator::isFullyLazyInitialized(vector<Identifier> const& _variableNames) const
-{
-	return all_of(
-		begin(_variableNames),
-		end(_variableNames),
-		[&](Identifier const& ident) -> bool { return m_lazyInitializedVarDecls.count(ident.name); }
-	);
-}
-
-VariableDeclaration VarDeclPropagator::recreateVariableDeclaration(Assignment& _assignment)
-{
-	TypedNameList variables;
-
-	for (Identifier const& varName: _assignment.variableNames)
-	{
-		variables.emplace_back(move(m_lazyInitializedVarDecls.at(varName.name)));
-		m_lazyInitializedVarDecls.erase(varName.name);
-	}
-
-	return VariableDeclaration{move(_assignment.location), move(variables), std::move(_assignment.value)};
-}

libyul/optimiser/VarDeclPropagator.h

@@ -1,60 +0,0 @@
-/*
-	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>
-#include <libyul/Exceptions.h>
-#include <libyul/AsmDataForward.h>
-#include <vector>
-#include <set>
-#include <map>
-
-namespace yul
-{
-
-/**
- * Rewrites Assignment statements into VariableDeclaration when the assignment's LHS
- * variables had no value yet.
- *
- * It recursively walks through the AST and moves each declaration of variables to
- * the first assignment within the same block (if possible)..
- */
-class VarDeclPropagator: public ASTModifier
-{
-public:
-	using ASTModifier::operator();
-	void operator()(Block& _block) override;
-	void operator()(VariableDeclaration& _varDecl) override;
-	void operator()(Assignment& _assignment) override;
-	void operator()(Identifier& _ident) override;
-
-private:
-	bool allVarNamesUninitialized(std::vector<Identifier> const& _variableNames) const;
-	bool isFullyLazyInitialized(std::vector<Identifier> const& _variableNames) const;
-	VariableDeclaration recreateVariableDeclaration(Assignment& _assignment);
-
-private:
-	/// Holds a list of variables from current Block that have no value assigned yet.
-	std::map<YulString, TypedName> m_emptyVarDecls;
-
-	/// Holds a list variables (and their TypedName) within the current block.
-	std::map<YulString, TypedName> m_lazyInitializedVarDecls;
-};
-
-}

test/libyul/YulOptimizerTest.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")
+	else if (m_optimizerStep == "varDeclInitializer")
-	{
+		VarDeclInitializer{}(*m_ast);
-		disambiguate();
-		VarDeclPropagator{}(*m_ast);
-	}
 	else if (m_optimizerStep == "forLoopInitRewriter")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/fullInliner/double_inline.yul

@@ -9,14 +9,14 @@
 // {
 //     {
 //         let f_a := calldataload(0)
-//         let f_b
+//         let f_b := 0
-//         let f_c
+//         let f_c := 0
 //         f_b := sload(mload(f_a))
 //         f_c := 3
 //         let b3 := f_b
 //         let f_a_2 := f_c
-//         let f_b_3
+//         let f_b_3 := 0
-//         let f_c_4
+//         let f_c_4 := 0
 //         f_b_3 := sload(mload(f_a_2))
 //         f_c_4 := 3
 //         let b4 := f_b_3

test/libyul/yulOptimizerTests/fullInliner/inside_condition.yul

@@ -14,7 +14,7 @@
 //     {
 //         let _2 := mload(0)
 //         let f_a := mload(1)
-//         let f_r
+//         let f_r := 0
 //         f_a := mload(f_a)
 //         f_r := add(f_a, calldatasize())
 //         if gt(f_r, _2)

test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul

@@ -23,7 +23,7 @@
 //         let a2 := 2
 //         let r := f(a_1)
 //         let f_a := a2
-//         let f_b
+//         let f_b := 0
 //         let f_x := mload(f_a)
 //         f_b := sload(f_x)
 //         let f_y := add(f_a, f_x)
@@ -31,7 +31,7 @@
 //         let t := f_b
 //         let a3
 //         let f_a_3 := a3
-//         let f_b_4
+//         let f_b_4 := 0
 //         let f_x_5 := mload(f_a_3)
 //         f_b_4 := sload(f_x_5)
 //         let f_y_6 := add(f_a_3, f_x_5)

test/libyul/yulOptimizerTests/fullInliner/large_function_single_use.yul

@@ -15,7 +15,7 @@
 // {
 //     {
 //         let f_a := mload(1)
-//         let f_b
+//         let f_b := 0
 //         let f_x := mload(f_a)
 //         f_b := sload(f_x)
 //         let f_c := 3

test/libyul/yulOptimizerTests/fullInliner/long_names.yul

@@ -13,7 +13,7 @@
 //     {
 //         let verylongvariablename2_1 := 3
 //         let verylongfu_verylongvariablename := verylongvariablename2_1
-//         let verylongfu_verylongvariablename2
+//         let verylongfu_verylongvariablename2 := 0
 //         verylongfu_verylongvariablename2 := add(verylongfu_verylongvariablename, verylongfu_verylongvariablename)
 //         mstore(0, verylongfu_verylongvariablename2)
 //         mstore(1, verylongvariablename2_1)

test/libyul/yulOptimizerTests/fullInliner/move_up_rightwards_argument.yul

@@ -15,7 +15,7 @@
 //         let f_a := mload(2)
 //         let f_b := _6
 //         let f_c := _4
-//         let f_x
+//         let f_x := 0
 //         f_x := add(f_a, f_b)
 //         f_x := mul(f_x, f_c)
 //         let _10 := add(f_x, _2)

test/libyul/yulOptimizerTests/fullInliner/multi_fun.yul

@@ -9,11 +9,11 @@
 //     {
 //         let _1 := 7
 //         let f_a := 3
-//         let f_x
+//         let f_x := 0
 //         f_x := add(f_a, f_a)
 //         let g_b := f_x
 //         let g_c := _1
-//         let g_y
+//         let g_y := 0
 //         g_y := mul(mload(g_c), f(g_b))
 //         let y_1 := g_y
 //     }
@@ -24,7 +24,7 @@
 //     function g(b, c) -> y
 //     {
 //         let f_a_6 := b
-//         let f_x_7
+//         let f_x_7 := 0
 //         f_x_7 := add(f_a_6, f_a_6)
 //         y := mul(mload(c), f_x_7)
 //     }

test/libyul/yulOptimizerTests/fullInliner/multi_fun_callback.yul

@@ -37,7 +37,7 @@
 //     function f(x)
 //     {
 //         mstore(0, x)
-//         let h_t
+//         let h_t := 0
 //         h_t := 2
 //         mstore(7, h_t)
 //         let g_x_1 := 10

test/libyul/yulOptimizerTests/fullInliner/multi_return.yul

@@ -11,8 +11,8 @@
 // {
 //     {
 //         let f_a := mload(0)
-//         let f_x
+//         let f_x := 0
-//         let f_y
+//         let f_y := 0
 //         f_x := mul(f_a, f_a)
 //         f_y := add(f_a, f_x)
 //         let r := f_x

test/libyul/yulOptimizerTests/fullInliner/no_inline_into_big_function.yul

@@ -19,25 +19,25 @@
 //     function g() -> x_1
 //     {
 //         let f_a := 2
-//         let f_b
+//         let f_b := 0
 //         f_b := sload(mload(f_a))
 //         let f_a_20 := f_b
-//         let f_b_21
+//         let f_b_21 := 0
 //         f_b_21 := sload(mload(f_a_20))
 //         let f_a_23 := f_b_21
-//         let f_b_24
+//         let f_b_24 := 0
 //         f_b_24 := sload(mload(f_a_23))
 //         let f_a_26 := f_b_24
-//         let f_b_27
+//         let f_b_27 := 0
 //         f_b_27 := sload(mload(f_a_26))
 //         let f_a_29 := f_b_27
-//         let f_b_30
+//         let f_b_30 := 0
 //         f_b_30 := sload(mload(f_a_29))
 //         let f_a_32 := f_b_30
-//         let f_b_33
+//         let f_b_33 := 0
 //         f_b_33 := sload(mload(f_a_32))
 //         let f_a_35 := f_b_33
-//         let f_b_36
+//         let f_b_36 := 0
 //         f_b_36 := sload(mload(f_a_35))
 //         x_1 := f(f(f(f(f(f(f(f(f(f(f(f(f_b_36))))))))))))
 //     }

test/libyul/yulOptimizerTests/fullInliner/no_inline_into_big_global_context.yul

@@ -12,25 +12,25 @@
 // {
 //     {
 //         let f_a := 2
-//         let f_b
+//         let f_b := 0
 //         f_b := sload(mload(f_a))
 //         let f_a_20 := f_b
-//         let f_b_21
+//         let f_b_21 := 0
 //         f_b_21 := sload(mload(f_a_20))
 //         let f_a_23 := f_b_21
-//         let f_b_24
+//         let f_b_24 := 0
 //         f_b_24 := sload(mload(f_a_23))
 //         let f_a_26 := f_b_24
-//         let f_b_27
+//         let f_b_27 := 0
 //         f_b_27 := sload(mload(f_a_26))
 //         let f_a_29 := f_b_27
-//         let f_b_30
+//         let f_b_30 := 0
 //         f_b_30 := sload(mload(f_a_29))
 //         let f_a_32 := f_b_30
-//         let f_b_33
+//         let f_b_33 := 0
 //         f_b_33 := sload(mload(f_a_32))
 //         let f_a_35 := f_b_33
-//         let f_b_36
+//         let f_b_36 := 0
 //         f_b_36 := sload(mload(f_a_35))
 //         let x_1 := f(f(f(f(f(f(f(f(f(f(f(f(f_b_36))))))))))))
 //     }

test/libyul/yulOptimizerTests/fullInliner/not_inside_for.yul

@@ -14,7 +14,7 @@
 //     {
 //         for {
 //             let f_a := 0
-//             let f_r
+//             let f_r := 0
 //             sstore(f_a, 0)
 //             f_r := f_a
 //             let x := f_r
@@ -22,14 +22,14 @@
 //         f(x)
 //         {
 //             let f_a_3 := x
-//             let f_r_4
+//             let f_r_4 := 0
 //             sstore(f_a_3, 0)
 //             f_r_4 := f_a_3
 //             x := f_r_4
 //         }
 //         {
 //             let f_a_6 := x
-//             let f_r_7
+//             let f_r_7 := 0
 //             sstore(f_a_6, 0)
 //             f_r_7 := f_a_6
 //             let t := f_r_7

test/libyul/yulOptimizerTests/fullInliner/pop_result.yul

@@ -14,7 +14,7 @@
 //     {
 //         let _1 := 2
 //         let f_a := 7
-//         let f_x
+//         let f_x := 0
 //         let f_r := mul(f_a, f_a)
 //         f_x := add(f_r, f_r)
 //         pop(add(f_x, _1))

test/libyul/yulOptimizerTests/fullInliner/simple.yul

@@ -11,7 +11,7 @@
 //     {
 //         let _2 := mload(7)
 //         let f_a := sload(mload(2))
-//         let f_x
+//         let f_x := 0
 //         let f_r := mul(f_a, f_a)
 //         f_x := add(f_r, f_r)
 //         let y := add(f_x, _2)

test/libyul/yulOptimizerTests/fullSuite/abi_example1.yul

@@ -463,12 +463,11 @@
 //         let _2 := 0
 //         let _485 := mload(_2)
 //         let abi_encode_pos := _1
-//         let abi_encode_end_67_610
 //         let abi_encode_length_68 := mload(_485)
 //         mstore(_1, abi_encode_length_68)
 //         abi_encode_pos := 64
 //         let abi_encode_srcPtr := add(_485, _1)
-//         let abi_encode_i_69 := abi_encode_end_67_610
+//         let abi_encode_i_69 := _2
 //         for {
 //         }
 //         lt(abi_encode_i_69, abi_encode_length_68)
@@ -476,21 +475,21 @@
 //             abi_encode_i_69 := add(abi_encode_i_69, 1)
 //         }
 //         {
-//             let _857 := mload(abi_encode_srcPtr)
+//             let _863 := mload(abi_encode_srcPtr)
-//             let abi_encode_pos_71_965 := abi_encode_pos
+//             let abi_encode_pos_71_971 := abi_encode_pos
-//             let abi_encode_length_72_966 := 0x3
+//             let abi_encode_length_72_972 := 0x3
-//             let abi_encode_srcPtr_73_967 := _857
+//             let abi_encode_srcPtr_73_973 := _863
-//             let abi_encode_i_74_968 := _2
+//             let abi_encode_i_74_974 := _2
 //             for {
 //             }
-//             lt(abi_encode_i_74_968, abi_encode_length_72_966)
+//             lt(abi_encode_i_74_974, abi_encode_length_72_972)
 //             {
-//                 abi_encode_i_74_968 := add(abi_encode_i_74_968, 1)
+//                 abi_encode_i_74_974 := add(abi_encode_i_74_974, 1)
 //             }
 //             {
-//                 mstore(abi_encode_pos_71_965, and(mload(abi_encode_srcPtr_73_967), 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF))
+//                 mstore(abi_encode_pos_71_971, and(mload(abi_encode_srcPtr_73_973), 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF))
-//                 abi_encode_srcPtr_73_967 := add(abi_encode_srcPtr_73_967, _1)
+//                 abi_encode_srcPtr_73_973 := add(abi_encode_srcPtr_73_973, _1)
-//                 abi_encode_pos_71_965 := add(abi_encode_pos_71_965, _1)
+//                 abi_encode_pos_71_971 := add(abi_encode_pos_71_971, _1)
 //             }
 //             abi_encode_srcPtr := add(abi_encode_srcPtr, _1)
 //             abi_encode_pos := add(abi_encode_pos, 0x60)

test/libyul/yulOptimizerTests/varDeclInitializer/ambiguous.yul

@@ -0,0 +1,29 @@
+{
+  // This component does not need the disambiguator
+  function f() -> x, y {
+    let a, b
+    mstore(a, b)
+    let d
+    d := 2
+  }
+  let a
+  a := 4
+  let b := 2
+  let x, y := f()
+}
+// ----
+// varDeclInitializer
+// {
+//     function f() -> x, y
+//     {
+//         let a := 0
+//         let b := 0
+//         mstore(a, b)
+//         let d := 0
+//         d := 2
+//     }
+//     let a := 0
+//     a := 4
+//     let b := 2
+//     let x, y := f()
+// }

test/libyul/yulOptimizerTests/varDeclInitializer/inside_func.yul

@@ -0,0 +1,24 @@
+{
+  function f() -> x, y {
+    let a, b
+    mstore(a, b)
+    let d
+    d := 2
+  }
+  let r
+  r := 4
+}
+// ----
+// varDeclInitializer
+// {
+//     function f() -> x, y
+//     {
+//         let a := 0
+//         let b := 0
+//         mstore(a, b)
+//         let d := 0
+//         d := 2
+//     }
+//     let r := 0
+//     r := 4
+// }

test/libyul/yulOptimizerTests/varDeclInitializer/multi.yul

@@ -0,0 +1,14 @@
+{
+  let x, y, z
+  let a
+  let b
+}
+// ----
+// varDeclInitializer
+// {
+//     let x := 0
+//     let y := 0
+//     let z := 0
+//     let a := 0
+//     let b := 0
+// }

test/libyul/yulOptimizerTests/varDeclInitializer/multi_assign.yul

@@ -0,0 +1,21 @@
+{
+  function f() -> x, y {
+    let a, b := f()
+	let u
+  }
+  let r
+  let s := 3
+  let t
+}
+// ----
+// varDeclInitializer
+// {
+//     function f() -> x, y
+//     {
+//         let a, b := f()
+//         let u := 0
+//     }
+//     let r := 0
+//     let s := 3
+//     let t := 0
+// }

test/libyul/yulOptimizerTests/varDeclInitializer/simple.yul

@@ -0,0 +1,8 @@
+{
+  let a
+}
+// ----
+// varDeclInitializer
+// {
+//     let a := 0
+// }

test/libyul/yulOptimizerTests/varDeclPropagator/init_assignment_inside_if.yul

@@ -1,17 +0,0 @@
-{
-  let a := 4
-  let x
-  if a {
-    x := 2
-  }
-}
-// ----
-// varDeclPropagator
-// {
-//     let a := 4
-//     let x
-//     if a
-//     {
-//         x := 2
-//     }
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/multi_assignment_vardecl.yul

@@ -1,13 +0,0 @@
-{
-  function f() -> a, b, c {}
-  let x, y, z
-  z, x, y := f()
-}
-// ----
-// varDeclPropagator
-// {
-//     function f() -> a, b, c
-//     {
-//     }
-//     let z, x, y := f()
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/overwrite.yul

@@ -1,11 +0,0 @@
-{
-  let a
-  a := 4
-  a := 5
-}
-// ----
-// varDeclPropagator
-// {
-//     let a := 4
-//     a := 5
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/rewrite_removes_unused_var.yul

@@ -1,10 +0,0 @@
-{
-  let a, b
-  a := mload(0)
-}
-// ----
-// varDeclPropagator
-// {
-//     let b
-//     let a := mload(0)
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/simple1.yul

@@ -1,9 +0,0 @@
-{
-  let f
-  f := mload(0)
-}
-// ----
-// varDeclPropagator
-// {
-//     let f := mload(0)
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/split_assign_splits_vardecl.yul

@@ -1,11 +0,0 @@
-{
-  let a, b
-  a := mload(0)
-  b := mload(1)
-}
-// ----
-// varDeclPropagator
-// {
-//     let a := mload(0)
-//     let b := mload(1)
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/use_before_init.yul

@@ -1,12 +0,0 @@
-{
-	let b
-	let a := b
-	b := 1
-}
-// ----
-// varDeclPropagator
-// {
-//     let b
-//     let a := b
-//     b := 1
-// }

test/libyul/yulOptimizerTests/varDeclPropagator/use_doesnt_rewrite.yul

@@ -1,16 +0,0 @@
-{
-  function f(x) {}
-  let a
-  f(a)
-  a := 4
-}
-// ----
-// varDeclPropagator
-// {
-//     function f(x)
-//     {
-//     }
-//     let a
-//     f(a)
-//     a := 4
-// }

test/tools/yulopti.cpp

@@ -47,7 +47,7 @@
 #include <libyul/optimiser/RedundantAssignEliminator.h>
 #include <libyul/optimiser/SSATransform.h>
 #include <libyul/optimiser/StructuralSimplifier.h>
-#include <libyul/optimiser/VarDeclPropagator.h>
+#include <libyul/optimiser/VarDeclInitializer.h>
 
 #include <libyul/backends/evm/EVMDialect.h>
 
@@ -125,7 +125,7 @@ public:
 				m_nameDispenser = make_shared<NameDispenser>(*m_ast);
 				disambiguated = true;
 			}
-			cout << "(q)quit/(f)flatten/(c)se/propagate var(d)ecls/(x)plit/(j)oin/(g)rouper/(h)oister/" << endl;
+			cout << "(q)quit/(f)flatten/(c)se/initialize var(d)ecls/(x)plit/(j)oin/(g)rouper/(h)oister/" << endl;
 			cout << "  (e)xpr inline/(i)nline/(s)implify/(u)nusedprune/ss(a) transform/" << endl;
 			cout << "  (r)edundant assign elim./re(m)aterializer/f(o)r-loop-pre-rewriter/" << endl;
 			cout << "  s(t)ructural simplifier? " << endl;
@@ -146,7 +146,7 @@ public:
 				(CommonSubexpressionEliminator{})(*m_ast);
 				break;
 			case 'd':
-				(VarDeclPropagator{})(*m_ast);
+				(VarDeclInitializer{})(*m_ast);
 				break;
 			case 'x':
 				ExpressionSplitter{*m_nameDispenser}(*m_ast);