Merge pull request #9397 from ethereum/function-unused-parameter

[YUL] Remove unused function parameters

Changelog.md

@@ -1,5 +1,12 @@
 ### 0.7.2 (unreleased)
 
+Language Features:
+
+
+Compiler Features:
+ * Yul Optimizer: Prune unused parameters in functions.
+
+Bugfixes:
 
 
 ### 0.7.1 (2020-09-02)

libsolidity/interface/OptimiserSettings.h

@@ -41,7 +41,7 @@ struct OptimiserSettings
 
 			// should have good "compilability" property here.
 
-			"eul"                      // Run functional expression inliner
+			"Tpeul"                    // Run functional expression inliner
 			"xarulrul"                 // Prune a bit more in SSA
 			"xarrcL"                   // Turn into SSA again and simplify
 			"gvif"                     // Run full inliner

libsolutil/CommonData.h

@@ -209,6 +209,13 @@ std::map<V, K> invertMap(std::map<K, V> const& originalMap)
 	return inverseMap;
 }
 
+/// Returns a set of keys of a map.
+template <typename K, typename V>
+std::set<K> keys(std::map<K, V> const& _map)
+{
+	return applyMap(_map, [](auto const& _elem) { return _elem.first; }, std::set<K>{});
+}
+
 // String conversion functions, mainly to/from hex/nibble/byte representations.
 
 enum class WhenError

libyul/CMakeLists.txt

@@ -156,6 +156,9 @@ add_library(yul
 	optimiser/SyntacticalEquality.h
 	optimiser/TypeInfo.cpp
 	optimiser/TypeInfo.h
+	optimiser/UnusedFunctionParameterPruner.cpp
+	optimiser/UnusedFunctionParameterPruner.h
+	optimiser/UnusedFunctionsCommon.h
 	optimiser/UnusedPruner.cpp
 	optimiser/UnusedPruner.h
 	optimiser/VarDeclInitializer.cpp

libyul/optimiser/NameDisplacer.h

@@ -60,6 +60,8 @@ public:
 	void operator()(FunctionCall& _funCall) override;
 	void operator()(Block& _block) override;
 
+	std::map<YulString, YulString> const& translations() const { return m_translations; }
+
 protected:
 	/// Check if the newly introduced identifier @a _name has to be replaced.
 	void checkAndReplaceNew(YulString& _name);

libyul/optimiser/Suite.cpp

@@ -42,6 +42,7 @@
 #include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/ForLoopConditionIntoBody.h>
 #include <libyul/optimiser/Rematerialiser.h>
+#include <libyul/optimiser/UnusedFunctionParameterPruner.h>
 #include <libyul/optimiser/UnusedPruner.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
 #include <libyul/optimiser/CommonSubexpressionEliminator.h>
@@ -185,6 +186,7 @@ map<string, unique_ptr<OptimiserStep>> const& OptimiserSuite::allSteps()
 			SSAReverser,
 			SSATransform,
 			StructuralSimplifier,
+			UnusedFunctionParameterPruner,
 			UnusedPruner,
 			VarDeclInitializer
 		>();
@@ -221,6 +223,7 @@ map<string, char> const& OptimiserSuite::stepNameToAbbreviationMap()
 		{SSAReverser::name,                   'V'},
 		{SSATransform::name,                  'a'},
 		{StructuralSimplifier::name,          't'},
+		{UnusedFunctionParameterPruner::name, 'p'},
 		{UnusedPruner::name,                  'u'},
 		{VarDeclInitializer::name,            'd'},
 	};

libyul/optimiser/UnusedFunctionParameterPruner.cpp

@@ -0,0 +1,127 @@
+/*
+	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
+/**
+ * UnusedFunctionParameterPruner: Optimiser step that removes unused parameters from function
+ * definition.
+ */
+
+#include <libyul/optimiser/UnusedFunctionParameterPruner.h>
+#include <libyul/optimiser/UnusedFunctionsCommon.h>
+#include <libyul/optimiser/OptimiserStep.h>
+#include <libyul/optimiser/NameCollector.h>
+#include <libyul/optimiser/NameDisplacer.h>
+#include <libyul/optimiser/NameDispenser.h>
+#include <libyul/YulString.h>
+#include <libyul/AsmData.h>
+
+#include <libsolutil/CommonData.h>
+
+#include <boost/algorithm/cxx11/all_of.hpp>
+
+#include <optional>
+#include <variant>
+
+using namespace std;
+using namespace solidity::util;
+using namespace solidity::yul;
+using namespace solidity::yul::unusedFunctionsCommon;
+
+void UnusedFunctionParameterPruner::run(OptimiserStepContext& _context, Block& _ast)
+{
+	map<YulString, size_t> references = ReferencesCounter::countReferences(_ast);
+	auto used = [&](auto v) -> bool { return references.count(v.name); };
+
+	// Function name and a pair of boolean masks, the first corresponds to parameters and the second
+	// corresponds to returnVariables.
+	//
+	// For the first vector in the pair, a value `false` at index `i` indicates that the function
+	// argument at index `i` in `FunctionDefinition::parameters` is unused inside the function body.
+	//
+	// Similarly for the second vector in the pair, a value `false` at index `i` indicates that the
+	// return parameter at index `i` in `FunctionDefinition::returnVariables` is unused inside
+	// function body.
+	map<YulString, pair<vector<bool>, vector<bool>>> usedParametersAndReturnVariables;
+
+	// Step 1 of UnusedFunctionParameterPruner: Find functions whose parameters (both arguments and
+	// return-parameters) are not used in its body.
+	for (auto const& statement: _ast.statements)
+		if (holds_alternative<FunctionDefinition>(statement))
+		{
+			FunctionDefinition const& f = std::get<FunctionDefinition>(statement);
+
+			if (tooSimpleToBePruned(f) || boost::algorithm::all_of(f.parameters + f.returnVariables, used))
+				continue;
+
+			usedParametersAndReturnVariables[f.name] = {
+				applyMap(f.parameters, used),
+				applyMap(f.returnVariables, used)
+			};
+		}
+
+	set<YulString> functionNamesToFree = util::keys(usedParametersAndReturnVariables);
+
+	// Step 2 of UnusedFunctionParameterPruner: Renames the function and replaces all references to
+	// the function, say `f`, by its new name, say `f_1`.
+	NameDisplacer replace{_context.dispenser, functionNamesToFree};
+	replace(_ast);
+
+	// Inverse-Map of the above translations. In the above example, this will store an element with
+	// key `f_1` and value `f`.
+	std::map<YulString, YulString> newToOriginalNames = invertMap(replace.translations());
+
+	// Step 3 of UnusedFunctionParameterPruner: introduce a new function in the block with body of
+	// the old one. Replace the body of the old one with a function call to the new one with reduced
+	// parameters.
+	//
+	// For example: introduce a new 'linking' function `f` with the same the body as `f_1`, but with
+	// reduced parameters, i.e., `function f() -> y { y := 1 }`. Now replace the body of `f_1` with
+	// a call to `f`, i.e., `f_1(x) -> y { y := f() }`.
+	iterateReplacing(_ast.statements, [&](Statement& _s) -> optional<vector<Statement>> {
+		if (holds_alternative<FunctionDefinition>(_s))
+		{
+			// The original function except that it has a new name (e.g., `f_1`)
+			FunctionDefinition& originalFunction = get<FunctionDefinition>(_s);
+			if (newToOriginalNames.count(originalFunction.name))
+			{
+
+				YulString linkingFunctionName = originalFunction.name;
+				YulString originalFunctionName = newToOriginalNames.at(linkingFunctionName);
+				pair<vector<bool>, vector<bool>> used =
+					usedParametersAndReturnVariables.at(originalFunctionName);
+
+				FunctionDefinition linkingFunction = createLinkingFunction(
+					originalFunction,
+					used,
+					originalFunctionName,
+					linkingFunctionName,
+					_context.dispenser
+				);
+
+				originalFunction.name = originalFunctionName;
+				originalFunction.parameters =
+					filter(originalFunction.parameters, used.first);
+				originalFunction.returnVariables =
+					filter(originalFunction.returnVariables, used.second);
+
+				return make_vector<Statement>(move(originalFunction), move(linkingFunction));
+			}
+		}
+
+		return nullopt;
+	});
+}

libyul/optimiser/UnusedFunctionParameterPruner.h

@@ -0,0 +1,52 @@
+/*
+	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
+
+#pragma once
+
+#include <libyul/optimiser/OptimiserStep.h>
+
+namespace solidity::yul
+{
+
+/**
+ * UnusedFunctionParameterPruner: Optimiser step that removes unused parameters in a function.
+ *
+ * If a parameter is unused, like `c` and `y` in, `function f(a,b,c) -> x, y { x := div(a,b) }`
+ *
+ * We remove the parameter and create a new "linking" function as follows:
+ *
+ * `function f(a,b) -> x { x := div(a,b) }`
+ * `function f2(a,b,c) -> x, y { x := f(a,b) }`
+ *
+ * and replace all references to `f` by `f2`.
+ * The inliner should be run afterwards to make sure that all references to `f2` are replaced by
+ * `f`.
+ *
+ * Prerequisites: Disambiguator, FunctionHoister, LiteralRematerialiser
+ *
+ * The step LiteralRematerialiser is not required for correctness. It helps deal with cases such as:
+ * `function f(x) -> y { revert(y, y} }` where the literal `y` will be replaced by its value `0`,
+ * allowing us to rewrite the function.
+ */
+struct UnusedFunctionParameterPruner
+{
+	static constexpr char const* name{"UnusedFunctionParameterPruner"};
+	static void run(OptimiserStepContext& _context, Block& _ast);
+};
+
+}

libyul/optimiser/UnusedFunctionsCommon.h

@@ -0,0 +1,103 @@
+/*
+	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
+#pragma once
+
+#include <libyul/optimiser/Metrics.h>
+#include <libyul/optimiser/NameDispenser.h>
+#include <libyul/AsmData.h>
+#include <libyul/Dialect.h>
+#include <libyul/Exceptions.h>
+
+#include <liblangutil/SourceLocation.h>
+
+#include <libsolutil/CommonData.h>
+
+#include <variant>
+
+namespace solidity::yul::unusedFunctionsCommon
+{
+
+template<typename T>
+std::vector<T> filter(std::vector<T> const& _vec, std::vector<bool> const& _mask)
+{
+	yulAssert(_vec.size() == _mask.size(), "");
+
+	std::vector<T> ret;
+
+	for (size_t i = 0; i < _mask.size(); ++i)
+		if (_mask[i])
+			ret.push_back(_vec[i]);
+
+	return ret;
+}
+
+/// Returns true if applying UnusedFunctionParameterPruner is not helpful or redundant because the
+/// inliner will be able to handle it anyway.
+bool tooSimpleToBePruned(FunctionDefinition const& _f)
+{
+	return _f.body.statements.size() <= 1 && CodeSize::codeSize(_f.body) <= 1;
+}
+
+FunctionDefinition createLinkingFunction(
+	FunctionDefinition const& _original,
+	std::pair<std::vector<bool>, std::vector<bool>> const& _usedParametersAndReturns,
+	YulString const& _originalFunctionName,
+	YulString const& _linkingFunctionName,
+	NameDispenser& _nameDispenser
+)
+{
+	auto generateTypedName = [&](TypedName t)
+	{
+		return TypedName{
+			t.location,
+			_nameDispenser.newName(t.name),
+			t.type
+		};
+	};
+
+	langutil::SourceLocation loc = _original.location;
+
+	FunctionDefinition linkingFunction{
+		loc,
+		_linkingFunctionName,
+		util::applyMap(_original.parameters, generateTypedName),
+		util::applyMap(_original.returnVariables, generateTypedName),
+		{loc, {}} // body
+	};
+
+	FunctionCall call{loc, Identifier{loc, _originalFunctionName}, {}};
+	for (auto const& p: filter(linkingFunction.parameters, _usedParametersAndReturns.first))
+		call.arguments.emplace_back(Identifier{loc, p.name});
+
+	Assignment assignment{loc, {}, nullptr};
+
+	for (auto const& r: filter(linkingFunction.returnVariables, _usedParametersAndReturns.second))
+		assignment.variableNames.emplace_back(Identifier{loc, r.name});
+
+	if (assignment.variableNames.empty())
+		linkingFunction.body.statements.emplace_back(ExpressionStatement{loc, std::move(call)});
+	else
+	{
+		assignment.value = std::make_unique<Expression>(std::move(call));
+		linkingFunction.body.statements.emplace_back(std::move(assignment));
+	}
+
+	return linkingFunction;
+}
+
+}

test/cmdlineTests/evm_to_wasm_break/output

@@ -31,9 +31,10 @@ object "object" {
             let x_6 := x_2
             let x_7 := x_3
             let _2 := 1
-            let _3:i32 := i32.eqz(i32.eqz(i64.eqz(i64.or(i64.or(_1, _1), i64.or(_1, _2)))))
+            let _3 := i64.or(_1, _1)
+            let _4:i32 := i32.eqz(i32.eqz(i64.eqz(i64.or(_3, i64.or(_1, _2)))))
             for { }
-            i32.eqz(_3)
+            i32.eqz(_4)
             {
                 let x_8, x_9, x_10, x_11 := add(x_4, x_5, x_6, x_7, _1, _1, _1, _2)
                 x_4 := x_8
@@ -42,13 +43,10 @@ object "object" {
                 x_7 := x_11
             }
             {
-                let _4, _5, _6, _7 := lt(x_4, x_5, x_6, x_7, _1, _1, _1, 10)
+                let _5, _6, _7, _8 := iszero_170_789(_1, _1, _1, lt_172(x_4, x_5, x_6, x_7, _1, _1, _1, 10))
-                let _8, _9, _10, _11 := iszero(_4, _5, _6, _7)
+                if i32.eqz(i64.eqz(i64.or(i64.or(_5, _6), i64.or(_7, _8)))) { break }
-                if i32.eqz(i64.eqz(i64.or(i64.or(_8, _9), i64.or(_10, _11)))) { break }
+                if i32.eqz(i64.eqz(i64.or(_3, i64.or(_1, eq(x_4, x_5, x_6, x_7, _1, _1, _1, 2))))) { break }
-                let _12, _13, _14, _15 := eq(x_4, x_5, x_6, x_7, _1, _1, _1, 2)
+                if i32.eqz(i64.eqz(i64.or(_3, i64.or(_1, eq(x_4, x_5, x_6, x_7, _1, _1, _1, 4))))) { continue }
-                if i32.eqz(i64.eqz(i64.or(i64.or(_12, _13), i64.or(_14, _15)))) { break }
-                let _16, _17, _18, _19 := eq(x_4, x_5, x_6, x_7, _1, _1, _1, 4)
-                if i32.eqz(i64.eqz(i64.or(i64.or(_16, _17), i64.or(_18, _19)))) { continue }
             }
             sstore(_1, _1, _1, _1, x_4, x_5, x_6, x_7)
         }
@@ -69,11 +67,11 @@ object "object" {
             let r1_1, carry_2 := add_carry(x1, y1, carry_1)
             r1 := r1_1
         }
-        function iszero(x1, x2, x3, x4) -> r1, r2, r3, r4
+        function iszero_170_789(x1, x2, x3, x4) -> r1, r2, r3, r4
         {
             r4 := i64.extend_i32_u(i64.eqz(i64.or(i64.or(x1, x2), i64.or(x3, x4))))
         }
-        function eq(x1, x2, x3, x4, y1, y2, y3, y4) -> r1, r2, r3, r4
+        function eq(x1, x2, x3, x4, y1, y2, y3, y4) -> r4
         {
             if i64.eq(x1, y1)
             {
@@ -89,7 +87,7 @@ object "object" {
             case 1:i32 { r := 0xffffffff:i32 }
             default { r := i64.ne(a, b) }
         }
-        function lt(x1, x2, x3, x4, y1, y2, y3, y4) -> z1, z2, z3, z4
+        function lt_172(x1, x2, x3, x4, y1, y2, y3, y4) -> z4
         {
             let z:i32 := false
             switch cmp(x1, y1)
@@ -154,7 +152,7 @@ object "object" {
 
 
 Binary representation:
-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
 
 Text representation:
 (module
@@ -177,23 +175,12 @@ Text representation:
     (local $x_6 i64)
     (local $x_7 i64)
     (local $_2 i64)
-    (local $_3 i32)
+    (local $_3 i64)
-    (local $_4 i64)
+    (local $_4 i32)
     (local $_5 i64)
     (local $_6 i64)
     (local $_7 i64)
     (local $_8 i64)
-    (local $_9 i64)
-    (local $_10 i64)
-    (local $_11 i64)
-    (local $_12 i64)
-    (local $_13 i64)
-    (local $_14 i64)
-    (local $_15 i64)
-    (local $_16 i64)
-    (local $_17 i64)
-    (local $_18 i64)
-    (local $_19 i64)
     (local $x_8 i64)
     (local $x_9 i64)
     (local $x_10 i64)
@@ -212,46 +199,26 @@ Text representation:
         (local.set $x_6 (local.get $x_2))
         (local.set $x_7 (local.get $x_3))
         (local.set $_2 (i64.const 1))
-        (local.set $_3 (i32.eqz (i32.eqz (i64.eqz (i64.or (i64.or (local.get $_1) (local.get $_1)) (i64.or (local.get $_1) (local.get $_2)))))))
+        (local.set $_3 (i64.or (local.get $_1) (local.get $_1)))
+        (local.set $_4 (i32.eqz (i32.eqz (i64.eqz (i64.or (local.get $_3) (i64.or (local.get $_1) (local.get $_2)))))))
         (block $label__3
             (loop $label__5
-                (br_if $label__3 (i32.eqz (i32.eqz (local.get $_3))))
+                (br_if $label__3 (i32.eqz (i32.eqz (local.get $_4))))
                 (block $label__4
                     (block
-                        (local.set $_4 (call $lt (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 10)))
+                        (local.set $_5 (call $iszero_170_789 (local.get $_1) (local.get $_1) (local.get $_1) (call $lt_172 (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 10))))
-                        (local.set $_5 (global.get $global_))
+                        (local.set $_6 (global.get $global_))
-                        (local.set $_6 (global.get $global__1))
+                        (local.set $_7 (global.get $global__1))
-                        (local.set $_7 (global.get $global__2))
+                        (local.set $_8 (global.get $global__2))
 
                     )
-                    (block
+                    (if (i32.eqz (i64.eqz (i64.or (i64.or (local.get $_5) (local.get $_6)) (i64.or (local.get $_7) (local.get $_8))))) (then
-                        (local.set $_8 (call $iszero (local.get $_4) (local.get $_5) (local.get $_6) (local.get $_7)))
-                        (local.set $_9 (global.get $global_))
-                        (local.set $_10 (global.get $global__1))
-                        (local.set $_11 (global.get $global__2))
-
-                    )
-                    (if (i32.eqz (i64.eqz (i64.or (i64.or (local.get $_8) (local.get $_9)) (i64.or (local.get $_10) (local.get $_11))))) (then
                         (br $label__3)
                     ))
-                    (block
+                    (if (i32.eqz (i64.eqz (i64.or (local.get $_3) (i64.or (local.get $_1) (call $eq (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 2)))))) (then
-                        (local.set $_12 (call $eq (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 2)))
-                        (local.set $_13 (global.get $global_))
-                        (local.set $_14 (global.get $global__1))
-                        (local.set $_15 (global.get $global__2))
-
-                    )
-                    (if (i32.eqz (i64.eqz (i64.or (i64.or (local.get $_12) (local.get $_13)) (i64.or (local.get $_14) (local.get $_15))))) (then
                         (br $label__3)
                     ))
-                    (block
+                    (if (i32.eqz (i64.eqz (i64.or (local.get $_3) (i64.or (local.get $_1) (call $eq (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 4)))))) (then
-                        (local.set $_16 (call $eq (local.get $x_4) (local.get $x_5) (local.get $x_6) (local.get $x_7) (local.get $_1) (local.get $_1) (local.get $_1) (i64.const 4)))
-                        (local.set $_17 (global.get $global_))
-                        (local.set $_18 (global.get $global__1))
-                        (local.set $_19 (global.get $global__2))
-
-                    )
-                    (if (i32.eqz (i64.eqz (i64.or (i64.or (local.get $_16) (local.get $_17)) (i64.or (local.get $_18) (local.get $_19))))) (then
                         (br $label__4)
                     ))
 
@@ -343,7 +310,7 @@ Text representation:
     (local.get $r1)
 )
 
-(func $iszero
+(func $iszero_170_789
     (param $x1 i64)
     (param $x2 i64)
     (param $x3 i64)
@@ -373,9 +340,6 @@ Text representation:
     (param $y3 i64)
     (param $y4 i64)
     (result i64)
-    (local $r1 i64)
-    (local $r2 i64)
-    (local $r3 i64)
     (local $r4 i64)
     (block $label__9
         (if (i64.eq (local.get $x1) (local.get $y1)) (then
@@ -389,10 +353,7 @@ Text representation:
         ))
 
     )
-    (global.set $global_ (local.get $r2))
+    (local.get $r4)
-    (global.set $global__1 (local.get $r3))
-    (global.set $global__2 (local.get $r4))
-    (local.get $r1)
 )
 
 (func $cmp
@@ -416,7 +377,7 @@ Text representation:
     (local.get $r)
 )
 
-(func $lt
+(func $lt_172
     (param $x1 i64)
     (param $x2 i64)
     (param $x3 i64)
@@ -426,9 +387,6 @@ Text representation:
     (param $y3 i64)
     (param $y4 i64)
     (result i64)
-    (local $z1 i64)
-    (local $z2 i64)
-    (local $z3 i64)
     (local $z4 i64)
     (local $z i32)
     (local $condition_12 i32)
@@ -476,10 +434,7 @@ Text representation:
         (local.set $z4 (i64.extend_i32_u (local.get $z)))
 
     )
-    (global.set $global_ (local.get $z2))
+    (local.get $z4)
-    (global.set $global__1 (local.get $z3))
-    (global.set $global__2 (local.get $z4))
-    (local.get $z1)
 )
 
 (func $calldataload

test/cmdlineTests/yul_stack_opt/input.sol

@@ -17,6 +17,21 @@
 		sstore(add(a, 10), b)
 		sstore(add(a, 11), b)
 		sstore(add(a, 12), b)
+		a3 := 1
+		b3 := 1
+		c3 := 1
+		d3 := 1
+		e3 := 1
+		f3 := 1
+		g3 := 1
+		h3 := 1
+		i3 := 1
+		j3 := 1
+		k3 := 1
+		l3 := 1
+		m3 := 1
+		o3 := 1
+		p3 := 1
 	}
 	let a1, b1, c1, d1, e1, f1, g1, h1, i1, j1, k1, l1, m1, n1, o1, p1 := fun()
 	let a2, b2, c2, d2, e2, f2, g2, h2, i2, j2, k2, l2, m2, n2, o2, p2 := fun()

test/cmdlineTests/yul_stack_opt/output

@@ -5,11 +5,11 @@ Pretty printed source:
 object "object" {
     code {
         {
-            let a1, b1, c1, d1, e1, f1, g1, h1, i1, j1, k1, l1, m1, n1, o1, p1 := fun()
+            let a3, b3, c3, d3, e3, f3, g3, h3, i3, j3, k3, l3, m3, o3, p3 := fun()
-            let a2, b2, c2, d2, e2, f2, g2, h2, i2, j2, k2, l2, m2, n2, o2, p2 := fun()
+            let a3_1, b3_1, c3_1, d3_1, e3_1, f3_1, g3_1, h3_1, i3_1, j3_1, k3_1, l3_1, m3_1, o3_1, p3_1 := fun()
-            sstore(a1, a2)
+            sstore(a3, a3_1)
         }
-        function fun() -> a3, b3, c3, d3, e3, f3, g3, h3, i3, j3, k3, l3, m3, n3, o3, p3
+        function fun() -> a3, b3, c3, d3, e3, f3, g3, h3, i3, j3, k3, l3, m3, o3, p3
         {
             let _1 := 1
             sstore(_1, _1)
@@ -25,21 +25,35 @@ object "object" {
             sstore(11, _1)
             sstore(12, _1)
             sstore(13, _1)
+            a3 := _1
+            b3 := _1
+            c3 := _1
+            d3 := _1
+            e3 := _1
+            f3 := _1
+            g3 := _1
+            h3 := _1
+            i3 := _1
+            j3 := _1
+            k3 := _1
+            l3 := _1
+            m3 := _1
+            o3 := _1
+            p3 := _1
         }
     }
 }
 
 
 Binary representation:
-60056032565b505050505050505050505050505050601a6032565b5050505050505050505050505050508082555050609b565b60006000600060006000600060006000600060006000600060006000600060006001808155806002558060035580600455806005558060065580600755806008558060095580600a5580600b5580600c5580600d55505b909192939495969798999a9b9c9d9e9f565b
+60056030565b505050505050505050505050505060196030565b5050505050505050505050505050808255505060c3565b6000600060006000600060006000600060006000600060006000600060006001808155806002558060035580600455806005558060065580600755806008558060095580600a5580600b5580600c5580600d55809f50809e50809d50809c50809b50809a50809950809850809750809650809550809450809350809250809150505b909192939495969798999a9b9c9d9e565b
 
 Text representation:
-    /* "yul_stack_opt/input.sol":495:500   */
+    /* "yul_stack_opt/input.sol":3:573   */
   tag_1
   tag_2
   jump	// in
 tag_1:
-    /* "yul_stack_opt/input.sol":425:500   */
   pop
   pop
   pop
@@ -54,13 +68,10 @@ tag_1:
   pop
   pop
   pop
-  pop
-    /* "yul_stack_opt/input.sol":572:577   */
   tag_3
   tag_2
   jump	// in
 tag_3:
-    /* "yul_stack_opt/input.sol":502:577   */
   pop
   pop
   pop
@@ -75,16 +86,15 @@ tag_3:
   pop
   pop
   pop
-  pop
+    /* "yul_stack_opt/input.sol":740:742   */
-    /* "yul_stack_opt/input.sol":590:592   */
   dup1
-    /* "yul_stack_opt/input.sol":586:588   */
+    /* "yul_stack_opt/input.sol":736:738   */
   dup3
-    /* "yul_stack_opt/input.sol":579:593   */
+    /* "yul_stack_opt/input.sol":729:743   */
   sstore
   pop
   pop
-    /* "yul_stack_opt/input.sol":3:423   */
+    /* "yul_stack_opt/input.sol":3:573   */
   jump(tag_4)
 tag_2:
   0x00
@@ -101,7 +111,6 @@ tag_2:
   0x00
   0x00
   0x00
-  0x00
   0x00
     /* "yul_stack_opt/input.sol":98:99   */
   0x01
@@ -181,8 +190,83 @@ tag_2:
   0x0d
     /* "yul_stack_opt/input.sol":399:420   */
   sstore
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":423:430   */
+  swap16
   pop
-    /* "yul_stack_opt/input.sol":85:423   */
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":433:440   */
+  swap15
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":443:450   */
+  swap14
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":453:460   */
+  swap13
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":463:470   */
+  swap12
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":473:480   */
+  swap11
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":483:490   */
+  swap10
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":493:500   */
+  swap9
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":503:510   */
+  swap8
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":513:520   */
+  swap7
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":523:530   */
+  swap6
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":533:540   */
+  swap5
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":543:550   */
+  swap4
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":553:560   */
+  swap3
+  pop
+    /* "yul_stack_opt/input.sol":98:99   */
+  dup1
+    /* "yul_stack_opt/input.sol":563:570   */
+  swap2
+  pop
+  pop
+    /* "yul_stack_opt/input.sol":85:573   */
 tag_5:
   swap1
   swap2
@@ -199,6 +283,5 @@ tag_5:
   swap13
   swap14
   swap15
-  swap16
   jump	// out
 tag_4:

test/libsolidity/StandardCompiler.cpp

@@ -29,6 +29,7 @@
 #include <libsolutil/CommonData.h>
 #include <test/Metadata.h>
 
+#include <algorithm>
 #include <set>
 
 using namespace std;
@@ -1235,9 +1236,16 @@ BOOST_AUTO_TEST_CASE(use_stack_optimization)
 	BOOST_REQUIRE(contract["evm"]["bytecode"]["object"].isString());
 	BOOST_CHECK(contract["evm"]["bytecode"]["object"].asString().length() > 20);
 
-	// Now disable stack optimizations
+	// Now disable stack optimizations and UnusedFunctionParameterPruner (p)
 	// results in "stack too deep"
+	string optimiserSteps = OptimiserSettings::DefaultYulOptimiserSteps;
+	optimiserSteps.erase(
+		remove_if(optimiserSteps.begin(), optimiserSteps.end(), [](char ch) { return ch == 'p'; }),
+		optimiserSteps.end()
+	);
 	parsedInput["settings"]["optimizer"]["details"]["yulDetails"]["stackAllocation"] = false;
+	parsedInput["settings"]["optimizer"]["details"]["yulDetails"]["optimizerSteps"] = optimiserSteps;
+
 	result = compiler.compile(parsedInput);
 	BOOST_REQUIRE(result["errors"].isArray());
 	BOOST_CHECK(result["errors"][0]["severity"] == "error");

test/libsolidity/gasTests/abiv2_optimised.sol

@@ -17,9 +17,9 @@ contract C {
 // optimize-yul: true
 // ----
 // creation:
-//   codeDepositCost: 616600
+//   codeDepositCost: 614600
 //   executionCost: 651
-//   totalCost: 617251
+//   totalCost: 615251
 // external:
 //   a(): 1029
 //   b(uint256): 2084

test/libyul/YulOptimizerTest.cpp

@@ -49,6 +49,7 @@
 #include <libyul/optimiser/NameDisplacer.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
+#include <libyul/optimiser/UnusedFunctionParameterPruner.h>
 #include <libyul/optimiser/UnusedPruner.h>
 #include <libyul/optimiser/ExpressionJoiner.h>
 #include <libyul/optimiser/OptimiserStep.h>
@@ -241,6 +242,13 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 		ExpressionJoiner::run(*m_context, *m_object->code);
 		ExpressionJoiner::run(*m_context, *m_object->code);
 	}
+	else if (m_optimizerStep == "unusedFunctionParameterPruner")
+	{
+		disambiguate();
+		FunctionHoister::run(*m_context, *m_object->code);
+		LiteralRematerialiser::run(*m_context, *m_object->code);
+		UnusedFunctionParameterPruner::run(*m_context, *m_object->code);
+	}
 	else if (m_optimizerStep == "unusedPruner")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/fullSuite/stack_compressor_msize.yul

@@ -49,7 +49,7 @@
 //         sstore(not(gcd(10, 15)), 1)
 //         sstore(0, 0)
 //         sstore(2, 1)
-//         pop(foo_singlereturn_1(calldataload(0), calldataload(3)))
+//         extcodecopy(1, msize(), 1, 1)
 //         sstore(0, 0)
 //         sstore(3, 1)
 //     }
@@ -59,6 +59,4 @@
 //         case 0 { out := _a }
 //         default { out := gcd(_b, mod(_a, _b)) }
 //     }
-//     function foo_singlereturn_1(in, in_1) -> out
-//     { extcodecopy(1, msize(), 1, 1) }
 // }

test/libyul/yulOptimizerTests/fullSuite/unusedFunctionParameterPruner.yul

@@ -0,0 +1,31 @@
+{
+    let x, y := foo(sload(0),sload(32))
+    sstore(0, x)
+    sstore(0, y)
+    x, y := foo(sload(32), sload(8))
+
+    function foo(a, b) -> out1, out2
+    {
+        out1 := mload(32)
+        out1 := sload(out1)
+        out2 := add(out1, 1)
+        extcodecopy(out1, out2, 1, b)
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         let out1, out2 := foo(sload(32))
+//         sstore(0, out1)
+//         sstore(0, out2)
+//         let out1_1, out2_1 := foo(sload(8))
+//     }
+//     function foo(b) -> out1, out2
+//     {
+//         out1 := sload(mload(32))
+//         out2 := add(out1, 1)
+//         extcodecopy(out1, out2, 1, b)
+//     }
+// }

test/libyul/yulOptimizerTests/fullSuite/unusedFunctionParameterPruner_loop.yul

@@ -0,0 +1,33 @@
+{
+    sstore(f(1), 1)
+    sstore(f(2), 1)
+    sstore(f(3), 1)
+    function f(a) -> x {
+        for {let b := 10} iszero(b) { b := sub(b, 1) }
+        {
+            a := calldataload(0)
+            mstore(a, x)
+        }
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         f()
+//         sstore(0, 1)
+//         f()
+//         sstore(0, 1)
+//         f()
+//         sstore(0, 1)
+//     }
+//     function f()
+//     {
+//         let b := 10
+//         let _1 := 0
+//         let a := calldataload(_1)
+//         for { } iszero(b) { b := add(b, not(0)) }
+//         { mstore(a, _1) }
+//     }
+// }

test/libyul/yulOptimizerTests/fullSuite/unusedFunctionParameterPruner_recursion.yul

@@ -0,0 +1,29 @@
+{
+    let j, k, l := f(1, 2, 3)
+    sstore(0, j)
+    sstore(1, k)
+    sstore(1, l)
+    function f(a, b, c) -> x, y, z
+    {
+        x, y, z := f(1, 2, 3)
+        x := add(x, 1)
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         let x, y, z := f()
+//         sstore(0, x)
+//         sstore(1, y)
+//         sstore(1, z)
+//     }
+//     function f() -> x, y, z
+//     {
+//         let x_1, y_1, z_1 := f()
+//         y := y_1
+//         z := z_1
+//         x := add(x_1, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/fullSuite/unusedFunctionParameterPruner_return.yul

@@ -0,0 +1,34 @@
+{
+    let x, y, z := foo(sload(0),sload(32))
+    sstore(0, x)
+    sstore(0, y)
+    sstore(0, z)
+    x, y, z := foo(sload(32), sload(8))
+
+    // out3 is unassigned.
+    function foo(a, b) -> out1, out2, out3
+    {
+        out1 := mload(32)
+        out1 := sload(out1)
+        out2 := add(out1, 1)
+        extcodecopy(out1, out1, 1, b)
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         let out1, out2 := foo(sload(32))
+//         sstore(0, out1)
+//         sstore(0, out2)
+//         sstore(0, 0)
+//         let out1_1, out2_1 := foo(sload(8))
+//     }
+//     function foo(b) -> out1, out2
+//     {
+//         out1 := sload(mload(32))
+//         out2 := add(out1, 1)
+//         extcodecopy(out1, out1, 1, b)
+//     }
+// }

test/libyul/yulOptimizerTests/fullSuite/unusedFunctionParameterPruner_simple.yul

@@ -0,0 +1,36 @@
+{
+    sstore(f(1), 1)
+    sstore(f(2), 1)
+    sstore(f(3), 1)
+    function f(a) -> x {
+        // The usage of a is redundant
+        a := calldataload(0)
+        mstore(a, x)
+        // to prevent getting fully inlined
+        sstore(1, 1)
+        sstore(2, 2)
+        sstore(3, 3)
+        sstore(3, 3)
+    }
+}
+// ----
+// step: fullSuite
+//
+// {
+//     {
+//         f()
+//         sstore(0, 1)
+//         f()
+//         sstore(0, 1)
+//         f()
+//         sstore(0, 1)
+//     }
+//     function f()
+//     {
+//         mstore(calldataload(0), 0)
+//         sstore(1, 1)
+//         sstore(2, 2)
+//         sstore(3, 3)
+//         sstore(3, 3)
+//     }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/LiteralRematerialiser.yul

@@ -0,0 +1,27 @@
+{
+    let a := f(mload(1))
+    let b := f(a)
+    sstore(a, b)
+    function f(x) -> y
+    {
+        // Test if LiteralRematerializer can convert `y` to `0` and therefore allowing us to
+        // rewrite the function f
+        if iszero(x) { revert(y, y)}
+        if iszero(add(x, 1)) { revert(y, y)}
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     let a := f_1(mload(1))
+//     let b := f_1(a)
+//     sstore(a, b)
+//     function f(x)
+//     {
+//         if iszero(x) { revert(0, 0) }
+//         if iszero(add(x, 1)) { revert(0, 0) }
+//     }
+//     function f_1(x_2) -> y_3
+//     { f(x_2) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/multiple_param.yul

@@ -0,0 +1,24 @@
+{
+    let d, e, i := f(1, 2, 3)
+    sstore(d, 0)
+    // b and x are unused
+    function f(a, b, c) -> x, y, z
+    {
+       y := mload(a)
+       z := mload(c)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     let d, e, i := f_1(1, 2, 3)
+//     sstore(d, 0)
+//     function f(a, c) -> y, z
+//     {
+//         y := mload(a)
+//         z := mload(c)
+//     }
+//     function f_1(a_2, b_3, c_4) -> x_5, y_6, z_7
+//     { y_6, z_7 := f(a_2, c_4) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/multiple_return.yul

@@ -0,0 +1,24 @@
+{
+    let a, b, c := f(sload(0))
+    sstore(a, 0)
+    // d is unused, x is unassigned
+    function f(d) -> x, y, z
+    {
+       y := mload(1)
+       z := mload(2)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     let a, b, c := f_1(sload(0))
+//     sstore(a, 0)
+//     function f() -> y, z
+//     {
+//         y := mload(1)
+//         z := mload(2)
+//     }
+//     function f_1(d_2) -> x_3, y_4, z_5
+//     { y_4, z_5 := f() }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/nested_function.yul

@@ -0,0 +1,56 @@
+// Test case to see if the step applies for nested functions. The function `j` has an unused argument.
+{
+    sstore(f(1), 0)
+    sstore(h(1), 0)
+
+    function f(a) -> x
+    {
+        x := g(1)
+        x := add(x, 1)
+        function g(b) -> y
+        {
+            b := add(b, 1)
+            y := mload(b)
+        }
+    }
+
+    function h(c) -> u
+    {
+        u := j(c)
+        // d is unused
+        function j(d) -> w
+        {
+            w := 13
+            w := add(w, 1)
+        }
+    }
+
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     sstore(f_1(1), 0)
+//     sstore(h(1), 0)
+//     function g(b) -> y
+//     {
+//         b := add(b, 1)
+//         y := mload(b)
+//     }
+//     function f() -> x
+//     {
+//         x := g(1)
+//         x := add(x, 1)
+//     }
+//     function f_1(a_3) -> x_4
+//     { x_4 := f() }
+//     function j() -> w
+//     {
+//         w := 13
+//         w := add(13, 1)
+//     }
+//     function j_2(d_5) -> w_6
+//     { w_6 := j() }
+//     function h(c) -> u
+//     { u := j_2(c) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/nested_function_name_collision.yul

@@ -0,0 +1,52 @@
+// Test case where the name `g` occurs at two different places. Test to see if name-collision can
+// cause issues.
+{
+    sstore(h(1), 0)
+    sstore(f(1), 0)
+
+    function f(c) -> u
+    {
+        u := g(c)
+        function g(d) -> w
+        {
+            w := 13
+            sstore(0, w)
+        }
+    }
+
+    function h(c) -> u
+    {
+        u := g(c)
+        function g(d) -> w
+        {
+            w := 13
+            sstore(0, w)
+        }
+    }
+
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     sstore(h(1), 0)
+//     sstore(f(1), 0)
+//     function g() -> w
+//     {
+//         w := 13
+//         sstore(0, 13)
+//     }
+//     function g_1(d_3) -> w_4
+//     { w_4 := g() }
+//     function f(c) -> u
+//     { u := g_1(c) }
+//     function g_3() -> w_5
+//     {
+//         w_5 := 13
+//         sstore(0, 13)
+//     }
+//     function g_3_2(d_4_5) -> w_5_6
+//     { w_5_6 := g_3() }
+//     function h(c_1) -> u_2
+//     { u_2 := g_3_2(c_1) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/no_return.yul

@@ -0,0 +1,21 @@
+{
+    f(1, 2)
+    function f(a, b)
+    {
+        sstore(a, 0)
+        a := add(a, 1)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     f_1(1, 2)
+//     function f(a)
+//     {
+//         sstore(a, 0)
+//         a := add(a, 1)
+//     }
+//     function f_1(a_2, b_3)
+//     { f(a_2) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/no_unused.yul

@@ -0,0 +1,16 @@
+// A test where all parameters are used
+{
+    sstore(f(1), 0)
+    function f(a) -> x { x := a }
+    function g(b) -> y { y := g(b) }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     sstore(f(1), 0)
+//     function f(a) -> x
+//     { x := a }
+//     function g(b) -> y
+//     { y := g(b) }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/recursion.yul

@@ -0,0 +1,21 @@
+{
+    let a1, b1, c1 := f(1, 2, 3)
+    function f(a, b, c) -> x, y, z
+    {
+        x, y, z := f(1, 2, 3)
+        x := add(x, 1)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     let a1, b1, c1 := f_1(1, 2, 3)
+//     function f() -> x, y, z
+//     {
+//         x, y, z := f_1(1, 2, 3)
+//         x := add(x, 1)
+//     }
+//     function f_1(a_2, b_3, c_4) -> x_5, y_6, z_7
+//     { x_5, y_6, z_7 := f() }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/simple.yul

@@ -0,0 +1,21 @@
+{
+    sstore(f(1), 0)
+    function f(x) -> y
+    {
+        let w := mload(1)
+        y := mload(w)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     sstore(f_1(1), 0)
+//     function f() -> y
+//     {
+//         let w := mload(1)
+//         y := mload(w)
+//     }
+//     function f_1(x_2) -> y_3
+//     { y_3 := f() }
+// }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/smoke.yul

@@ -0,0 +1,5 @@
+{}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// { }

test/libyul/yulOptimizerTests/unusedFunctionParameterPruner/too_many_arguments.yul

@@ -0,0 +1,23 @@
+{
+    let a, b := f(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
+    sstore(a, b)
+    function f(x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15, x16, x17, x18) -> y, z
+    {
+       y := mload(x3)
+       z := mload(x7)
+    }
+}
+// ----
+// step: unusedFunctionParameterPruner
+//
+// {
+//     let a, b := f_1(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
+//     sstore(a, b)
+//     function f(x3, x7) -> y, z
+//     {
+//         y := mload(x3)
+//         z := mload(x7)
+//     }
+//     function f_1(x1_2, x2_3, x3_4, x4_5, x5_6, x6_7, x7_8, x8_9, x9_10, x10_11, x11_12, x12_13, x13_14, x14_15, x15_16, x16_17, x17_18, x18_19) -> y_20, z_21
+//     { y_20, z_21 := f(x3_4, x7_8) }
+// }

test/yulPhaser/Chromosome.cpp

@@ -130,7 +130,7 @@ BOOST_AUTO_TEST_CASE(output_operator_should_create_concise_and_unambiguous_strin
 
 	BOOST_TEST(chromosome.length() == allSteps.size());
 	BOOST_TEST(chromosome.optimisationSteps() == allSteps);
-	BOOST_TEST(toString(chromosome) == "flcCUnDvejsxIOoighTLMrmVatud");
+	BOOST_TEST(toString(chromosome) == "flcCUnDvejsxIOoighTLMrmVatpud");
 }
 
 BOOST_AUTO_TEST_CASE(randomOptimisationStep_should_return_each_step_with_same_probability)

test/yulPhaser/Mutations.cpp

@@ -103,10 +103,10 @@ BOOST_AUTO_TEST_CASE(geneAddition_should_iterate_over_gene_positions_and_insert_
 	SimulationRNG::reset(1);
 	//                                                                 f  c  C  U  n  D  v  e  j  s
 	BOOST_TEST(mutation01(chromosome) == Chromosome(stripWhitespace("  f  c  C  UC n  D  v  e  jx s")));  //  20% more
-	BOOST_TEST(mutation05(chromosome) == Chromosome(stripWhitespace("j f  cu C  U  ne D  v  eI j  sf"))); //  50% more
+	BOOST_TEST(mutation05(chromosome) == Chromosome(stripWhitespace("s f  cu C  U  nj D  v  eI j  sf"))); //  50% more
 	SimulationRNG::reset(2);
 	BOOST_TEST(mutation01(chromosome) == Chromosome(stripWhitespace("  f  cu C  U  n  D  v  e  j  s")));  //  10% more
-	BOOST_TEST(mutation05(chromosome) == Chromosome(stripWhitespace("L f  ce Cv U  n  D  v  e  jO s")));  //  40% more
+	BOOST_TEST(mutation05(chromosome) == Chromosome(stripWhitespace("M f  ce Cv U  n  D  v  e  jo s")));  //  40% more
 }
 
 BOOST_AUTO_TEST_CASE(geneAddition_should_be_able_to_insert_before_first_position)