1 files changed, 114 insertions, 0 deletions
diff --git a/libyul/optimiser/SSAReverser.cpp b/libyul/optimiser/SSAReverser.cpp
new file mode 100644
index 00000000..6548ebb5
--- /dev/null
+++ b/libyul/optimiser/SSAReverser.cpp
@@ -0,0 +1,114 @@
+/*
+	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/SSAReverser.h>
+#include <libyul/optimiser/Metrics.h>
+#include <libyul/AsmData.h>
+#include <libdevcore/CommonData.h>
+
+using namespace std;
+using namespace dev;
+using namespace yul;
+
+void SSAReverser::run(Block& _block)
+{
+	AssignmentCounter assignmentCounter;
+	assignmentCounter(_block);
+	SSAReverser{assignmentCounter}(_block);
+}
+
+void SSAReverser::operator()(Block& _block)
+{
+	walkVector(_block.statements);
+	iterateReplacingWindow<2>(
+		_block.statements,
+		[&](Statement& _stmt1, Statement& _stmt2) -> boost::optional<vector<Statement>>
+		{
+			auto* varDecl = boost::get<VariableDeclaration>(&_stmt1);
+
+			if (!varDecl || varDecl->variables.size() != 1 || !varDecl->value)
+				return {};
+
+			// Replaces
+			//   let a_1 := E
+			//   a := a_1
+			// with
+			//   a := E
+			//   let a_1 := a
+			if (auto* assignment = boost::get<Assignment>(&_stmt2))
+			{
+				auto* identifier = boost::get<Identifier>(assignment->value.get());
+				if (
+					assignment->variableNames.size() == 1 &&
+					identifier &&
+					identifier->name == varDecl->variables.front().name
+				)
+				{
+					vector<Statement> result;
+					result.emplace_back(Assignment{
+						std::move(assignment->location),
+						assignment->variableNames,
+						std::move(varDecl->value)
+					});
+					result.emplace_back(VariableDeclaration{
+						std::move(varDecl->location),
+						std::move(varDecl->variables),
+						std::make_unique<Expression>(std::move(assignment->variableNames.front()))
+					});
+					return { std::move(result) };
+				}
+			}
+			// Replaces
+			//   let a_1 := E
+			//   let a := a_1
+			// with
+			//   let a := E
+			//   let a_1 := a
+			else if (auto* varDecl2 = boost::get<VariableDeclaration>(&_stmt2))
+			{
+				auto* identifier = boost::get<Identifier>(varDecl2->value.get());
+				if (
+					varDecl2->variables.size() == 1 &&
+					identifier &&
+					identifier->name == varDecl->variables.front().name && (
+						m_assignmentCounter.assignmentCount(varDecl2->variables.front().name) >
+						m_assignmentCounter.assignmentCount(varDecl->variables.front().name)
+				   )
+				)
+				{
+					vector<Statement> result;
+					auto varIdentifier2 = std::make_unique<Expression>(Identifier{
+						varDecl2->variables.front().location,
+						varDecl2->variables.front().name
+					});
+					result.emplace_back(VariableDeclaration{
+						std::move(varDecl2->location),
+						std::move(varDecl2->variables),
+						std::move(varDecl->value)
+					});
+					result.emplace_back(VariableDeclaration{
+						std::move(varDecl->location),
+						std::move(varDecl->variables),
+						std::move(varIdentifier2)
+					});
+					return { std::move(result) };
+				}
+			}
+
+			return {};
+		}
+	);
+}