Undo second SSA transformation and add more tests.

2 files changed, 74 insertions, 29 deletions

diff --git a/libyul/optimiser/SSAReverser.cpp b/libyul/optimiser/SSAReverser.cpp
index 313a677a..2cfa3d58 100644
--- a/libyul/optimiser/SSAReverser.cpp
+++ b/libyul/optimiser/SSAReverser.cpp
@@ -29,42 +29,74 @@ void SSAReverser::operator()(Block& _block)
 		_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
-
-			auto* varDecl = boost::get<VariableDeclaration>(&_stmt1);
-			auto* assignment = boost::get<Assignment>(&_stmt2);
-
-			if (!varDecl || !assignment)
-				return {};
-
-			auto* identifier = boost::get<Identifier>(assignment->value.get());
-
-			if (
-				varDecl->variables.size() == 1 &&
-				varDecl->value &&
-				assignment->variableNames.size() == 1 &&
-				identifier &&
-				identifier->name == varDecl->variables.front().name
-			)
+			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))
 			{
-				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) };
+				auto* identifier = boost::get<Identifier>(varDecl2->value.get());
+				if (
+					varDecl2->variables.size() == 1 &&
+					identifier &&
+					identifier->name == 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 {};
 		}
 	);
diff --git a/libyul/optimiser/SSAReverser.h b/libyul/optimiser/SSAReverser.h
index a4a11074..34b61647 100644
--- a/libyul/optimiser/SSAReverser.h
+++ b/libyul/optimiser/SSAReverser.h
@@ -33,11 +33,24 @@ namespace yul
  * 		let a_1 := E
  * 		a := a_1
  *
- * 	To undo this transformation, the SSAReverser changes this back to
+ * To undo this kind of transformation, the SSAReverser changes this back to
  *
  * 		a := E
  * 		let a_1 := a
  *
+ * Secondly, the SSA transform will rewrite
+ *
+ * 		let a := E
+ * to
+ *
+ * 		let a_1 := E
+ * 		let a := a_1
+ *
+ * To undo this kind of transformation, the SSAReverser changes this back to
+ *
+ * 		let a := E
+ * 		let a_1 := a
+ *
  * 	After that the CSE can replace references of a_1 by references to a,
  * 	after which the unused pruner can remove the declaration of a_1.
  *