Fix variable decl scope issue in DeadCodeEliminator

FoorLoopInitRewriter needs to be run before DeadCodeEliminator.

libyul/optimiser/DeadCodeEliminator.h

@@ -38,6 +38,10 @@ namespace yul
  * Function definitions are retained as they might be called by earlier
  * code and thus are considered reachable.
  *
+ * Because variables declared in a for loop's init block have their scope extended to the loop body,
+ * we require ForLoopInitRewriter to run before this step.
+ *
+ * Prerequisite: ForLoopInitRewriter
  */
 class DeadCodeEliminator: public ASTModifier
 {

libyul/optimiser/Suite.cpp

@@ -71,11 +71,11 @@ void OptimiserSuite::run(
 	VarDeclInitializer{}(ast);
 	FunctionHoister{}(ast);
 	BlockFlattener{}(ast);
+	ForLoopInitRewriter{}(ast);
 	DeadCodeEliminator{}(ast);
 	FunctionGrouper{}(ast);
 	EquivalentFunctionCombiner::run(ast);
 	UnusedPruner::runUntilStabilised(*_dialect, ast, reservedIdentifiers);
-	ForLoopInitRewriter{}(ast);
 	BlockFlattener{}(ast);
 	StructuralSimplifier{*_dialect}(ast);
 	BlockFlattener{}(ast);

test/libyul/YulOptimizerTest.cpp

@@ -207,6 +207,7 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 	else if (m_optimizerStep == "deadCodeEliminator")
 	{
 		disambiguate();
+		ForLoopInitRewriter{}(*m_ast);
 		DeadCodeEliminator{}(*m_ast);
 	}
 	else if (m_optimizerStep == "ssaTransform")

test/libyul/yulOptimizerTests/deadCodeEliminator/conditional_break.yul

@@ -17,8 +17,8 @@
 // step: deadCodeEliminator
 // ----
 // {
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {

test/libyul/yulOptimizerTests/deadCodeEliminator/early_break.yul

@@ -18,8 +18,8 @@
 // step: deadCodeEliminator
 // ----
 // {
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {

test/libyul/yulOptimizerTests/deadCodeEliminator/early_continue.yul

@@ -18,8 +18,8 @@
 // step: deadCodeEliminator
 // ----
 // {
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {

test/libyul/yulOptimizerTests/deadCodeEliminator/for_loop_init_decl.yul

@@ -0,0 +1,12 @@
+{
+  for { stop() let i_0 := 0 } lt(i_0,2) { i_0 := add(i_0,1) }
+  {
+    let i_1 := i_0
+  }
+}
+// ====
+// step: deadCodeEliminator
+// ----
+// {
+//     stop()
+// }

test/libyul/yulOptimizerTests/deadCodeEliminator/normal_break.yul

@@ -16,8 +16,8 @@
 // step: deadCodeEliminator
 // ----
 // {
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {

test/libyul/yulOptimizerTests/deadCodeEliminator/normal_continue.yul

@@ -16,8 +16,8 @@
 // step: deadCodeEliminator
 // ----
 // {
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {

test/libyul/yulOptimizerTests/deadCodeEliminator/normal_stop.yul

@@ -20,8 +20,8 @@
 // ----
 // {
 //     let b := 20
+//     let a := 20
 //     for {
-//         let a := 20
 //     }
 //     lt(a, 40)
 //     {