Yul: Implements empty-var-decl-propagation

test/libyul/YulOptimizerTest.cpp

@@ -22,6 +22,7 @@
 #include <test/Options.h>
 
 #include <libyul/optimiser/BlockFlattener.h>
+#include <libyul/optimiser/VarDeclPropagator.h>
 #include <libyul/optimiser/Disambiguator.h>
 #include <libyul/optimiser/CommonSubexpressionEliminator.h>
 #include <libyul/optimiser/NameCollector.h>
@@ -102,6 +103,11 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 		disambiguate();
 		BlockFlattener{}(*m_ast);
 	}
+	else if (m_optimizerStep == "varDeclPropagator")
+	{
+		disambiguate();
+		VarDeclPropagator{}(*m_ast);
+	}
 	else if (m_optimizerStep == "commonSubexpressionEliminator")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/varDeclPropagator/init_assignment_inside_if.yul

@@ -0,0 +1,17 @@
+{
+  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

@@ -0,0 +1,13 @@
+{
+  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

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

test/libyul/yulOptimizerTests/varDeclPropagator/rewrite_removes_unused_var.yul

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

test/libyul/yulOptimizerTests/varDeclPropagator/simple1.yul

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

test/libyul/yulOptimizerTests/varDeclPropagator/split_assign_splits_vardecl.yul

@@ -0,0 +1,11 @@
+{
+  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

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

test/libyul/yulOptimizerTests/varDeclPropagator/use_doesnt_rewrite.yul

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