[Yul] Implements a pass to rewrite for-loop's pre block into the parent's Block.

test/libyul/YulOptimizerTest.cpp

@@ -31,6 +31,7 @@
 #include <libyul/optimiser/FunctionHoister.h>
 #include <libyul/optimiser/ExpressionInliner.h>
 #include <libyul/optimiser/FullInliner.h>
+#include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/MainFunction.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
@@ -108,6 +109,11 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 		disambiguate();
 		VarDeclPropagator{}(*m_ast);
 	}
+	else if (m_optimizerStep == "forLoopInitRewriter")
+	{
+		disambiguate();
+		ForLoopInitRewriter{}(*m_ast);
+	}
 	else if (m_optimizerStep == "commonSubexpressionEliminator")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/forLoopInitRewriter/complex_pre.yul

@@ -0,0 +1,23 @@
+{
+  let random := 42
+  for { let a := 1
+	    let b := 1 } iszero(eq(a, 10)) { a := add(a, b) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let random := 42
+//     let a := 1
+//     let b := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, b)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/forLoopInitRewriter/empty_pre.yul

@@ -0,0 +1,20 @@
+{
+  let a := 1
+  for {} iszero(eq(a, 10)) { a := add(a, 1) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let a := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, 1)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/forLoopInitRewriter/simple.yul

@@ -0,0 +1,21 @@
+{
+  let random := 42
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let random := 42
+//     let a := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, 1)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }