Require for loop init rewriter for SSA.

Co-authored-by: Harikrishnan Mulackal <webmail.hari@gmail.com>

libyul/optimiser/SSATransform.cpp

@@ -194,7 +194,7 @@ void IntroduceControlFlowSSA::operator()(FunctionDefinition& _function)
 
 void IntroduceControlFlowSSA::operator()(ForLoop& _for)
 {
-	(*this)(_for.pre);
+	yulAssert(_for.pre.statements.empty(), "For loop init rewriter not run.");
 
 	Assignments assignments;
 	assignments(_for.body);
@@ -357,11 +357,7 @@ void PropagateValues::operator()(Assignment& _assignment)
 
 void PropagateValues::operator()(ForLoop& _for)
 {
-	// This will clear the current value in case of a reassignment inside the
-	// init part, although the new variable would still be in scope inside the whole loop.
-	// This small inefficiency is fine if we move the pre part of all for loops out
-	// of the for loop.
-	(*this)(_for.pre);
+	yulAssert(_for.pre.statements.empty(), "For loop init rewriter not run.");
 
 	Assignments assignments;
 	assignments(_for.body);

libyul/optimiser/SSATransform.h

@@ -85,7 +85,7 @@ class NameDispenser;
  *
  * TODO Which transforms are required to keep this idempotent?
  *
- * Prerequisite: Disambiguator.
+ * Prerequisite: Disambiguator, ForLoopInitRewriter.
  */
 class SSATransform: public ASTModifier
 {