[decomp] Split condition and body of until after building expressions (#768)

* improve until decomp

* fix tests

decompiler/IR2/FormExpressionAnalysis.cpp

@@ -2922,16 +2922,51 @@ void DerefElement::inline_nested() {
 ///////////////////
 
 void UntilElement::push_to_stack(const Env& env, FormPool& pool, FormStack& stack) {
+  // in asm:
+  // LTOP:
+  //  body
+  //  condition
+  //  jump to top
+  // so we can end up getting the body/condition wrong.
+  // the way the CfgPass works means that we put too much in condition.
+  // we can safely move stuff from the top of condition to the bottom of body.
+
   mark_popped();
-  for (auto form : {condition, body}) {
-    FormStack temp_stack(false);
-    for (auto& entry : form->elts()) {
-      entry->push_to_stack(env, pool, temp_stack);
+
+  std::vector<FormElement*> condition_to_body;
+  {
+    FormStack condition_temp_stack(false);
+    for (auto& entry : condition->elts()) {
+      entry->push_to_stack(env, pool, condition_temp_stack);
     }
-    auto new_entries = temp_stack.rewrite(pool, env);
-    form->clear();
+    condition_to_body = condition_temp_stack.rewrite(pool, env);
+    condition->clear();
+    assert(!condition_to_body.empty());
+    condition->push_back(condition_to_body.back());
+    condition_to_body.pop_back();
+  }
+
+  {
+    FormStack body_temp_stack(false);
+    for (auto& entry : body->elts()) {
+      entry->push_to_stack(env, pool, body_temp_stack);
+    }
+    auto new_entries = body_temp_stack.rewrite(pool, env);
+    body->clear();
+
     for (auto e : new_entries) {
-      form->push_back(e);
+      if (!dynamic_cast<EmptyElement*>(e)) {
+        body->push_back(e);
+      }
+    }
+    for (auto e : condition_to_body) {
+      if (!dynamic_cast<EmptyElement*>(e)) {
+        body->push_back(e);
+      }
+    }
+
+    if (body->size() == 0) {
+      body->push_back(pool.alloc_element<EmptyElement>());
     }
   }