[Decompiler] Flag uses of vf registers for values outside of functions (#263)

* clean up warning system

* add bad dependency warning

* add q and acc

decompiler/analysis/cfg_builder.cpp

@@ -165,6 +165,7 @@ void clean_up_return_final(const Function& f, ReturnElement* ir) {
   if (!dead) {
     lg::error("failed to recognize dead code after return, got {}",
               ir->dead_code->to_string(f.ir2.env));
+    throw std::runtime_error("failed to recognize dead code");
   }
   assert(dead);
   auto src = dynamic_cast<SimpleExpressionElement*>(dead->src()->try_as_single_element());