It should be possible to mark some of our runtime functions with argmemonly readonly as they receive their type arguments indirectly via an array of type arguments.
I tried this in https://github.com/apple/swift/pull/14310 but tests failed. I did not have time to investigate why.
I mentioned that if that following situation in some form or another this annotation is not legal:
However, we believe that this situation should? not arise. It might be worth investigating the failures.