RET as a last instruction could be safely ignored. Remove it to prevent crashes/warnings in case underlying driver doesn't implement arbitrary returns.
A better way would be to remove the RET after the whole shader is parsed which will handle a possible case when the last RET is followed by a comment.
This would fix crash in Lunatic Rave 2 which has ret at the end of one vertex shader. Apitrace of the game could be found at https://github.com/Joshua-Ashton/d9vk/issues/192