The problem isn't just faking a stack with a fast buffer, it's figuring out where the sources are, or rather, will be, with pipelined execution, or worse yet, d

The problem isn't just faking a stack with a fast buffer, it's figuring out where the sources are, or rather, will be, with pipelined execution, or worse yet, decoding multiple instructions at once. You also want to have multiple instructions writing a given architectural resource live at once. That's tough if top-of-stack is a buffer location.