on non-rtl function info

[Joern Rennecke]

>   > On the subject of the first, I'm not sure what is the best thing to do.
>   > Something that came to mind was having documented global stores of such
>   > information.  Each passes would record when something it does kills the
>   > information, and each pass would begin with assertions that verify that
>   > the required info is still live, possibly regenerating it if not.
> That may be OK short term, but long term we should be thinking about using
> data structures that we can update on the fly or incrementally at the end
> of a pass.

Hmmm, we have this with REG_DEAD notes in reload - if
PRESERVE_DEATH_INFO_REGNO_P is defined - and are moving away from it...