RTL type checking and '0' format codes

[Zack Weinberg]

Jeffrey A Law wrote:
>   In message < 199908162310.QAA09148@zack.bitmover.com >you write:
>   > 
>   > I have been looking into implementing type checking for RTL, much like
>   > the type checking for trees we already have.
[...]
>   > Most '0' slots are always addressed with a specific type, but the
>   > information on their type isn't in the format.  LABEL_NUSES,
>   > JUMP_LABEL, LABEL_REFS, LABEL_NEXTREF, and CONTAINING_INSN are like
>   > this.  We would like to type check them.
> I'd punt initially and get the basic checking code installed.  Then return
> to this issue.

Agree, and I'm actually testing a patch that does this even as we
speak.  It has knock-on effects all over the code and my patch backlog
is getting quite large, so I won't be able to submit it for awhile.

zw