new do-count rtl

[Doug Evans]

Doug Evans wrote:
> Hi.
>
> What do folks think of adding a new rtl for iterating a specified 
> number of times.
>
> Something like
>
> (do-count nr-times iter-var expr1 [expr2 ...])
>
> For now the result would always be void, and iter-var would always 
> have mode INT.
> The set of expressions is performed nr-times times and iter-var has 
> values 0 ... nr-times - 1.
>
> ?
>

Checked in.

2009-08-27  Doug Evans  <dje@sebabeach.org>

        Add do-count rtl function.
        * rtl-c.scm (s-do-count): New function.
        (do-count): New rtl handler.
        * rtl-traverse.scm (-rtx-traverse-iteration): New function.
        (-rtx-make-traverser-table): Add ITERATION.
        * rtl.scm (rtx-env-make-iteration-locals): New function.
        * rtx-funcs.scm (do-count): New rtl function.
        * cpu/play.cpu: Add do-count-test insn.
        * doc/rtl.texi: Add docs on do-count.