Ping: RFA: Improve doloop_begin support

[Zdenek Dvorak]

> Quoting Zdenek Dvorak <rakdver@iuuk.mff.cuni.cz>:
> 
> >no -- you should also test that latch contains no active insns.
> >I.e., factorize
> >out whatever forwarder_block_p does except for the test
> >"(dest->loop_father->header == dest)" test,
> 
> Like this?
> 
>         * basic-block.h (forwarder_block_p_1): Declare.
>         * cfgrtl.c (orwarder_block_p_1): New function, factored out of ...
>         (orwarder_block_p): ... here.

yes (except maybe giving it some more descriptive name than forwarder_block_p_1,
say "contains_no_active_insn_p" or something),

Zdenek