Re: [PATCH] Improve backwards threading

[Jeff Law <law at redhat dot com>]

On 08/05/2016 07:36 AM, Richard Biener wrote:
> @@ -560,6 +562,14 @@ fsm_find_control_statement_thread_paths
>           edge taken_edge = profitable_jump_thread_path (path, bbi, name,
> arg);
>           if (taken_edge)
>             {
> +             /* If the taken edge is a loop entry avoid mashing two
> +                loops into one with multiple latches by splitting
> +                the edge.  This only works if that block won't become
> +                a latch of this loop.  */
> +             if ((bb_loop_depth (taken_edge->src)
> +                  < bb_loop_depth (taken_edge->dest))
> +                 && ! single_succ_p (bbi))
> +               split_edge (taken_edge);
>               if (bb_loop_depth (taken_edge->src)
>                   >= bb_loop_depth (taken_edge->dest))
>                 convert_and_register_jump_thread_path (path, taken_edge);
>
> note you need the PR72772 fix to trigger all this.
I'm a little confused here.  In the case where the taken edge goes into 
a deeper loop nest you're splitting the edge -- to what end?  The 
backwards threader isn't going to register that jump thread.  So if this 
is fixing something, then we've got the fix in the wrong place.


FWIW, I the anonymous name fix ought to go in separately, it looks like 
the right thing to do independent of this stuff.

jeff