Re: [CFG] Unswitching cleanup

[Jan Hubicka <jh at suse dot cz>]

> Hello.
> 
> This patch cleans up the code concerning loop unswitching a lot, removing most
> of the dark magic.  It also allows us to really remove the loop when we peel it
> completely (till now we were just leaving it in place, hoping that some
> following optimization pass will get rid of it).

Thanks.  I will take a look at it shortly. One thing I was thinking about
is that we may make the unswitching independent on the midrtl just
by using canonicalize_comparison on the condition we get from condtiional
and re-emiting the jump again based on the comparison.  I will take a look
how dificult it is to integrate into current design.

> *************** void verify_loop_structure (loops, flags
> *** 1140,1145 ****
> --- 1201,1209 ----
>     for (i = 1; i < loops->num; i++)
>       {
>         loop = loops->parray[i];
> +       if (!loop)
> + 	continue;
> + 

This looks fine. I am affrait there is a lot more places we will have
to care NULL pointers tought.

> ! 
> !   /* Find border hexes.  */
What do you mean by the border hexes?

> *************** count_loop_iterations (desc, niter, rnit
> *** 418,427 ****
>     unsigned HOST_WIDE_INT abs_diff = 0;
>     enum rtx_code cond = desc->cond;
>   
>     if (desc->grow)
>       {
>         /* Bypass nonsential tests.  */
> !       if (cond == GE || cond == GT || cond == GEU || cond == GTU)
>   	return false;
>         if (rniter)
>   	{
> --- 432,449 ----
>     unsigned HOST_WIDE_INT abs_diff = 0;
>     enum rtx_code cond = desc->cond;
>   
> +   /* Ensure that we always handle the condition to stay inside loop.  */
> +   if (desc->neg)
> +     {
> +       cond = reverse_condition (cond);
> +       if (cond == UNKNOWN)
> + 	return false;
> +     }
> + 

Hmm, how can the UNKNOWNS get here?  They can happen only for floats
and we hsould rule them out earlier.  I guess I will just add the
test into simple_loop to verify that induction variable is integral.
> *************** count_loop_iterations (desc, niter, rnit
> *** 458,470 ****
>   		 << (GET_MODE_BITSIZE (GET_MODE (desc->var)) - 1)
>   		 << 1) - 1;
>         
> -   if (desc->neg)
> -     {
> -       cond = reverse_condition (cond);
> -       if (cond == UNKNOWN)
> - 	return false;
> -     }
> - 
Uhm, I see it is negated but later. Moving it earlier is definitly
good idea.


Thanks!
I will install your patch as it makes thinks just better and try
to make incremental patch over it.  I see it is touchy issue and
it would be nice to get it understandable. I am not sure if it
is possible tought :(

Honza