Re: [RFC] completely peel loops unconditionally

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> This proof of concept patch enables complete loop peeling unconditionally
> (if -floop-optimize is specified, i.e. at -O1).  This is most definitely
> always a win (but see below) and there is no way currently to only enable
> complete peeling without general peeling.

I believe you would at least need to check whether the loop you unroll
is small enough.  But I suggest wait till we merge the lno branch stuff,
since complete unrolling of small loops would more profitably be done
there (in fact it needs just changing a few lines of code there to
achieve it).  Provided everything goes well, we should have this in 3.5.

Zdenek

> Thanks,
> Richard.
> 
> 2004Jun16  Richard Guenther <richard.guenther@uni-tuebingen.de>
> 
> 	* passes.c (rest_of_handle_loop2): call peel_loops_completely.
> 	cfgloop.h: export it.
> 	loop-unroll.c: likewise.
> 	(unroll_and_peel_loops): don't peel_loops_completely again.
> 
> Index: passes.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/passes.c,v
> retrieving revision 2.19
> diff -u -u -r2.19 passes.c
> --- passes.c	16 Jun 2004 07:25:52 -0000	2.19
> +++ passes.c	16 Jun 2004 10:56:15 -0000
> @@ -1400,6 +1400,9 @@
>        if (flag_unswitch_loops)
>  	unswitch_loops (loops);
> 
> +      /* Peeling small loops completely is always a win.  */
> +      peel_loops_completely (loops, 0);
> +
>        if (flag_peel_loops || flag_unroll_loops)
>  	unroll_and_peel_loops (loops,
>  			       (flag_peel_loops ? UAP_PEEL : 0) |
> Index: cfgloop.h
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cfgloop.h,v
> retrieving revision 1.19
> diff -u -u -r1.19 cfgloop.h
> --- cfgloop.h	3 Jun 2004 15:01:08 -0000	1.19
> +++ cfgloop.h	16 Jun 2004 10:56:16 -0000
> @@ -426,6 +426,7 @@
>  };
> 
>  extern void unroll_and_peel_loops (struct loops *, int);
> +extern void peel_loops_completely (struct loops *, int);
>  extern void doloop_optimize_loops (struct loops *);
> 
>  #endif /* GCC_CFGLOOP_H */
> Index: loop-unroll.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/loop-unroll.c,v
> retrieving revision 1.16
> diff -u -u -r1.16 loop-unroll.c
> --- loop-unroll.c	24 Feb 2004 23:39:55 -0000	1.16
> +++ loop-unroll.c	16 Jun 2004 10:56:16 -0000
> @@ -67,7 +67,7 @@
>     */
> 
>  static void decide_unrolling_and_peeling (struct loops *, int);
> -static void peel_loops_completely (struct loops *, int);
> +void peel_loops_completely (struct loops *, int);
>  static void decide_peel_simple (struct loop *, int);
>  static void decide_peel_once_rolling (struct loop *, int);
>  static void decide_peel_completely (struct loop *, int);
> @@ -87,9 +87,9 @@
>    struct loop *loop, *next;
>    bool check;
> 
> -  /* First perform complete loop peeling (it is almost surely a win,
> +  /* Complete loop peeling was performed unconditionally in
> +     rest_of_handle_loop2. (it is almost surely a win,
>       and affects parameters for further decision a lot).  */
> -  peel_loops_completely (loops, flags);
> 
>    /* Now decide rest of unrolling and peeling.  */
>    decide_unrolling_and_peeling (loops, flags);