Re: Re: [PATCH] LCM: Export 2 helpful functions as global for VSETVL PASS use in RISC-V backend

["juzhe.zhong@rivai.ai" <juzhe.zhong@rivai.ai>]

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Hi, Richi.

This patch is how I use LCM functions:
https://gcc.gnu.org/pipermail/gcc-patches/2023-August/627953.html 

>> they are just necessary
>> to compute pre_edge_lcm_avs which I see you already do.  

In Phase 4 I use pre_edge_lcm_av to PRE fo current VSETVL cfg information.
However, it's not enough since I need phase 3 fuse VSETVL information to get better codegen.

The is how I use the functions:

+      /* Compute global availability.  */
       compute_available (m_vector_manager->vector_comp,
 			 m_vector_manager->vector_kill,
 			 m_vector_manager->vector_avout,
 			 m_vector_manager->vector_avin);
-      changed_p |= cleanup_illegal_dirty_blocks ();
+      /* Compute global anticipatability.  */
+      compute_antinout_edge (m_vector_manager->vector_antic,
+			     m_vector_manager->vector_transp,
+			     m_vector_manager->vector_antin,
+			     m_vector_manager->vector_antout);
+      /* Compute earliestness.  */
+      compute_earliest (m_vector_manager->vector_edge_list,
+			m_vector_manager->vector_exprs.length (),
+			m_vector_manager->vector_antin,
+			m_vector_manager->vector_antout,
+			m_vector_manager->vector_avout,
+			m_vector_manager->vector_kill,
+			m_vector_manager->vector_earliest);
+      changed_p |= earliest_fusion ();
You can see I explicitly call 'compute_earliest' followed by 'earliest_fusion'I need the result from 'compute_earliest' to do the VSETVL fusion that's the information 'pre_edge_lcm_av' didn't give us.
>> Just to say
>> you are possibly going to blow up compile-time complexity of your
>> VSETVL dataflow problem?

No, I export 'compute_earliest' as global because 'pre_edge_lcm_av' didn't give us the 'earliest' result that I need.

Thanks.


juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2023-08-21 15:09
To: Juzhe-Zhong
CC: gcc-patches; jeffreyalaw
Subject: Re: [PATCH] LCM: Export 2 helpful functions as global for VSETVL PASS use in RISC-V backend
On Mon, 21 Aug 2023, Juzhe-Zhong wrote:
 
> This patch exports 'compute_antinout_edge' and 'compute_earliest' as global scope
> which is going to be used in VSETVL PASS of RISC-V backend.
> 
> The demand fusion is the fusion of VSETVL information to emit VSETVL which dominate and pre-config for most
> of the RVV instructions in order to elide redundant VSETVLs.
> 
> For exmaple:
> 
> for
>  for
>   for
>     if (cond}
>       VSETVL demand 1: SEW/LMUL = 16 and TU policy
>     else
>       VSETVL demand 2: SEW = 32
> 
> VSETVL pass should be able to fuse demand 1 and demand 2 into new demand: SEW = 32, LMUL = M2, TU policy.
> Then emit such VSETVL at the outmost of the for loop to get the most optimal codegen and run-time execution.
> 
> Currenty the VSETVL PASS Phase 3 (demand fusion) is really messy and un-reliable as well as un-maintainable.
> And, I recently read dragon book and morgan's book again, I found there "earliest" can allow us to do the
> demand fusion in a very reliable and optimal way.
> 
> So, this patch exports these 2 functions which are very helpful for VSETVL pass.
 
It would be nice to put these internal functions into a class or a
namespace given their non LCM name.  I don't see how you are going
to use these intermediate DF functions - they are just necessary
to compute pre_edge_lcm_avs which I see you already do.  Just to say
you are possibly going to blow up compile-time complexity of your
VSETVL dataflow problem?
 
> gcc/ChangeLog:
> 
> * lcm.cc (compute_antinout_edge): Export as global use.
> (compute_earliest): Ditto.
> (compute_rev_insert_delete): Ditto.
> * lcm.h (compute_antinout_edge): Ditto.
> (compute_earliest): Ditto.
> 
> ---
>  gcc/lcm.cc | 7 ++-----
>  gcc/lcm.h  | 3 +++
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/lcm.cc b/gcc/lcm.cc
> index 94a3ed43aea..03421e490e4 100644
> --- a/gcc/lcm.cc
> +++ b/gcc/lcm.cc
> @@ -56,9 +56,6 @@ along with GCC; see the file COPYING3.  If not see
>  #include "lcm.h"
>  
>  /* Edge based LCM routines.  */
> -static void compute_antinout_edge (sbitmap *, sbitmap *, sbitmap *, sbitmap *);
> -static void compute_earliest (struct edge_list *, int, sbitmap *, sbitmap *,
> -       sbitmap *, sbitmap *, sbitmap *);
>  static void compute_laterin (struct edge_list *, sbitmap *, sbitmap *,
>       sbitmap *, sbitmap *);
>  static void compute_insert_delete (struct edge_list *edge_list, sbitmap *,
> @@ -79,7 +76,7 @@ static void compute_rev_insert_delete (struct edge_list *edge_list, sbitmap *,
>     This is done based on the flow graph, and not on the pred-succ lists.
>     Other than that, its pretty much identical to compute_antinout.  */
>  
> -static void
> +void
>  compute_antinout_edge (sbitmap *antloc, sbitmap *transp, sbitmap *antin,
>         sbitmap *antout)
>  {
> @@ -170,7 +167,7 @@ compute_antinout_edge (sbitmap *antloc, sbitmap *transp, sbitmap *antin,
>  
>  /* Compute the earliest vector for edge based lcm.  */
>  
> -static void
> +void
>  compute_earliest (struct edge_list *edge_list, int n_exprs, sbitmap *antin,
>    sbitmap *antout, sbitmap *avout, sbitmap *kill,
>    sbitmap *earliest)
> diff --git a/gcc/lcm.h b/gcc/lcm.h
> index e08339352e0..7145d6fc46d 100644
> --- a/gcc/lcm.h
> +++ b/gcc/lcm.h
> @@ -31,4 +31,7 @@ extern struct edge_list *pre_edge_rev_lcm (int, sbitmap *,
>     sbitmap *, sbitmap *,
>     sbitmap *, sbitmap **,
>     sbitmap **);
> +extern void compute_antinout_edge (sbitmap *, sbitmap *, sbitmap *, sbitmap *);
> +extern void compute_earliest (struct edge_list *, int, sbitmap *, sbitmap *,
> +       sbitmap *, sbitmap *, sbitmap *);
>  #endif /* GCC_LCM_H */
> 
 
-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)