Re: Re: [PATCH] DSE: Enhance dse with def-ref analysis

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

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OK. Thank you so much fixing this for me. Would you mind pushing your optimization upstream? 
I will abandon my codes. Thank you so much.



juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2022-09-22 16:48
To: juzhe.zhong@rivai.ai
CC: gcc-patches
Subject: Re: Re: [PATCH] DSE: Enhance dse with def-ref analysis
On Thu, 22 Sep 2022, juzhe.zhong@rivai.ai wrote:
 
> Does your local code exclude my codes?
> I am using GCC12.2. When I delete all my codes and apply your codes only.
> It fails to delete redundant stores and no auto-vecotorization of my RVV GCC in this test. 
> I am not sure whether I am on the same page with you.
 
I applied my patch to GCC master where it handles the testcase
from the PR in the first 042t.dse1 pass.  I have not applied your
patch.  The patch needs an amendment to pass bootstrap,
 
              if (is_gimple_assign (use_stmt))
 
needs to be
 
              if (ref->ref && is_gimple_assign (use_stmt))
 
testing then also reveals
 
XPASS: gcc.dg/vect/tsvc/vect-tsvc-s243.c -flto -ffat-lto-objects  
scan-tree-dump vect "vectorized 1 loops"
XPASS: gcc.dg/vect/tsvc/vect-tsvc-s243.c scan-tree-dump vect "vectorized 1 
loops"
 
I guess that's expected.  Indeed when applying the patch to the
GCC 12 branch the case isn't optimized.  I think it's probably
the PR106019 fix missing, aka r13-1203-g038b077689bb53
 
Richard.
 
> 
> 
> 
> juzhe.zhong@rivai.ai
>  
> From: Richard Biener
> Date: 2022-09-22 16:01
> To: juzhe.zhong@rivai.ai
> Subject: Re: Re: [PATCH] DSE: Enhance dse with def-ref analysis
> On Thu, 22 Sep 2022, juzhe.zhong@rivai.ai wrote:
>  
> > I tried this solution you gave:
> > >> else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
> > >>   {
> > >>       if (is_gimple_assign (use_stmt))
> > >> {
> > >>   data_reference_p dra, drb;
> > >>   dra = create_data_ref (NULL, NULL, ref->ref, stmt,
> > >> false, false);
> > >>   drb = create_data_ref (NULL, NULL,
> > >> gimple_assign_rhs1 (use_stmt),
> > >> use_stmt, false, false);
> > >>   bool alias_p = dr_may_alias_p (dra, drb, NULL);
> > >>   free_data_ref (dra);
> > >>   free_data_ref (drb);
> > >>   if (!alias_p)
> > >>     {
> > >>       if (gimple_vdef (use_stmt))
> > >> defs.safe_push (use_stmt);
> > >>       continue;
> > >>     }
> > >> }
> > 
> > It still fails to delete the redundant store. The reason is when checking the redundant store.
> > it didn't match the condtion: ref_maybe_used_by_stmt_p (use_stmt, ref).
>  
> It does for me:
>  
>   Deleted dead store: a[i_18] = _5;
>  
> ...
>  
>   <bb 3> :
>   _1 = b[i_18];
>   _2 = c[i_18];
>   _3 = d[i_18];
>   _4 = _2 * _3;
>   _5 = _1 + _4;
>   _8 = e[i_18];
>   _9 = _3 * _8;
>   _10 = _5 + _9;
>   b[i_18] = _10;
>   _12 = i_18 + 1;
>   _13 = a[_12];
>   _15 = _3 * _13;
>   _16 = _10 + _15;
>   a[i_18] = _16;
>  
> the other relevant function is stmt_kills_ref_p, that one does
> handle a[i_18] vs. a[i_18] just fine.
>  
> > Maybe we should first figure why it doesn't satisfy this situation?
> > 
> > 
> > juzhe.zhong@rivai.ai
> >  
> > From: Richard Biener
> > Date: 2022-09-22 15:44
> > To: Ju-Zhe Zhong
> > CC: gcc-patches; richard.sandiford
> > Subject: Re: [PATCH] DSE: Enhance dse with def-ref analysis
> > On Thu, 22 Sep 2022, Richard Biener wrote:
> >  
> > > On Thu, 22 Sep 2022, juzhe.zhong@rivai.ai wrote:
> > > 
> > > > From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> > > > 
> > > > This patch fix issue: PR 99407
> > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407
> > > > 
> > > > The enhancement implementation is simple:
> > > > 1.Search gimple statement in program reverse order.
> > > > 2.Queue the store statement which may be possible kill the def
> > > >   of previous store statement.
> > > > 3.Perform dse_def_ref_analysis to remove stores will not kill
> > > >   any def.
> > > >   For example:
> > > >     a[i_18] = _5;
> > > >     ...
> > > >     foo (&a);
> > > >     a[i_18] = _7;
> > > >     
> > > >   a[i_18] = _7 is queued at the begining and will be removed
> > > >   in dse_def_ref_analysis.
> > > > 4.Remove the store if the def is confirmed to be killed.
> > > 
> > > But we already do the very same thing in dse_classify_store, I fail
> > > to see why we need to have an alternate implementation?  It also
> > > seems to be quadratic in the size of a basic-block?
> > > 
> > > The issue with dse_classify_store is that it relies on
> > > ref_maybe_used_by_stmt_p but that doesn't handle
> > > 
> > >  a[i] = ..;
> > >  .. = a[i+1];
> > > 
> > > but when seeing a[_1] vs. a[_2] (two variable offsets), it gives
> > > up, asserting may-aliasing.  We do have infrastructure to catch
> > > such cases with data reference analysis.  If we want to catch
> > > these cases we should use that instead.  Given we have a
> > > DSE/DCE pass pair right before loop optimizations we could even
> > > move those inside of the loop pipeline and perform this more
> > > expensive checks conditional on loop/scev availability.
> >  
> > Oh, and when doing non-loop aware analysis we don't need SCEV.  The
> > following optimizes the testcase but as said I don't think we want
> > to perform this for each of the DSE passes since it can be somewhat
> > expensive, at least without doing more caching (we could keep a
> > stmt -> data-ref hash-map and compute data-refs at most once for each
> > statement, that would make it more acceptable).
> >  
> > Richard.
> >  
> > From 515b213e9d06c2bd36160e66728f57e48095bb84 Mon Sep 17 00:00:00 2001
> > From: Richard Biener <rguenther@suse.de>
> > Date: Thu, 22 Sep 2022 09:40:40 +0200
> > Subject: [PATCH] tree-optimization/99407 - DSE with data-ref analysis
> > To: gcc-patches@gcc.gnu.org
> >  
> > * tree-ssa-dse.c (dse_classify_store): Use data-ref analysis
> > to disambiguate more uses.
> > ---
> > gcc/tree-ssa-dse.cc | 21 +++++++++++++++++++++
> > 1 file changed, 21 insertions(+)
> >  
> > diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
> > index 34cfd1a8802..340a54f4105 100644
> > --- a/gcc/tree-ssa-dse.cc
> > +++ b/gcc/tree-ssa-dse.cc
> > @@ -45,6 +45,8 @@ along with GCC; see the file COPYING3.  If not see
> > #include "ipa-modref.h"
> > #include "target.h"
> > #include "tree-ssa-loop-niter.h"
> > +#include "cfgloop.h"
> > +#include "tree-data-ref.h"
> > /* This file implements dead store elimination.
> > @@ -1019,6 +1021,25 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
> >   /* If the statement is a use the store is not dead.  */
> >   else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
> >     {
> > +       if (is_gimple_assign (use_stmt))
> > + {
> > +   data_reference_p dra, drb;
> > +   dra = create_data_ref (NULL, NULL, ref->ref, stmt,
> > + false, false);
> > +   drb = create_data_ref (NULL, NULL,
> > + gimple_assign_rhs1 (use_stmt),
> > + use_stmt, false, false);
> > +   bool alias_p = dr_may_alias_p (dra, drb, NULL);
> > +   free_data_ref (dra);
> > +   free_data_ref (drb);
> > +   if (!alias_p)
> > +     {
> > +       if (gimple_vdef (use_stmt))
> > + defs.safe_push (use_stmt);
> > +       continue;
> > +     }
> > + }
> > +
> >       /* Handle common cases where we can easily build an ao_ref
> > structure for USE_STMT and in doing so we find that the
> > references hit non-live bytes and thus can be ignored.
> > 
>  
> 
 
-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
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