[Bug tree-optimization/41879] New: [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[Bug tree-optimization/41879] New: [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

The fix for PR41783 causes us to vectorize RESID and PSINV where we only
predictive common the epilogue loop now.  This causes mgrid score to drop
by almost 40% on x86_64 and the vectorized code is pretty bad because it
uses unaligned accesses.


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           Summary: [4.5 Regression] 172.mgrid regression, vectorizer
                    prevents predictive commoning
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 41783
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-10-30 16:57 -------
Testcase:

      SUBROUTINE PSINV(R,U,C)
      PARAMETER (N=64)
      REAL*8 U(N,N,N),R(N,N,N),C(0:3)
      INTEGER I3, I2, I1
C
      DO 600 I3=2,N-1
      DO 600 I2=2,N-1
      DO 600 I1=2,N-1
 600  U(I1,I2,I3)=U(I1,I2,I3)
     >      +C(0)*( R(I1,  I2,  I3  ) )
     >      +C(1)*( R(I1-1,I2,  I3  ) + R(I1+1,I2,  I3  )
     >           +  R(I1,  I2-1,I3  ) + R(I1,  I2+1,I3  )
     >           +  R(I1,  I2,  I3-1) + R(I1,  I2,  I3+1) )
     >      +C(2)*( R(I1-1,I2-1,I3  ) + R(I1+1,I2-1,I3  )
     >           +  R(I1-1,I2+1,I3  ) + R(I1+1,I2+1,I3  )
     >           +  R(I1,  I2-1,I3-1) + R(I1,  I2+1,I3-1)
     >           +  R(I1,  I2-1,I3+1) + R(I1,  I2+1,I3+1)
     >           +  R(I1-1,I2,  I3-1) + R(I1-1,I2,  I3+1)
     >           +  R(I1+1,I2,  I3-1) + R(I1+1,I2,  I3+1) )
     >      +C(3)*( R(I1-1,I2-1,I3-1) + R(I1+1,I2-1,I3-1)
     >           +  R(I1-1,I2+1,I3-1) + R(I1+1,I2+1,I3-1)
     >           +  R(I1-1,I2-1,I3+1) + R(I1+1,I2-1,I3+1)
     >           +  R(I1-1,I2+1,I3+1) + R(I1+1,I2+1,I3+1) )
C
      RETURN
      END


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-10-30 17:00 -------
With vectorization enabled I get

Running /home/richard/src/trunk/gcc/testsuite/gcc.dg/tree-ssa/tree-ssa.exp ...
FAIL: gcc.dg/tree-ssa/predcom-1.c scan-tree-dump-times pcom "looparound ref" 1
FAIL: gcc.dg/tree-ssa/predcom-4.c scan-tree-dump-times pcom "Combination" 1
FAIL: gcc.dg/tree-ssa/predcom-4.c scan-tree-dump-times pcom "Unrolling 3
times." 1

that is, all predictive commoning tests run with -O2 only...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Priority|P3                          |P2
   Last reconfirmed|0000-00-00 00:00:00         |2009-11-09 13:03:36
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[irar at il dot ibm dot com]

------- Comment #3 from irar at il dot ibm dot com  2009-11-10 10:02 -------
(In reply to comment #0)
> This causes mgrid score to drop
> by almost 40% on x86_64 and the vectorized code is pretty bad because it
> uses unaligned accesses.

Is the vectorized code worse than the scalar one even without predcom?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2009-11-11 20:38 -------
I didn't check yet.  We'll work on a simple cost-model integration of
predcom.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[irar at il dot ibm dot com]

------- Comment #5 from irar at il dot ibm dot com  2009-11-12 07:51 -------
(In reply to comment #4)
> I didn't check yet.  We'll work on a simple cost-model integration of
> predcom.

You mean, vectorizer cost model will take predcom into account?

If the vectorization is not profitable (vs. scalar without predcom), it can be
a matter of vectorizer cost model tuning (looks easier).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2009-11-12 15:17 -------
The idea is to call predcom analysis and hook it into the vectorizer as another
vectorization form for the cost model.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2010-01-19 16:20 -------
Fixed by

Author: matz
Date: Tue Jan 19 16:05:57 2010
New Revision: 156043

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=156043


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-01-20 11:42 -------
mgrid now miscompares on i?86 ...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[matz at gcc dot gnu dot org]

------- Comment #9 from matz at gcc dot gnu dot org  2010-01-20 14:42 -------
See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35418#c8


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[steven at gcc dot gnu dot org]

------- Comment #10 from steven at gcc dot gnu dot org  2010-01-20 15:25 -------
Is there an alt.src for this from SPEC?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879

[Bug tree-optimization/41879] [4.5 Regression] 172.mgrid regression, vectorizer prevents predictive commoning

[rguenther at suse dot de]

------- Comment #11 from rguenther at suse dot de  2010-01-20 15:31 -------
Subject: Re:  [4.5 Regression] 172.mgrid
 regression, vectorizer prevents predictive commoning

On Wed, 20 Jan 2010, steven at gcc dot gnu dot org wrote:

> ------- Comment #10 from steven at gcc dot gnu dot org  2010-01-20 15:25 -------
> Is there an alt.src for this from SPEC?

I don't think so - SPEC 2000 is no longer officially maintained.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41879