[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |53947

--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-13 08:50:39 UTC ---
Link to vectorizer missed-optimization meta-bug.

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.5.0

--- Comment #10 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-19 11:41:55 UTC ---
Fixed (predcom is now after the vectorizer, PRE avoids creating such
dependences now).  The enhancement is tracked by PR35229.

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[jessiecute13 at aol dot com]

------- Comment #9 from jessiecute13 at aol dot com  2009-08-17 17:38 -------
$1.21


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[matz at gcc dot gnu dot org]

------- Comment #8 from matz at gcc dot gnu dot org  2009-07-22 15:40 -------
So, the immediate problem is now fixed, but I'd suggest leaving this
enhancement request open, in case anybody wants to work on extending the
vectorizer to deal with these loop-carried dependencies, because in that
case we wouldn't need to dumb down PRE anymore, which would be even better.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[matz at gcc dot gnu dot org]

------- Comment #7 from matz at gcc dot gnu dot org  2009-07-22 15:31 -------
Subject: Bug 39300

Author: matz
Date: Wed Jul 22 15:30:50 2009
New Revision: 149942

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=149942
Log:
        PR tree-optimization/35229
        PR tree-optimization/39300

        * tree-ssa-pre.c (includes): Include tree-scalar-evolution.h.
        (inhibit_phi_insertion): New function.
        (insert_into_preds_of_block): Call it for REFERENCEs.
        (init_pre): Initialize and finalize scalar evolutions.
        * Makefile.in (tree-ssa-pre.o): Depend on tree-scalar-evolution.h .

testsuite/
        * gcc.dg/vect/vect-pre-interact.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/vect-pre-interact.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-pre.c


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[matz at gcc dot gnu dot org]

------- Comment #6 from matz at gcc dot gnu dot org  2009-03-09 13:25 -------
It's also PRE that produces such patterns, so moving predcom behind
vectorization alone won't help this problem.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[dorit at gcc dot gnu dot org]

------- Comment #5 from dorit at gcc dot gnu dot org  2009-03-08 14:25 -------
This is a known problem... Indeed when Zdenek introduced predictive-commoning
there was a discussion on whether to schedule it before or after vectorization.
AFAIR, it ended up getting scheduled before the vectorizer just because this
happened to be what Zdenek tested/experimented with, and he didn't have a
problem with scheduling it after vectorization as long as it didn't hurt
performance (of mgrid in particular). Here are related threads:
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg01383.html
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg00555.html
http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00571.html

Regardless of whether we scheudule predcom after vectorization, it will still
be useful to teach the vectorizer to handle such dependence patterns, as they
may (and do) appear in the source code.  


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[irar at il dot ibm dot com]

------- Comment #4 from irar at il dot ibm dot com  2009-02-25 14:08 -------
Looks similar to PR 35229.

We get here:
# pre.1 = PHI <D.1, D.2>
..
load D.2 
D.3 = D.2 + pre.1 + ...
store D.3


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irar at il dot ibm dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |irar at il dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300

[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-02-25 14:07 -------
Simpler C testcase:

float res[1024], data[1024];

void foo(void)
{
  int i;
  float tmp = data[0];
  for (i = 1; i < 1024; ++i)
    {
      float tmp2 = data[i];
      res[i] = tmp + tmp2;
      tmp = tmp2;
    }
}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300