[Bug middle-end/40384] New: [4.5 regression] Revision 148277 failed 148277

[Bug middle-end/40384] New: [4.5 regression] Revision 148277 failed 148277

[hjl dot tools at gmail dot com]

Revision 148277:

http://gcc.gnu.org/ml/gcc-cvs/2009-06/msg00257.html

caused:

http://gcc.gnu.org/ml/gcc-cvs/2009-06/msg00257.html

We no longer generate prefetch.


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           Summary: [4.5 regression] Revision 148277 failed 148277
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hjl dot tools at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug middle-end/40384] [4.5 regression] Revision 148277 failed 148277

[hjl dot tools at gmail dot com]

------- Comment #1 from hjl dot tools at gmail dot com  2009-06-09 10:24 -------
Caused:

FAIL: gcc.dg/tree-ssa/prefetch-5.c scan-tree-dump-times aprefetch "Issued
prefetch" 2


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug tree-optimization/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |tree-optimization
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug tree-optimization/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[gshobaki at gcc dot gnu dot org]

------- Comment #2 from gshobaki at gcc dot gnu dot org  2009-06-09 22:37 -------
The new cost model added in revision 148277 supresses prefetching in a loop
when it is unlikely to be profitable. One such non-profitable case is a loop
with an unknown trip count and a high prefeching cost. The prefetching cost is
modeled by the ratio between the prefetch count and the total instruction count
in a loop. When this ratio is greater than 1/10 in a loop with an unknown trip
count, prefetching is considered non-profitable and no prefetches are issued.
The first two loops in this test case fall under this category, where the trip
count is not known and the prefetch-to-insn ratio is 1/5. Possible fixes are:

1. Add more computation to the loop bodies in the test case to reduce the
prefetch-to-insn ratios and hence make the loops profitable from the cost
model's point of view.
2. Use a commad line option to set the maximum profitable prefetch-to-insn
ratio to 1/5. The syntax is --param min-insn-to-prefetch-ratio=5
3. Change the expected output such that it does not expect prefetches in this
case.

Any feedback on which one is the preferred solution?

Thanks
-Ghassan



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gshobaki at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gshobaki at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug tree-optimization/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl dot tools at gmail dot com]

------- Comment #3 from hjl dot tools at gmail dot com  2009-06-10 20:14 -------
(In reply to comment #2)
> The new cost model added in revision 148277 supresses prefetching in a loop
> when it is unlikely to be profitable. One such non-profitable case is a loop
> with an unknown trip count and a high prefeching cost. The prefetching cost is
> modeled by the ratio between the prefetch count and the total instruction count
> in a loop. When this ratio is greater than 1/10 in a loop with an unknown trip
> count, prefetching is considered non-profitable and no prefetches are issued.
> The first two loops in this test case fall under this category, where the trip
> count is not known and the prefetch-to-insn ratio is 1/5. Possible fixes are:
> 
> 1. Add more computation to the loop bodies in the test case to reduce the
> prefetch-to-insn ratios and hence make the loops profitable from the cost
> model's point of view.
> 2. Use a commad line option to set the maximum profitable prefetch-to-insn
> ratio to 1/5. The syntax is --param min-insn-to-prefetch-ratio=5
> 3. Change the expected output such that it does not expect prefetches in this
> case.
> 

I prefer #2 since this is a prefetch test.


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hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl dot tools at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug tree-optimization/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl dot tools at gmail dot com]

------- Comment #4 from hjl dot tools at gmail dot com  2009-06-12 05:00 -------
Adding --param min-insn-to-prefetch-ratio=5 works.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug testsuite/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl dot tools at gmail dot com]

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hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|2009-06-12 13:15:49         |2009-06-12 13:16:00
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug testsuite/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl dot tools at gmail dot com]

------- Comment #5 from hjl dot tools at gmail dot com  2009-06-12 13:24 -------
A patch is posted at

http://gcc.gnu.org/ml/gcc-patches/2009-06/msg00964.html


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2009-
                   |                            |06/msg00964.html


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug testsuite/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl at gcc dot gnu dot org]

------- Comment #6 from hjl at gcc dot gnu dot org  2009-06-12 13:38 -------
Subject: Bug 40384

Author: hjl
Date: Fri Jun 12 13:37:50 2009
New Revision: 148431

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=148431
Log:
2009-06-12  H.J. Lu  <hongjiu.lu@intel.com>

        PR testsuite/40384
        * gcc.dg/tree-ssa/prefetch-5.c: Add --param
min-insn-to-prefetch-ratio=5.

Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/tree-ssa/prefetch-5.c


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384

[Bug testsuite/40384] [4.5 regression] Revision 148277 failed gcc.dg/tree-ssa/prefetch-5.c

[hjl dot tools at gmail dot com]

------- Comment #7 from hjl dot tools at gmail dot com  2009-06-13 00:09 -------
Fixed.


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hjl dot tools at gmail dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40384