[Bug target/40648] New: misaligned store vectorizer patch introduced 10% runtime regression on Polyhedron test_fpu

[ubizjak at gmail dot com]

Hello!

The "[patch, vectorizer] misaligned store support" patch [1] resulted in more
than 10% longer execution time for Polyhedron test_fpu test on Core2.

The test is compiled with "-march=x86-64 -ffast-math -funroll-loops -O3",
results are:

time ./a.out
  Benchmark running, hopefully as only ACTIVE task
Test1 - Gauss 2000 (101x101) inverts  2.5 sec  Err= 0.000000000000006
Test2 - Crout 2000 (101x101) inverts  2.5 sec  Err= 0.000000000000015
Test3 - Crout  2 (1001x1001) inverts  2.3 sec  Err= 0.000000000000065
Test4 - Lapack 2 (1001x1001) inverts  2.4 sec  Err= 0.000000000000250
                             total =  9.6 sec


real    0m9.864s
user    0m9.778s
sys     0m0.074s

with patch [1] included, vs.:

time ./a.out
  Benchmark running, hopefully as only ACTIVE task
Test1 - Gauss 2000 (101x101) inverts  1.9 sec  Err= 0.000000000000006
Test2 - Crout 2000 (101x101) inverts  2.5 sec  Err= 0.000000000000015
Test3 - Crout  2 (1001x1001) inverts  2.3 sec  Err= 0.000000000000065
Test4 - Lapack 2 (1001x1001) inverts  2.0 sec  Err= 0.000000000000250
                             total =  8.6 sec


real    0m8.869s
user    0m8.788s
sys     0m0.068s

when patch [1] is reverted.

The compiler is from today's SVN, "xgcc (GCC) 4.5.0 20090704 (experimental)
[trunk revision 149223]".

The effect of this patch can also be seen on [2], see test_fpu chart between
2009-06-05 and 2009-06-06.

[1] http://gcc.gnu.org/ml/gcc-patches/2009-06/msg00492.html
[2] http://gcc.opensuse.org/c++bench/polyhedron/polyhedron-summary.txt-2-0.html


-- 
           Summary: misaligned store vectorizer patch introduced 10% runtime
                    regression on Polyhedron test_fpu
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ubizjak at gmail dot com
 GCC build triplet: x86_64-pc-linux-gnu
  GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40648