[Bug target/27855] reassociation pass produces ~30% slower matrix multiplication code

[ubizjak at gmail dot com]

------- Comment #15 from ubizjak at gmail dot com  2007-07-09 18:16 -------
New timings on x86_64 core2 (from [1])

The tests were performed on core2 in 64bit mode, using '-DREPS=10000 -O3 -msse3
-march=core2 -ffast-math' flags, with and without newly introduced
-fno-tree-reassoc flag.

The results were _interesting_, showing extreme differences in the run times:

w/o -fno-tree-reassoc:

ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

-DTYPE=float:     atlasmm       60  10000       2.000     2159.87
-DTYPE=double:    atlasmm       60  10000       2.500     1727.89

w/ -fno-tree-reassoc:

ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

-DTYPE=float:     atlasmm       60  10000       0.932     4634.90
-DTYPE=double:    atlasmm       60  10000       1.520     2841.93

[1] http://gcc.gnu.org/ml/gcc-patches/2007-07/msg00849.html


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27855