[Bug c++/35117] Vectorization on power PC

["victork at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #22 from victork at gcc dot gnu dot org  2008-02-10 15:06 -------
1. It looks like vectorizer was enabled in both cases, since -O3 enables the
vectorizer by the default. You need to add -fno-tree-vectorize to disable it
explicitly.

2. To get better results from vectorized version I would recommend to allocate
arrays at boundaries aligned to 16 byte and let to the compiler to know this.
You can do it by static allocation of arrays:

  float pSum1[64000] __attribute__ ((__aligned__(16)));
  float pSum[64000] __attribute__ ((__aligned__(16)));
  float pVec1[64000] __attribute__ ((__aligned__(16)));

3. It would be better if "itBegin" will start from 0 and be known at compile
time. This and [2] will allow to vectorizer to save realigning loads.

4. For some strange reason the run time of this test can vary significantly (up
to 50%) from run to run. So be sure to run it several times.

-- Victor.


-- 

victork at gcc dot gnu dot org changed:

           What    |Removed                     |Added
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                 CC|                            |victork at gcc dot gnu dot
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35117