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DOC: document the use of O2, O3 and Os with -fvectorize. 

llvm-svn: 170567
This commit is contained in:
Nadav Rotem 2012-12-19 18:02:36 +00:00
parent c55c6fc6e3
commit 8f4a6cced2
1 changed files with 6 additions and 2 deletions
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8
llvm/docs/Vectorizers.rst
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@ -18,7 +18,11 @@ command line flag:
.. code-block:: console
$ clang -fvectorize file.c
$ clang -fvectorize -O3 file.c
If the ``-fvectorize`` flag is used then the loop vectorizer will be enabled
when running with ``-O3``, ``-O2``. When ``-Os`` is used, the loop vectorizer
will only vectorize loops that do not require a major increase in code size.
We plan to enable the Loop Vectorizer by default as part of the LLVM 3.3 release.
@ -194,7 +198,7 @@ Performance
This section shows the the execution time of Clang on a simple benchmark:
`gcc-loops <http://llvm.org/viewvc/llvm-project/test-suite/trunk/SingleSource/UnitTests/Vectorizer/>`_.
This benchmarks is a collection of loops from the GCC autovectorization
`page <http://gcc.gnu.org/projects/tree-ssa/vectorization.html>`_ by Dorit Nuzman._
`page <http://gcc.gnu.org/projects/tree-ssa/vectorization.html>`_ by Dorit Nuzman.
The chart below compares GCC-4.7, ICC-13, and Clang-SVN at -O3, running on a Sandybridge.
The Y-axis shows time in msec. Lower is better.