.. 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.
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.