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| author | Nadav Rotem <nrotem@apple.com> | 2012-12-19 18:02:36 +0000 |
|---|---|---|
| committer | Nadav Rotem <nrotem@apple.com> | 2012-12-19 18:02:36 +0000 |
| commit | 3e6da7e0dc7f264578203315272721919023a1b1 (patch) | |
| tree | e8ce2f0dbcb2f2b228d74800062f86d3775cfc08 /docs | |
| parent | 91223a41ef0f5b469b1230919cba9012beb6f321 (diff) | |
| download | llvm-3e6da7e0dc7f264578203315272721919023a1b1.tar.gz llvm-3e6da7e0dc7f264578203315272721919023a1b1.tar.bz2 llvm-3e6da7e0dc7f264578203315272721919023a1b1.tar.xz | |
DOC: document the use of O2, O3 and Os with -fvectorize.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170567 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/Vectorizers.rst | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/docs/Vectorizers.rst b/docs/Vectorizers.rst index 84fef67845..9507fd6953 100644 --- a/docs/Vectorizers.rst +++ b/docs/Vectorizers.rst @@ -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. |