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2016 May 07
2
About Clang llvm PGO
...ization. Note
that trunk GCC does not turn on vectorization at O2, but O3 or O2 with PGO.
LLVM also vectorizes the key loops. However compared with GCC's vectorizor,
LLVM's auto-vectorizer produces worse code (e.g, long sequence of
instructions to do sign extension etc): ~6.5instr/iter vs ~9instr/iter.
GCC also does loop unroll after vectorization which also helped a little
more. LLVM's vectorization actually hurts performance a little.
We will look into this issue.
thanks,
David
On Fri, May 6, 2016 at 2:04 PM, Jie Chen <Jie.Chen at mathworks.com> wrote:
> Hi David,
>...