[LLVMdev] Loop unrolling opportunity in SPEC's libquantum with profile info

Chandler Carruth chandlerc at google.com
Wed Jan 15 16:41:17 PST 2014

On Wed, Jan 15, 2014 at 4:13 PM, Diego Novillo <dnovillo at google.com> wrote:

> Chandler also pointed me at the vectorizer, which has its own
> unroller. However, the vectorizer only unrolls enough to serve the
> target, it's not as general as the runtime-triggered unroller. From
> what I've seen, it will get a maximum unroll factor of 2 on x86 (4 on
> avx targets). Additionally, the vectorizer only unrolls to aid
> reduction variables. When I forced the vectorizer to unroll these
> loops, the performance effects were nil.

I just also want to point out that we should really be *vectorizing* this
loop as well. It's a great candidate for it AFAICS....
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