[LLVMdev] Loop vectorizer

Preston Briggs preston.briggs at gmail.com
Tue Oct 16 12:23:29 PDT 2012

Nadav Rotem <nrotem at apple.com> wrote:
> I sent a patch to llvm-commit with a new loop vectorizer.
> This is a very simple loop vectorizer, but we have to start somewhere.
> With this new loop vectorizer we can already vectorize a good number of loops.
> I know that we can improve the new loop vectorizer in a number of ways.
> We can implement a precise dependence test,
> we can add support for reduction variables,
> we can resolve a number of phase-ordering issues, just to name a few.
>  I would like to focus on the 'cost model' aspects of the vectorization.
> In order to implement an efficient cost model we will need to improve
> our codegen infrastructure and implement the VectorTargetTransformationInfo interface.
> I appreciate any help, feedback, patches and ideas on the new loop vectorizer
> and how we can push this forward.

 I'd start by making a plan (a design!) with goals and stuff.
Publish it so we can see what you mean by "vectorization".
I.e., do you mean for real vector machines, a la Cray, or for
the packed media instructions that are currently so popular?

What's your idea for finding vectorizable loops?
Do you have a plan for xforms to increase the amount of vectorization?
What books, papers, theses are you looking at
(so we can get on the same page)?

I've written a dependence analyzer that ought to be suitable
(if it isn't, we should fix it).


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