[llvm] r211888 - [x86] Begin a significant overhaul of how vector lowering is done in the

[Chandler Carruth]

On Fri, Jun 27, 2014 at 6:54 PM, Nadav Rotem <nrotem at apple.com> wrote:

> Hi Chandler,
>
> Thank you for working on this. Lowering shuffles on X86 is challenging and
> I am glad that you are rewriting and improving this code. Everything looks
> great.
>
> >
> > Once SSE2 is polished a bit I should be able to get interesting numbers
> > on performance improvements on benchmarks conducive to vectorization.
> > All of this will be off by default until it is functionally equivalent
> > of course.
>
> I was wondering how you plan to benchmark this code. The vectorizers don’t
> generate interesting shuffle pattern (mainly reverse and broadcast)
>

My work here is motivated specifically by shuffles generated by the
vectorizer, so I'm not sure why you think they don't generate interesting
shuffle patterns.


> and traditionally interesting shuffle patterns came from hand written code
> and from code in the domain of graphics, like OpenCL, OpenGL and ISPC. Is
> there a specific benchmark that you think could be useful?
>

I have a decent number of both hand vectorized code and code which
vectorizes well; I expect to be able to get reasonable baseline benchmarks
from this.

Also, it is pretty easy to look at the output before and after and
understand pretty clearly the likely performance characteristics.
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