[Haskell-cafe] How to make Repa do stencils unboxed?

William Yager will.yager at gmail.com
Sat Jul 2 22:46:58 UTC 2016

OK, some interesting things:

1. INLINE pragmas seem to have no substantial effect.

2. Regrettably, using Dimensional does seem to have some negative effect on
performance. It's about 1.5x slower with Dimensional. The fragility of our
currently used fusion techniques renders empty the promise of
"overhead-free" newtype abstractions.

3. I got a *huge* performance boost by calculating `outputs` through
`runIdentity` rather than treating it as an IO action. Several times
faster. This makes sense, but I'm surprised the results are so drastic.

At this point, `mapStencil2

On Sat, Jul 2, 2016 at 3:46 AM, Ben Lippmeier <benl at ouroborus.net> wrote:

> On 2 Jul 2016, at 1:34 PM, William Yager <will.yager at gmail.com> wrote:
> My code to do this is as follows:
> https://gist.github.com/wyager/8c468c9d18ad62aff8bc9738aa947ea4
> 1) Put INLINE pragmas on all the leaf functions, especially ‘kernel’. If
> the compiler does not inline these functions they won’t fuse. This is a key
> problem with the Repa approach to fusion.
> 2) The ‘dimensional’ packages wraps a data type around all those values.
> I’m not convinced the simplifier will be able to undo the wrapping /
> unwrapping. You’ll need to inspect the core code to check.
> Ben.
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