On Wed, 1 Apr 2020 at 02:49, Alexis King
I’ve been trying to figure out if it would be possible to help the optimizer out by annotating the program with special combinators like the existing ones provided by GHC.Magic. However, I haven’t been able to come up with anything yet that seems like it would actually work.
You may want to take a look at https://github.com/composewell/fusion-plugin which uses annotations to help GHC fuse, not specifically what you want but might possibly be relevant to your work. https://github.com/composewell/streamly relies heavily on case-of-case and SpecConstr for stream fusion. There are several cases that GHC is unable to fuse currently. We use a "Fuse" annotation to tell GHC that any function involving this type must be inlined so that fusion can occur reliably. With the help of fusion-plugin we have been able to fuse almost every known case in streamly till now. -harendra