From: pdahorek@...
Date: 2020-01-10T14:12:58+00:00
Subject: [ruby-core:96765] [Ruby master Misc#16487] Potential for SIMD usage	in ruby-core

Issue #16487 has been updated by ahorek (Pavel Rosick�).


> use __target__ attributes

thanks for the links, very helpful

> It's unfortunate the C compiler cannot do this on its own.

yes, sometimes it's possible and it would be great, but
1/ it requires a lot of effort to convince the compiler to do what you want. It's basically about good data structures and alignments
2/ performance is usually worse
3/ if you care about readability than such code is even less readable

I don't think maintenance is a big deal. I'm more worried about code bloat, having many functions (c, sse2, avx2 version etc...) to solve the same problem isn't DRY.

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Misc #16487: Potential for SIMD usage in ruby-core
https://bugs.ruby-lang.org/issues/16487#change-83759

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
### Context

There are several ruby core methods that could be optimized with the use of SIMD instructions.

I experimented a bit on `coderange_scan` https://github.com/Shopify/ruby/pull/2, and Pavel Rosick� experimented on `String#strip` https://github.com/ruby/ruby/pull/2815.

### Problem

The downside of SIMD instructions is that they are not universally available.
So it means maintaining several versions of the same code, and switching them either statically or dynamically.

And since most Ruby users use precompiled binaries from repositories and such, it would need to be dynamic if we want most users to benefit from it.

So it's not exactly "free speed", as it means a complexified codebase.

### Question

So the question is to know wether ruby-core is open to patches using SIMD instructions ? And if so under which conditions.

cc @shyouhei





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