[ruby-core:96765] [Ruby master Misc#16487] Potential for SIMD usage in ruby-core

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


> 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 pro=
blem 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/pu=
ll/2, and Pavel Rosick=FD experimented on `String#strip` https://github.com=
/ruby/ruby/pull/2815.

### Problem

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

And since most Ruby users use precompiled binaries from repositories and su=
ch, 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 i=
nstructions ? And if so under which conditions.

cc @shyouhei





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