[ruby-core:96842] [Ruby master Misc#16487] Potential for SIMD usage in ruby-core

[naruse@airemix.jp]

Issue #16487 has been updated by naruse (Yui NARUSE).


Remaining topic is
* What function should use SIMD. It should be decided based on not micro benchmark, but the impact of real world application. For example a proposal should show the change improves the performance of Rails application. Note that SIMD can improve performance of long strings but usually most string are short. If a change is optimized for longer strings, it sometimes slow for short strings. Such optimization are not acceptable.
* How to coordinate configure and ifdefs. What is the default behavior? How to specify to use SIMD?

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Misc #16487: Potential for SIMD usage in ruby-core
https://bugs.ruby-lang.org/issues/16487#change-83845

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