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

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 be=
nchmark, but the impact of real world application. For example a proposal s=
hould show the change improves the performance of Rails application. Note t=
hat SIMD can improve performance of long strings but usually most string ar=
e 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?

----------------------------------------
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: =

----------------------------------------
### 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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