[ruby-core:114904] [Ruby master Bug#19875] Ruby 3.0 -> 3.1 Performance regression in String#count

Issue #19875 has been updated by ahorek (Pavel Rosick=FD).





I think if the platform support is sufficient, there are multiple places wh=
ere this feature could be beneficial. Even without explicit SIMD code, some=
 existing C code could be autovectorized by the compiler itself for the AVX=
2 target while keeping the binary compatibility with platforms that don't s=
upport these instructions. You can always recompile Ruby with optimization =
flags for your own platform, but most users use precompiled binaries that c=
an't benefit from it now.



could prepare a proof of concept PR for the Ruby repo?



also, see the previous discussion #16487 there are already other existing e=
xamples where this feature could help.



----------------------------------------

Bug #19875: Ruby 3.0 -> 3.1 Performance regression in String#count

https://bugs.ruby-lang.org/issues/19875#change-104770



* Author: iz (Illia Zub)

* Status: Open

* Priority: Normal

* ruby -v: 3.2.2

* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

----------------------------------------

`String#count` became slower since Ruby 3.1. Originally found by `@Freaky`:=
 https://github.com/ruby/ruby/pull/4001#issuecomment-1714779781



Compared using the [`benchmark-driver` gem](https://github.com/benchmark-dr=
iver/benchmark-driver).



```

$ benchmark-driver tmp/string_count_benchmark_driver.yml --rbenv '3.1.1;3.1=
.4;2.7.2;3.2.2;3.0.6'                                                =20

Calculating -------------------------------------

                          3.1.1       3.1.4       2.7.2       3.2.2       3=
.0.6

               count    465.804     463.741     865.783     462.711     857=
.395 i/s -     10.000k times in 21.468251s 21.563768s 11.550239s 21.611783s=
 11.663235s



Comparison:

                            count

               2.7.2:       865.8 i/s=20

               3.0.6:       857.4 i/s - 1.01x  slower

               3.1.1:       465.8 i/s - 1.86x  slower

               3.1.4:       463.7 i/s - 1.87x  slower

               3.2.2:       462.7 i/s - 1.87x  slower

```



Benchmark:





```yml

$ cat ./tmp/string_count_benchmark_driver.yml=20

loop_count: 10_000

prelude: |

  html =3D "\nruby\n" * 1024 * 1024

benchmark:

  count: html.count($/)

```



---



*Initially, I noticed the difference between `str.count($/)` and `str.lines=
.size` when working on the performance improvement: https://serpapi.com/blo=
g/lines-count-failed-deployments/*



---Files--------------------------------

rb_str_len.fast (31.9 KB)

rb_str_len.slow (34 KB)

revert-4001.patch (1.71 KB)

rb_str_count.S (11.8 KB)

bytecount.c (7.23 KB)





--=20

https://bugs.ruby-lang.org/

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