[ruby-core:113453] [Ruby master Bug#19334] Defining many instance variables and accessing them is slow in Ruby 3.2.0

Issue #19334 has been updated by Dan0042 (Daniel DeLorme).


jemmai (Jemma Issroff) wrote in #note-8:
> We are planning a more permanent fix as well. Our thinking is that after every 50 IV shapes, we could insert a "hash_iv_index_shape," which will have a pointer to an `rb_id_table` which stores iv_name -> index mapping for the previous 50 shapes, and a pointer to the previous "hash_iv_index_shape". This will significantly speed up the case above as well.

I don't really understand this arbitrary limitation on "every 50 IV shapes". If a shape has a `rb_id_table` for lookups, then it can be shared with its parent but not its siblings. So in the case of 100k ivars like the example, we go through 100k shape transitions, and each of those shapes can point to the same lookup table. We need just one big lookup table for a chain of 100k shapes. No?

----------------------------------------
Bug #19334: Defining many instance variables and accessing them is slow in Ruby 3.2.0
https://bugs.ruby-lang.org/issues/19334#change-103033

* Author: mame (Yusuke Endoh)
* Status: Closed
* Priority: Normal
* Assignee: tenderlovemaking (Aaron Patterson)
* Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: UNKNOWN
----------------------------------------
```
class C
  eval("def initialize; #{ (0..100000).map { "@x#{ _1 } = 0; " }.join } end")
  attr_reader :x50000
end
p :start
C.new.x50000
```

This script takes less than one second in Ruby 3.1.3, and does more than ten second in Ruby 3.2.0.

```
$ time ruby -v test.rb
ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
:start

real    0m0.210s
user    0m0.167s
sys     0m0.044s
```

```
$ time ruby -v test.rb
ruby 3.2.0 (2022-12-25 revision a528908271) [x86_64-linux]
:start

real    0m11.026s
user    0m10.950s
sys     0m0.040s
```

This problem is not critical, but is there any room for improvement?



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