[ruby-core:121209] [Ruby master Bug#21164] Performance Regression using --jit

28 Feb 2025


      Issue #21164 has been updated by purbug28 (puni ru).


```ruby
# frozen_string_literal: true

require 'benchmark'
n = 200000
time = Benchmark.realtime do
  c = Array.new(n + 1, 0)
  (1..n).each do |i|
    a = []
    m = 100
    (1..m).each do
      a << i
      c[i] += 1
      a << i / m
      c[i % m] += 1
    end
  end
end
puts time
```
I can see the same slowdown with `--disable-gems` and Benchmark.realtime.
```
...
ruby -v --disable-gems --jit array.rb
ruby 3.3.7 (2025-01-15 revision be31f993d7) +YJIT [x86_64-linux]
1.1835691558662802
ruby -v --disable-gems --jit array.rb
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +YJIT +PRISM [x86_64-linux]
1.9472596580162644

----------------------------------------
Bug #21164: Performance Regression using --jit
https://bugs.ruby-lang.org/issues/21164#change-112150

* Author: purbug28 (puni ru)
* Status: Feedback
* ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Ruby 3.4.2 --jit runs slower than no JIT, while Ruby 3.3.7 --jit runs faster.
```ruby
# frozen_string_literal: true
n = 200000
c = Array.new(n + 1, 0)
(1..n).each do |i|
  a = []
  m = 100
  (1..m).each do
    a &lt;&lt; i
    c[i] += 1
    a &lt;&lt; i / m
    c[i % m] += 1
  end
end
puts c.sum

results of /usr/bin/time
ruby 3.4.2
  --jit : 1.98user 0.03system 0:02.02elapsed 99%CPU (0avgtext+0avgdata 19692maxresident)k
  no JIT: 1.77user 0.02system 0:01.80elapsed 99%CPU (0avgtext+0avgdata 18916maxresident)k
ruby 3.3.7
  --jit : 1.20user 0.05system 0:01.26elapsed 99%CPU (0avgtext+0avgdata 23220maxresident)k
  no JIT: 1.81user 0.02system 0:01.83elapsed 99%CPU (0avgtext+0avgdata 22952maxresident)k
  
`ruby -v --jit`
```
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +YJIT +PRISM [x86_64-linux]
```


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