[ruby-core:98197] [Ruby master Bug#16840] Why is Ruby getting slower in every version?

Issue #16840 has been reported by ana06 (Ana Maria Martinez Gomez).

----------------------------------------
Bug #16840: Why is Ruby getting slower in every version?
https://bugs.ruby-lang.org/issues/16840

* Author: ana06 (Ana Maria Martinez Gomez)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
I was playing around with Ruby hashing and I have discovered something stra=
nge/surprising.

The file ``test.rb`` looks like:

```ruby

require 'benchmark'
$N =3D 100000

class Ana =

end

objects =3D Array.new($N) { Ana.new() }
hash =3D {}
puts Benchmark.measure { 100.times { objects.each { |obj| hash[obj] =3D tru=
e } }}
```

I executed ``test.rb`` with different Ruby versions and it takes longer wit=
h newer versions. There is 1.5 seconds difference between Ruby 2.5 and mast=
er. Is that expected? And if so, why? Those are the execution results:

```
> rbenv shell 2.5.0
> ruby -v
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
> ruby test.rb
  2.236504   0.003546   2.240050 (  2.240256)
> ruby test.rb
  2.247041   0.003680   2.250721 (  2.250860)
> ruby test.rb
  2.276305   0.000351   2.276656 (  2.276829)
>=B7
> rbenv shell 2.6.2
> ruby -v
ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-linux]
> ruby test.rb
  2.579052   0.004181   2.583233 (  2.583541)
> ruby test.rb
  2.580179   0.000000   2.580179 (  2.580362)
> ruby test.rb
  2.646516   0.000441   2.646957 (  2.647398)
>=B7
> rbenv shell 2.7.1
> ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
> ruby test.rb
  2.915415   0.004209   2.919624 (  2.920206)
> ruby test.rb
  2.867767   0.007511   2.875278 (  2.875416)
> ruby test.rb
  2.877741   0.000410   2.878151 (  2.878431)
>=B7
> rbenv shell 2.8.0-dev
> ruby -v
ruby 2.8.0dev (2020-05-07T16:22:38Z master 7ded8fd29a) [x86_64-linux]
> ruby test.rb
  3.840961   0.007852   3.848813 (  3.849499)
> ruby test.rb
  3.748391   0.007833   3.756224 (  3.756520)
> ruby test.rb
  3.686487   0.001656   3.688143 (  3.688332)
```




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