[ruby-core:74832] [Ruby trunk Bug#10015] Performance regression in Dir#[]

Issue #10015 has been updated by Layon Ferreira.

ruby -v changed from ruby 2.2.0dev (2014-02-04 trunk 44802) [x86_64-darwin13.0] to ruby 2.3.0 [x86_64-darwin13.0]
Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN to 2.0.0: UNKNOWN, 2.3: UNKNOWN

The problem seems to persist Mac OS X, although is better on 2.3.0, is still a lot slower than 2.1.x.
I have run the benchmark 

    require "benchmark"
    time = []
    5.times do
      result = Benchmark.realtime { 800000.times do Dir['/tmp'] end }
      puts result
      time << result
    end
    average = time.inject{ |sum, el| sum + el }.to_f / time.size    

    puts "average of: #{average}"

On this machine:

```
ProductName:	Mac OS X
ProductVersion:	10.11.4
BuildVersion:	15E65

File System Personality:  Case-sensitive Journaled HFS+
Type (Bundle):            hfs
Name (User Visible):      Mac OS Extended (Case-sensitive, Journaled)
Journal:                  Journal size 40960 KB at offset 0xe8e000
Owners:                   Enabled

```

On the all releases after 2.1.7 and got this results:

```
=====================================================
2.1.7: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.1.7
2.86774
3.012784
2.867388
2.873973
3.127474
average of: 2.9498717999999995
=====================================================
2.1.8: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.1.8
3.095918
2.981513
2.998208
3.142286
3.048603
average of: 3.0533056000000003
=====================================================
2.1.9: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.1.9
3.022291
2.983054
2.931454
2.944659
3.051114
average of: 2.9865144
=====================================================
2.2.0: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.2.0
4.985971766000148
5.047520838999844
5.066739754000082
5.005606599001112
5.0079711159996805
average of: 5.022762014800174
=====================================================
2.2.1: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.2.1
5.0500176069999725
5.031266175999917
5.011832148000394
5.043594308999673
5.0333263849988725
average of: 5.034007324999766
=====================================================
2.2.2: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.2.2
4.983856856000784
4.975439867999739
5.112457198998527
4.985339404000115
4.961809472000823
average of: 5.003780559799997
=====================================================
2.2.3: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.2.3
4.832416973000363
4.970395954000196
5.007825999999113
4.891315167000357
4.913950877999014
average of: 4.923180994399809
=====================================================
2.2.4: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.2.4
5.083285558999705
5.07147571600035
5.153286901999309
5.110161799999332
5.192000732999077
average of: 5.122042141999555
=====================================================
2.3.0: benchmarking
=====================================================
Using /Users/admin/.rvm/gems/ruby-2.3.0
3.785227087999374
3.9434133479990123
4.052104171998508
3.844644614999197
3.88892919600039
average of: 3.9028636837992963
```

----------------------------------------
Bug #10015: Performance regression in Dir#[]
https://bugs.ruby-lang.org/issues/10015#change-57959

* Author: Aaron Patterson
* Status: Closed
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0 [x86_64-darwin13.0]
* Backport: 2.0.0: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
r44802 seems to have introduced a performance regression in Dir#[].

Here is the test program:

~~~ruby
require 'benchmark'

puts Benchmark.realtime {
  glob = "minitest/*_plugin.rb{,.rb,.bundle}"
  $LOAD_PATH.map { |load_path|
    Dir["#{File.expand_path glob, load_path}"]
  }.flatten.select { |file| File.file? file.untaint }
}
~~~

Here is the test time for me:

~~~
$ ruby -v test.rb
ruby 2.2.0dev (2014-02-04 trunk 44801) [x86_64-darwin13.0]
0.000341
$ ruby -v test.rb
ruby 2.2.0dev (2014-02-04 trunk 44802) [x86_64-darwin13.0]
0.009333
~~~

r44801 seems much faster than r44802.



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