From: shyouhei@...
Date: 2017-09-04T04:07:43+00:00
Subject: [ruby-dev:50218] [Ruby trunk Bug#13861] Performance regressoion in Hash literal in Ruby 2.5.0-dev

Issue #13861 has been updated by shyouhei (Shyouhei Urabe).

File tmp2.png added

watson1978 (Shizuo Fujita) wrote:
> 	Hash literal performance -> 35.7 % slow down since Ruby 2.4.1

I have to disagree.

```ruby
require 'benchmark/ips'
n = 32

Benchmark.ips do |x|
  # precalc literals
  lit = []
  (0..n).each{|i|lit[i]="x.report(#{i}){{".dup}
  (0..n).each{|i|(0...i).each{|j|lit[n-j]<< "i#{i}: #{i}, "}}
  (0..n).each{|i|lit[i]<< "}}"}
  bench = lit.join("\n")

  # let's go
  eval bench
end
```

This benchmark yields attached result on my machine.  It is clear that trunk is overall much faster than 2.4.  Hash literals of 3 and 4 elements are the only cases that needs improvements.

----------------------------------------
Bug #13861: Performance regressoion in Hash literal in Ruby 2.5.0-dev
https://bugs.ruby-lang.org/issues/13861#change-66467

* Author: watson1978 (Shizuo Fujita)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.0dev (2017-09-02 trunk 59626) [x86_64-linux]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
Seems Ruby 2.5.0-dev has performance regressoion in Hash literal.
I've confirmed it with below benchmark script

	Hash literal performance -> 35.7 % slow down since Ruby 2.4.1


### Environment
* Ubuntu 17.04
* gcc version 7.0.1


### Ruby 2.5.0-dev

```
$ ./miniruby -v -Ilib -I../benchmark-ips/lib  ~/tmp/bench.rb
ruby 2.5.0dev (2017-09-02 trunk 59626) [x86_64-linux]
/home/watson/tmp/bench.rb:7: warning: assigned but unused variable - hash
/home/watson/tmp/bench.rb:15: warning: assigned but unused variable - string
Warming up --------------------------------------
                Hash    93.650k i/100ms
              String   226.366k i/100ms
Calculating -------------------------------------
                Hash      1.713M (± 0.2%) i/s -      8.616M in   5.030997s
              String     16.477M (± 0.1%) i/s -     82.397M in   5.000892s
```

### Ruby 2.4.1

```
$ ruby -v -Ilib -I../benchmark-ips/lib  ~/tmp/bench.rb
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
/home/watson/tmp/bench.rb:7: warning: assigned but unused variable - hash
/home/watson/tmp/bench.rb:15: warning: assigned but unused variable - string
Warming up --------------------------------------
                Hash   117.135k i/100ms
              String   259.608k i/100ms
Calculating -------------------------------------
                Hash      2.663M (± 0.3%) i/s -     13.353M in   5.014087s
              String     17.259M (± 0.2%) i/s -     86.449M in   5.009036s
```

### Benchmark code

```ruby
require 'benchmark/ips'

Benchmark.ips do |x|
  x.report "Hash" do |loop|
    count = 0
    while count < loop
      hash = {foo: 12, bar: 34, baz: 56}
      count += 1
    end
  end

  x.report "String" do |loop|
    count = 0
    while count < loop
      string = "hello world"
      count += 1
    end
  end
end
```

---Files--------------------------------
tmp2.png (70.4 KB)


-- 
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