From: watson1978@...
Date: 2017-04-14T09:04:45+00:00
Subject: [ruby-dev:50078] [Ruby trunk Bug#13368] Improve performance of Array#sum with float elements

Issue #13368 has been updated by watson1978 (Shizuo Fujita).


naruse (Yui NARUSE) wrote:
> Hmm, the result shows clang is not efficient as gcc yet this time.
> And improvement should be done by clang, not us.
> Or should be done by something cleaner patch.

Could you report this to clang developer If you don't want to fix this ?

----------------------------------------
Bug #13368: Improve performance of Array#sum with float elements
https://bugs.ruby-lang.org/issues/13368#change-64230

* Author: watson1978 (Shizuo Fujita)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
The declaration of local variable in loop, it will initialize local variable for each run of the loop with clang generated code.
So, it shouldn't declare the local variable in heavy loop.

Array#sum with float elements will be faster around 30%.

### Before
~~~
       user     system      total        real
   3.320000   0.010000   3.330000 (  3.336088)
~~~

### After
~~~
       user     system      total        real
   2.590000   0.010000   2.600000 (  2.602399)
~~~

### Test code
~~~
require 'benchmark'

Benchmark.bmbm do |x|
  ary = []
  10000.times { ary << Random.rand }

  x.report do
    50000.times do
      ary.sum
    end
  end

end
~~~

### Patch
https://github.com/ruby/ruby/pull/1555



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