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

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

* Author: watson1978 (Shizuo Fujita)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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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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