Issue #18042 has been reported by motoroller (Iskandar Gohar).

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Feature #18042: YARV code optimization
https://bugs.ruby-lang.org/issues/18042

* Author: motoroller (Iskandar Gohar)
* Status: Open
* Priority: Normal
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Hi! Long period of time I think about programmatically code optimization for YARV. In compiled languages like C/C++ the compiler can do whatever it wants with the code and does for performance optimization. Firstly, ruby developers think about code readability, secondary about performance. Because ruby translates .rb file into bytecode we can do whit this bytecode anything to win in performance and do not lose in the expressiveness of the code.

But I came to the conclusion that a static bytecode optimizer is not possible, because in translation stage we don't know about which object/class we use. So, did someone think about runtime code analyzing? If we have some type of statistic we can dynamically transform bytecode to optimized version, use optimized version of C functions. Also I thought if we have statistic we can reduce some GC overhead 

```ruby
# before 
array.map(&:method1).map(&:method2)

# if I know for sure that map is not overridden and calls from Enumerable I can rebuild code like this
array.map do
  _1.method1
  _1.method2
end
```

In this example 2 `map` calls generate one redundant array which will be destructed by GC, so we can transform it to seconds version. It can be applied not only for `map/select` functions, but many other. 

What do you think about it?




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