[ruby-core:113237] [Ruby master Bug#4040] SystemStackError with Hash[*a] for Large _a_

Issue #4040 has been updated by ko1 (Koichi Sasada).


Quote from devmeeting agenda https://bugs.ruby-lang.org/issues/19525:

> The fix results in a minor performance decrease in microbenchmarks.

Could you show more details (results)?
Do you have an analysis which line(s) makes slower?

----

I don't think this feature should be rejected. It is cool to support this feature (long splat can be accepted by rest argument).
However, personally speaking I feel the proposed patch (https://github.com/ruby/ruby/pull/7522) is too complex for future maintenance comparing with the benefits from the patch.

Now I have no time to review the patch closely and I couldn't confirm this patch has such issue.
So I agree to merge it (and rewrite them if they can be more improved) because it is well tested.
I think it is better to have benchmark measurements on some benchmarks, though.

General comments:
* Some code are duplicated so maybe they can be more shorter.
* (optimization) It is not sure how the optimization target cases are there (optimizations for the minor cases can introduce issues such as i-cache miss, difficulty on future maintenance and so on).

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Bug #4040: SystemStackError with Hash[*a] for Large _a_
https://bugs.ruby-lang.org/issues/4040#change-102785

* Author: runpaint (Run Paint Run Run)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 1.9.3dev (2010-11-09 trunk 29737) [x86_64-linux] 
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
=begin
 I've been hesitating over whether to file a ticket about this, so please feel free to close if I've made the wrong choice.
 
 I often use Hash[*array.flatten] in IRB to convert arrays of arrays into hashes. Today I noticed that if the array is big enough, this would raise a SystemStackError. Puzzled, I looked deeper. I assumed I was hitting the maximum number of arguments a method's argc can hold, but realised that the minimum size of the array needed to trigger this exception differed depending on whether I used IRB or not. So, presumably this is indeed exhausting the stack...
 
 In IRB, the following is the minimal reproduction of this problem:
 
   Hash[*130648.times.map{ 1 }]; true
 
 I haven't looked for the minimum value needed with `ruby -e`, but the following reproduces:
 
   ruby -e 'Hash[*1380888.times.map{ 1 }]'
 
 I suppose this isn't technically a bug, but maybe it offers another argument for either #666 or an extension of #3131.
=end




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