[ruby-core:113258] [Ruby master Bug#4040] SystemStackError with Hash[*a] for Large _a_

Issue #4040 has been updated by jeremyevans0 (Jeremy Evans).


I rebased my branch against master, and then ran all of the `app_*` benchmarks, here are the results:

```
app_aobench: +1%
app_erb: 0%
app_factorial: 0%
app_fib: +5%
app_lc_fizzbuzz: 0%
app_mandelbrot: 0%
app_pentomino: -1%
app_raise: 0%
app_strconcat: +8%
app_tak: +4%
app_tarai: +3%
app_uri: -2%
```

For most of the benchmarks, I ran with `--repeat-count 10 --repeat-result best` (some take a long time and I only ran with 1 or 3 instead of 10).

So from this benchmarking, only `app_pentomino` and `app_uri` are slower, by 1-2%.  5 benchmarks are faster, by up to 8%. 5 benchmarks did not show any performance differences.

`app_fib` is showing up 5% faster now, when it was previously showing 1-3% slower.  To make sure this wasn't an anomaly, I ran with `--repeat-count 25`, and still got the same results. Again, this could just be due to my environment (OpenBSD), as I cannot think of a reason why `app_fib` would be faster with the changes.

All of these benchmarks are more of the microbenchmark nature.  More realistic benchmarks such as yjit-bench on Linux would be better for testing actual differences in performance.

----------------------------------------
Bug #4040: SystemStackError with Hash[*a] for Large _a_
https://bugs.ruby-lang.org/issues/4040#change-102814

* 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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