[ruby-core:88594] [Ruby trunk Feature#15010] Reduce allocation for rest parameters

Issue #15010 has been updated by chopraanmol1 (Anmol Chopra).


Limitation of patch 2. 

1. Patch 2 gets slower than Patch 1 for a large array. Array with length 100 - 200 have similar performance but beyond that patch 1 is faster in most of the case. 

2. Patch 2 results in segmentation fault for following: https://github.com/ruby/ruby/blob/8e66ffc1d756c42ee025a56672ad71f2200ca6be/test/ruby/test_method.rb#L951


Ignoring above limitation patch 2 do perform better for the small array. One Hack Solution can be to check the length of splat arg against some arbitrary number to decide if splat arg should be expanded to args->argv or should be assigned to args->rest. But it doesn't sound like a nice solution.

----------------------------------------
Feature #15010: Reduce allocation for rest parameters
https://bugs.ruby-lang.org/issues/15010#change-73650

* Author: chopraanmol1 (Anmol Chopra)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Currently multiple arrays are allocated while making a call to method with rest parameter.

E.g.
~~~
def rest_method(*args) #-> This will create 2 arrays
end

def post_method(*args,last) #-> This will create 3 arrays
end
~~~

Applying following set of changes will reduce creation of array to 1

https://github.com/ruby/ruby/pull/1935

Benchmark Result:

trunk
~~~
                                  user     system      total        real
benchmark_method              0.340000   0.000000   0.340000 (  0.337035)
rest_method                   0.964000   0.000000   0.964000 (  0.964660)
lead_method                   0.976000   0.000000   0.976000 (  0.976011)
post_method                   2.424000   0.000000   2.424000 (  2.421732)
lead_post_method              1.800000   0.000000   1.800000 (  1.799500)
rest_with_named_parameter     2.040000   0.000000   2.040000 (  2.040323)
lead_proc underflow_args      1.224000   0.000000   1.224000 (  1.225237)
opt_post_proc overflow_args   1.056000   0.000000   1.056000 (  1.057402)
~~~

modified
~~~
                                  user     system      total        real
benchmark_method              0.336000   0.000000   0.336000 (  0.336911)
rest_method                   0.708000   0.000000   0.708000 (  0.706142)
lead_method                   0.720000   0.000000   0.720000 (  0.717971)
post_method                   1.896000   0.000000   1.896000 (  1.894426)
lead_post_method              1.560000   0.000000   1.560000 (  1.560495)
rest_with_named_parameter     1.464000   0.000000   1.464000 (  1.467313)
lead_proc underflow_args      0.864000   0.000000   0.864000 (  0.863980)
opt_post_proc overflow_args   0.772000   0.000000   0.772000 (  0.770364)
~~~

---Files--------------------------------
bench_method_arg.rb (1.32 KB)
Reduce-allocation-for-rest-parameters-v2.patch (3.57 KB)
Reduce-allocation-for-rest-parameters-v1.patch (7.73 KB)
bench_method_arg_v2.rb (3.15 KB)


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