Ruby

Given this script:

class Foo def initialize(**kwargs) end end class Bar def initialize(y:) end end b = GC.stat[:total_allocated_objects] 1000.times { Foo.new(y:1) } p GC.stat[:total_allocated_objects]-b b = GC.stat[:total_allocated_objects] 1000.times { Bar.new(y:1) } p GC.stat[:total_allocated_objects]-b 

On Ruby 3.2 it prints

 (fable-3_3_dead_with_patches) $ ruby --version ruby 3.2.3 (2024-01-18 revision 52bb2ac0a6) [arm64-darwin23] (fable-3_3_dead_with_patches) $ ruby hi.rb 3006 2005 

On Ruby 3.3 it prints:

 ((HEAD detached at v3_3_0)) $ ./ruby --version ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin23] ((HEAD detached at v3_3_0)) $ ./ruby hi.rb 3008 3005 

On master:

 (master) $ git rev-parse HEAD 83618f2cfa004accdd1514de7dcbba291aa7e831 (master) $ ./ruby --version ruby 3.4.0dev (2024-03-14T12:33:30Z master 83618f2cfa) [arm64-darwin23] (master) $ ./ruby hi.rb 3006 4005 

so that is: since Ruby 3.2 .newing an object with static keyword args has grown from 2 allocations per object to 4 allocations per object.

I have a pull request which introduces a new instruction to the VM opt_new which basically inlines calling allocate and initialize directly, avoiding a lot of what is causing these extra objects to be allocated. My PR is here: https://github.com/ruby/ruby/pull/10254. With my patch the script prints 2006 and 1005 respectively. This is the smallest number of objects that can be allocated for such calls.