bench_ivar_set2.rb

require 'benchmark/ips'

# initialized
class A
  def initialize
    @c = @d = @e = @f = @g = @h = nil
  end
  def read
    @c || @d || @e || @f || @g || @h
  end
end

# not initialized
class B
  def initialize
    # nothing
  end
  def read
    @c || @d || @e || @f || @g || @h
  end
end

# later initialized
class C
  def initialize
    # nothing
  end
  def read
    @c || @d || @e || @f || @g || @h
  end
  def init
    @c = @d = @e = @f = @g = @h = nil
  end
end

AI = A.new

BI = B.new

CI = C.new
CI.read
CI.init

Benchmark.ips do |x|
  r = nil
  x.iterations = 2
  x.report('initialized read')   { r = AI.read }
  x.report('uninitialized read') { r = BI.read }
  x.report('init + uninit read') { r = CI.read }
  x.compare!
end

results.txt

$ ruby -v
ruby 2.6.6p146 (2020-03-31 revision 67876) [x86_64-linux]

$ ruby bench_ivar_set2.rb
Warming up --------------------------------------
    initialized read     1.500M i/100ms
  uninitialized read     1.259M i/100ms
  init + uninit read     1.500M i/100ms
    initialized read     1.565M i/100ms
  uninitialized read     1.274M i/100ms
  init + uninit read     1.488M i/100ms
Calculating -------------------------------------
    initialized read     15.292M (± 2.6%) i/s -     76.663M in   5.016528s
  uninitialized read     12.763M (± 2.0%) i/s -     64.995M in   5.094516s
  init + uninit read     14.833M (± 0.5%) i/s -     74.382M in   5.014795s
    initialized read     14.921M (± 2.0%) i/s -     75.098M in   5.035051s
  uninitialized read     12.886M (± 1.1%) i/s -     64.995M in   5.044628s
  init + uninit read     14.989M (± 2.0%) i/s -     75.870M in   5.063616s

Comparison:
  init + uninit read: 14989101.7 i/s
    initialized read: 14921107.5 i/s - same-ish: difference falls within error
  uninitialized read: 12885730.1 i/s - 1.16x  (± 0.00) slower

$ ruby -v
truffleruby 20.3.0-dev-b7a9b466, like ruby 2.6.6, GraalVM CE Native [x86_64-linux]

$ ruby bench_ivar_set2.rb
Warming up --------------------------------------
    initialized read    71.509M i/100ms
  uninitialized read    71.547M i/100ms
  init + uninit read    21.706M i/100ms
    initialized read    71.512M i/100ms
  uninitialized read    71.595M i/100ms
  init + uninit read    21.546M i/100ms
Calculating -------------------------------------
    initialized read    709.399M (± 1.6%) i/s -      3.576B in   5.041755s
  uninitialized read    704.610M (± 0.8%) i/s -      3.580B in   5.080767s
  init + uninit read    212.582M (± 2.2%) i/s -      1.077B in   5.070387s
    initialized read    700.674M (± 0.5%) i/s -      3.504B in   5.001153s
  uninitialized read    704.396M (± 0.3%) i/s -      3.580B in   5.082056s
  init + uninit read    214.761M (± 0.5%) i/s -      1.077B in   5.016355s

Comparison:
  uninitialized read: 704396153.8 i/s
    initialized read: 700673745.0 i/s - same-ish: difference falls within error
  init + uninit read: 214761238.7 i/s - 3.28x  (± 0.00) slower