Bench for https://github.com/rubocop-hq/rubocop/pull/8986

getter_lvar.rb

require 'benchmark'

class X
  attr_accessor :foo

  def getter
    foo + foo
  end

  def lvar
    _foo = foo
    _foo + _foo
  end
end

x = X.new
x.foo = 1

n = 100_000_000

Benchmark.bmbm do |r|
  r.report('getter') { n.times { x.getter } }
  r.report('lvar') { n.times { x.lvar } }
end

# Rehearsal ------------------------------------------
# getter   6.287069   0.024509   6.311578 (  6.347462)
# lvar     6.234191   0.025029   6.259220 (  6.295198)
# -------------------------------- total: 12.570798sec

#              user     system      total        real
# getter   6.284312   0.024804   6.309116 (  6.346137)
# lvar     6.168816   0.024180   6.192996 (  6.228303)
# 
# > ruby -v                                                                                                                                                                                                                    ~/src
# ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin19]