_partial.haml

%foo
  %bar= i

application_helper.rb

module ApplicationHelper
  def tag_helper(i)
    content_tag(:foo) {
      content_tag(:bar, i)
    }
  end

  def haml_naive(i)
    Haml::Engine.new(<<~HAML).render(Object.new, i: i).html_safe
      %foo
        %bar= i
    HAML
  end

  Haml::Engine.new(<<~HAML).def_method self, :haml_precompiled, :i
    %foo
      %bar= i
  HAML
end

log.txt

$ bin/rails s -e production
=> Booting Puma
=> Rails 5.0.0.1 application starting in production on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.6.0 (ruby 2.3.1-p112), codename: Sleepy Sunday Serenity
* Min threads: 5, max threads: 5
* Environment: production
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
                       user     system      total        real
partial            0.150000   0.020000   0.170000 (  0.168522)
tag_helper         0.060000   0.000000   0.060000 (  0.065240)
haml_naive         0.530000   0.000000   0.530000 (  0.528725)
haml_precompiled   0.030000   0.000000   0.030000 (  0.026623)
                       user     system      total        real
partial            0.170000   0.010000   0.180000 (  0.213928)
tag_helper         0.060000   0.010000   0.070000 (  0.060891)
haml_naive         0.430000   0.000000   0.430000 (  0.438646)
haml_precompiled   0.010000   0.000000   0.010000 (  0.013547)
                       user     system      total        real
partial            0.150000   0.010000   0.160000 (  0.157855)
tag_helper         0.070000   0.010000   0.080000 (  0.074357)
haml_naive         0.460000   0.000000   0.460000 (  0.470439)
haml_precompiled   0.010000   0.000000   0.010000 (  0.010962)

show.haml

- Benchmark.bm 16 do |x|
  - x.report 'partial' do
    - 1000.times do |i|
      = render 'partial', i: i

  - x.report 'tag_helper' do
    - 1000.times do |i|
      = tag_helper i

  - x.report 'haml_naive' do
    - 1000.times do |i|
      = haml_naive i

  - x.report 'haml_precompiled' do
    - 1000.times do |i|
      = haml_precompiled i: i