Improve Node#each_recursive performance (#139)

Fix #134

## Summary

This PR does:

- Add `benchmark/each_recursive.yaml`
- Rewrite `Node#each_recursive` implementation for performance
- Add a test for `Node#each_recursive`

The performance of `Node#each_recursive` is improved 60~80x faster.

## Details

`each_recursive` is too much slow as I described in #134.
I improved this performance by rewriting its implementation in this PR.

Also, I added a benchmark in `benchmark/each_recursive.yaml` and the
following is a result on my laptop:

```
RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/makenowjust/Projects/github.com/makenowjust/simple-dotfiles/.asdf/installs/ruby/3.3.2/bin/ruby -v -S benchmark-driver /Users/makenowjust/Projects/github.com/ruby/rexml/benchmark/each_recursive.yaml
ruby 3.3.2 (2024-05-30 revision e5a195edf6) [arm64-darwin23]
Calculating -------------------------------------
                     rexml 3.2.6      master  3.2.6(YJIT)  master(YJIT)
      each_recursive      11.279     686.502       17.926        1.470k i/s -     100.000 times in 8.866303s 0.145666s 5.578360s 0.068018s

Comparison:
                   each_recursive
        master(YJIT):      1470.2 i/s
              master:       686.5 i/s - 2.14x  slower
         3.2.6(YJIT):        17.9 i/s - 82.01x  slower
         rexml 3.2.6:        11.3 i/s - 130.35x  slower

```

We can see that the performance is improved 60~80x faster.

Additionally, I added a new test for `Node#each_recursive`.
It was missing, but we need it to confirm not to break the previous
behavior.

Thank you.

---------

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

benchmark/each_recursive.yaml

@@ -0,0 +1,40 @@
+loop_count: 100
+contexts:
+ - gems:
+ rexml: 3.2.6
+ require: false
+ prelude: require 'rexml'
+ - name: master
+ prelude: |
+ $LOAD_PATH.unshift(File.expand_path("lib"))
+ require 'rexml'
+ - name: 3.2.6(YJIT)
+ gems:
+ rexml: 3.2.6
+ require: false
+ prelude: |
+ require 'rexml'
+ RubyVM::YJIT.enable
+ - name: master(YJIT)
+ prelude: |
+ $LOAD_PATH.unshift(File.expand_path("lib"))
+ require 'rexml'
+ RubyVM::YJIT.enable
+
+prelude: |
+ require 'rexml/document'
+
+ xml_source = +"<root>"
+ 100.times do
+ x_node_source = ""
+ 100.times do
+ x_node_source = "<x>#{x_node_source}</x>"
+ end
+ xml_source << x_node_source
+ end
+ xml_source << "</root>"
+
+ document = REXML::Document.new(xml_source)
+
+benchmark:
+ each_recursive: document.each_recursive { |_| }

lib/rexml/node.rb

@@ -52,10 +52,14 @@ def parent?
 
  # Visit all subnodes of +self+ recursively
  def each_recursive(&block) # :yields: node
- self.elements.each {|node|
- block.call(node)
- node.each_recursive(&block)
- }
+ stack = []
+ each { |child| stack.unshift child if child.node_type == :element }
+ until stack.empty?
+ child = stack.pop
+ yield child
+ n = stack.size
+ child.each { |grandchild| stack.insert n, grandchild if grandchild.node_type == :element }
+ end
  end
 
  # Find (and return) first subnode (recursively) for which the block

test/test_document.rb

@@ -209,6 +209,42 @@ def test_gt_linear_performance_attribute_value
  end
  end
 
+ def test_each_recursive
+ xml_source = <<~XML
+ <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+ <root name="root">
+ <x name="1_1">
+ <x name="1_2">
+ <x name="1_3" />
+ </x>
+ </x>
+ <x name="2_1">
+ <x name="2_2">
+ <x name="2_3" />
+ </x>
+ </x>
+ <!-- comment -->
+ <![CDATA[ cdata ]]>
+ </root>
+ XML
+
+ expected_names = %w[
+ root
+ 1_1 1_2 1_3
+ 2_1 2_2 2_3
+ ]
+
+ document = REXML::Document.new(xml_source)
+
+ # Node#each_recursive iterates elements only.
+ # This does not iterate XML declerations, comments, attributes, CDATA sections, etc.
+ actual_names = []
+ document.each_recursive do |element|
+ actual_names << element.attributes["name"]
+ end
+ assert_equal(expected_names, actual_names)
+ end
+
  class WriteTest < Test::Unit::TestCase
  def setup
  @document = REXML::Document.new(<<-EOX)