perf: use -O2 to compile libgumbo and the nokogiri extension

[flavorjones]

What problem is this PR intended to solve?

My benchmarks show this generates code that is:

• 22% faster at HTML5 serialization
• 93% faster at HTML5 parsing

Note that -O3 generates slightly slower HTML5 serialization
code (see 8220dc7).

Note also that this doesn't change the compiler options used for
libxml2 and libxslt (which includes -O2 already).

Using the following benchmark script:

#! /usr/bin/env ruby
# coding: utf-8

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "nokogiri", path: "."
  gem "benchmark-ips"
end

require "nokogiri"
require "benchmark/ips"

input = File.read("test/files/tlm.html")
puts "input #{input.length} bytes"

html4_doc = Nokogiri::HTML4::Document.parse(input)
html5_doc = Nokogiri::HTML5::Document.parse(input)

puts RUBY_DESCRIPTION

Benchmark.ips do |x|
  x.time = 10
  x.report("html5 parse") do
    Nokogiri::HTML5::Document.parse(input)
  end
  x.report("html4 parse") do
    Nokogiri::HTML4::Document.parse(input)
  end
  x.compare!
end

Benchmark.ips do |x|
  x.time = 10
  x.report("html5 serialize") do
    html5_doc.to_html
  end
  x.report("html4 serialize") do
    html4_doc.to_html
  end
  x.compare!
end

with default settings on my dev system
(which are -O3 for extension and unspecified for libgumbo):

input 70095 bytes
ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]
Warming up --------------------------------------
html5 parse 12.000 i/100ms
html4 parse 31.000 i/100ms
Calculating -------------------------------------
html5 parse 129.637 (±16.2%) i/s - 1.260k in 10.051475s
html4 parse 355.723 (±21.4%) i/s - 3.441k in 10.104502s

Comparison:
html4 parse: 355.7 i/s
html5 parse: 129.6 i/s - 2.74x (± 0.00) slower

Warming up --------------------------------------
html5 serialize 85.000 i/100ms
html4 serialize 131.000 i/100ms
Calculating -------------------------------------
html5 serialize 843.993 (± 2.4%) i/s - 8.500k in 10.076902s
html4 serialize 1.319k (± 2.9%) i/s - 13.231k in 10.039827s

Comparison:
html4 serialize: 1319.0 i/s
html5 serialize: 844.0 i/s - 1.56x (± 0.00) slower

after enabling -O2 on both gumbo and nokogiri source files:

input 70095 bytes
ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]
Warming up --------------------------------------
html5 parse 21.000 i/100ms
html4 parse 36.000 i/100ms
Calculating -------------------------------------
html5 parse 250.245 (±20.8%) i/s - 2.394k in 10.066381s
html4 parse 371.905 (±20.2%) i/s - 3.600k in 10.025980s

Comparison:
html4 parse: 371.9 i/s
html5 parse: 250.2 i/s - same-ish: difference falls within error

Warming up --------------------------------------
html5 serialize 101.000 i/100ms
html4 serialize 128.000 i/100ms
Calculating -------------------------------------
html5 serialize 1.037k (± 3.3%) i/s - 10.403k in 10.042146s
html4 serialize 1.301k (± 4.2%) i/s - 13.056k in 10.055585s

Comparison:
html4 serialize: 1300.8 i/s
html5 serialize: 1037.2 i/s - 1.25x (± 0.00) slower

[stevecheckoway]

LGTM

I'm a little surprised we weren't already using -O2 or -O3.

[flavorjones]

@stevecheckoway Yeah, this was a rather obvious (in hindsight) missed opportunity.

[choosen]

@flavorjones Can it be backported to 1.13.x ?

for ruby 2.6.x ?

[flavorjones]

@choosen No, sorry, I won't be backporting this change. Patch releases are intended for security and bug fixes, please see the section in the README on our interpretation of semantic versioning.