Major slowdown in String#gsub and String#gsub! (UTF-8 input with ASCII replacement) after commit f4fd34a.

bench.rb

Benchmark.ips do |x|
  str1 = "YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh\n" * 6000
  repl1 = "\r\n"

  x.report 'gsub ASCII with ASCII' do
    str1.gsub(/\n|\r\n|\r/){ repl1 }
  end

  str2 = "YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh\n" * 6000
  str2.encode! 'utf-8'
  repl2 = "\r\n"

  x.report 'gsub UTF-8 with ASCII' do
    str2.gsub(/\n|\r\n|\r/){ repl2 }
  end

  str3 = "YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh\n" * 6000
  str3.encode! 'utf-8'
  repl3 = "\r\n"
  repl3.encode! 'utf-8'

  x.report 'gsub UTF-8 with UTF-8' do
    str3.gsub(/\n|\r\n|\r/){ repl3 }
  end
end

gistfile1.txt

.

rbx-215cc7ac

rubinius 2.0.0.rc1 (1.9.3 215cc7ac yyyy-mm-dd JI) [x86_64-unknown-linux-gnu]

=== /usr/local/rubinius/2.0/bin/rbx ===
gsub ASCII with ASCII
                           79.8 (±12.5%) i/s -        390 in   5.001304s (cycle=5)
gsub UTF-8 with ASCII
                            1.1 (±0.0%) i/s -          6 in   5.347251s (cycle=1)
gsub UTF-8 with UTF-8
                           54.4 (±5.5%) i/s -        272 in   5.021096s (cycle=4)

rbx-b89c065b

rubinius 2.0.0rc1 (1.9.3 b89c065b 2012-11-02 JI) [x86_64-unknown-linux-gnu]

=== bin/rbx ===
gsub ASCII with ASCII
                           55.1 (±14.5%) i/s -        275 in   5.102085s (cycle=5)
gsub UTF-8 with ASCII
                           40.3 (±14.9%) i/s -        198 in   5.011385s (cycle=3)
gsub UTF-8 with UTF-8
                           40.0 (±12.5%) i/s -        198 in   5.030680s (cycle=3)