When matching an incompatible encoding, the Regexp needs to recompile. If `usecnt == 0`, then we can reuse the `ptr` because nothing else is using it. This avoids allocating another `regex_t`. This speeds up matches that switch to incompatible encodings by 15%. Branch: ``` Regex#match? with different encoding 1.431M (± 1.3%) i/s - 7.264M in 5.076153s Regex#match? with same encoding 16.858M (± 1.1%) i/s - 85.347M in 5.063279s ``` Base: ``` Regex#match? with different encoding 1.248M (± 2.0%) i/s - 6.342M in 5.083151s Regex#match? with same encoding 16.377M (± 1.1%) i/s - 82.519M in 5.039504s ``` Script: ``` regex = /foo/ str1 = "日本語" str2 = "English".force_encoding("ASCII-8BIT") Benchmark.ips do |x| x.report("Regex#match? with different encoding") do |times| i = 0 while i < times regex.match?(str1) regex.match?(str2) i += 1 end end x.report("Regex#match? with same encoding") do |times| i = 0 while i < times regex.match?(str1) i += 1 end end end ```