This speeds up setting the backref match object by avoiding some memcopies. Take the following code for example: ```ruby "hello world" =~ /hello/ p $~ ``` When the RE matches the string, we have to set the Match object in the backref global. So we would allocate a match object[^1] and use `rb_reg_region_copy`[^2] to make a deep copy of the stack allocated `re_registers` struct[^3] in to the newly created Ruby object. This could possibly trigger GC[^4], and would allocate new memory. This makes a shallow copy of the `re_registers` struct on to the Match object allowing the match object to manage the `re_registers` pointer and also avoiding some calls to `xmalloc` and some manual memcopy. Benchmark looks like this: ```ruby require "benchmark/ips" def test_re thing thing =~ /hello/ end Benchmark.ips do |x| x.report("re hit") do test_re "hello world" end x.report("re miss") do test_re "world" end end ``` Before this : ``` $ ruby -v test.rb ruby 3.2.0dev (2022-07-27T22:29:00Z master 4ad69899b7) [arm64-darwin21] Ignoring bcrypt-3.1.16 because its extensions are not built. Try: gem pristine bcrypt --version 3.1.16 Warming up -------------------------------------- re hit 345.401k i/100ms re miss 673.584k i/100ms Calculating ------------------------------------- re hit 3.452M (± 0.5%) i/s - 17.270M in 5.002535s re miss 6.736M (± 0.4%) i/s - 34.353M in 5.099593s ``` After this : ``` $ ./ruby -v test.rb ruby 3.2.0dev (2022-08-01T21:24:12Z less-memcpy 0ff2a56606) [arm64-darwin21] Warming up -------------------------------------- re hit 419.578k i/100ms re miss 673.251k i/100ms Calculating ------------------------------------- re hit 4.201M (± 0.7%) i/s - 21.398M in 5.093593s re miss 6.716M (± 0.4%) i/s - 33.663M in 5.012756s ``` Matches get faster and misses maintain the same speed [^1]: https://.com/ruby/ruby/blob/24204d54ab730791bfbd0cd66b8e12f0bd62ca5d/re.c#L1737 [^2]: https://.com/ruby/ruby/blob/24204d54ab730791bfbd0cd66b8e12f0bd62ca5d/re.c#L1738 [^3]: https://.com/ruby/ruby/blob/24204d54ab730791bfbd0cd66b8e12f0bd62ca5d/re.c#L1686 [^4]: https://.com/ruby/ruby/blob/24204d54ab730791bfbd0cd66b8e12f0bd62ca5d/re.c#L981