Blocks are one of the most expressive parts of the Ruby syntax. Many Ruby methods take a block. When a method is given different blocks, there is a crucial optimization necessary to unlock the best performance. This optimization dates back to the early days of research on dynamic languages, yet it seems only a single Ruby implementation currently uses it. This optimization is called splitting and what it does is using different copies of a method and specialize them to the block given at different call sites. This enables compiling the method and the block together for the best performance.
Benoit Daloze is the TruffleRuby lead. He has contributed to many Ruby implementations, including MRI, TruffleRuby and JRuby. He is the maintainer of ruby/spec, a test suite for the behavior of the Ruby programming language.