Compatibility is one, it's hard to be 100% compatible with CRuby, and large codebases tend to sometimes depend unintentionally on weird behavior or even bugs in

Compatibility is one, it's hard to be 100% compatible with CRuby, and large codebases tend to sometimes depend unintentionally on weird behavior or even bugs in CRuby. Keeping up compatibility (while keeping things efficient) is a lot of work, TruffleRuby tries to reduce that by reusing as much as possible existing code, including reusing C extensions shipped with CRuby.