With Ruby 1.9 the YARV-VM was merged into Ruby. So http://www.atdot.net/yarv seems to be outdated.
Where can I find documentation on RubyVM::InstructionSequence? Especially on #compile_file?
Where can I find an up-to-date Instruction Table like http://www.atdot.net/yarv/insnstbl.html ?
The documentation for that part of YARV is rather poor. I'm not sure whether that is because the only developer who truly understands it doesn't speak English or whether it is deliberate, because that part of YARV still is in heavy development.
Your best bet is to use the source, ask questions on the ruby-core mailinglist or (for best results) learn Japanese and ask questions on the ruby-dev mailinglist.
The thing is, before there is a working bytecode verifier (à la JVM), the developers really don't want you messing about with bytecode too much, because by creating illegal or otherwise "funny" bytecode sequences by hand (i.e. not produced by the YARV compiler itself) you can crash the VM (or worse).