RFC: Suggestion for tools for Ruby 1.9 instruction code manipulator?

[r]

Suppose I want to write something that dynamically (i.e. at run-time)
changes VM::InstructionSequences. Maybe I want to write my own JIT
code improver or peephole optimizer, or set a breakpoint by replacing
an instruction with a "trace" instruction.

Are there any tools out there outside of what comes with Ruby?

Some of the things I think would be desired are: accessing individual
instructions, setting individual instructions. Modifying instructions,
replacing one instruction sequence with another. Changing the VM
instruction pointer.

Thanks.