Remove debug print.
Emit a type variable by default in Builder#control_flow_op.
Instrument addition of containing instructions when instrumenting a basic block.
Add type specialization support.
Argument does not have side effects (WTF.)
Terminators only have side effects if they exit.
Don't instrument removed basic blocks.
Implement BasicBlock#prepend.
Implement BasicBlock#splice.
Clear @named_prefixes in Function#initialize_copy.