Run the verify_contexti() function after invoking the legalize() and
regalloc() context functions. This will help catch bad code produced by
these passes.
Legalizing some instructions may require modifications to the control
flow graph, and some operations need to use the CFG analysis.
The CFG reference is threaded through all the legalization functions to
reach the generated expansion functions as well as the legalizer::split
module where it will be used first.
