Sketch out nodes.
Compute a Control Flow Graph.
Add a mechanism for dumping a spesh graph.
Install spesh headers.
Start stubbing in dominance computation.
Ensure exception handlers are alive in the CFG.
Eliminate dead BBs, calculate predecessors.
First pass at computing dominance.
Catch infinite intersect; pick processed idom only
Compute dominance frontiers.
Compute assign sets in prep for SSA.
Add overall phi function insertion algorithm.

Doesn't actually add them just yet, just finds where we would.
Implement placement of phi functions.
Flesh out spesh instruction dumping a bit.

Enough to see locals and what SSA number we're giving them, once we
get to that.
Compute dominator tree children.
Do renaming, thus completing SSA computation.
Store indexes in spesh graph; delay resolution.

We need to be able to write these out at code-gen time, so can't just
throw them away.
Fix the way we check for reg read/write.
Add missing memory cleanup.
Fix up instruction offsets to BBs in CFG.