dominator tree

[mnikander]

• dominator tree computed once for each program (during or prior to execution)
• use dominator tree to search for register names in predecessor blocks, and their predecessors
• unit test passes for phi node which merges a register from 'grandparent' block

[mnikander]

• Optionally: add a dictionary which keeps track of which register comes from which block, to make it easier to find the register values when evaluating phi nodes

[mnikander]

The phi node specifies the corresponding predecessor nodes explicitly, and the 'grandparent' unit test passes, so no extra work is needed for the phi nodes