This class contains code for quick and dirty instruction selection
by forcing each instruction to be a tree and generating the trees in
the same input as the input LIR instructions.
This results in poor code quality, but can be done very quickly.
The intended purpose is to reduce compile time by doing quick and
dirty instruction selection for infrequently executed basic blocks.
Build a BURS Tree for each Instruction.
Complete BURS trees by adding leaf nodes as needed, and
creating tree edges by calling insertChild1() or insertChild2()
This step is also where we introduce intermediate tree nodes for
any LIR instruction that has > 2 "real" operands e.g., a CALL.
s - The instruction for which a tree must be built