emit vs. visit in LIR interface

[Deneau, Tom]

Say you've defined a new XxxNode and a LoweredXxxNode version also.
In the generate method for the LoweredXxxNode, what determines whether one should

a)      define a emitXxx in the LIRGenerator interface, do the parsing work in the LoweredXxxNode.generate method itself, and then call gen.emitXXX (like for example the say BitCountNode.generate works)

b)      define a visitXxx routine as part of the LIRGenerator interface, and the LoweredXxxNode.generate  basically just calls gen.visitXxx(LoweredXxxNode) and do the real work in the visitXxx (like for example VisitCompareAndSwap)

-- Tom