from the SD / SelectionDAG form of a global-virt-reg, IE a CopyToReg or CopyFromReg
where the Reg is a virtual-register (not a physical-register),
I need to compute the set of all other global-virt-regs that this one is connected
to through PHI nodes
as the PHI nodes set up equivalence relations,
I should be able to use ADT/EquivalenceClasses.h
which seems to implement a generic Union-Find algorithm,
I also note that there do not seem to be any uses of EquivalenceClasses
in CodeGen, so perhaps no one has had to do this before and I will
have to start from scratch ?
thanks,
–Peter Lawrence.