[LLVMdev] Post-RA Def/Use Information

[dag at cray.com]

Owen Anderson <resistor at mac.com> writes:

> Right, the code is no longer in SSA form at this point.  If we want to
> get SSA information at this level, I suspect you want to be querying
> LiveIntervals, which has that information, assuming it's still live.

LiveIntervals is better than nothing but it's still more expensive than
querying def/use chains.  I don't know where the crossover point is,
where calculating def/use chains would be less expensive than repeated
iterations over MachineInstr register def/use lists and queries of
LiveIntervals.

Still, it should allow me to do the safety analysis.  This will run
immediately after RA so hopefully LiveIntervals is still, uh, live.  :)

It should be good enough for now.  Thanks!

                              -Dave