llvm dev - Nov 2021 - LiveRegUnits vs LivePhysRegs

Why do we have both  LiveRegUnits and LivePhysRegs? They seem to do
the same job of tracking physical register liveness at RegUnit
granularity. The only difference I have noticed is that LivePhysRegs
provides both stepForward and stepBackward, but LiveRegUnits only has
stepBackward.

Thanks,
Jay.

Take it with a grain of salt, Matthias may remember better, but I think that’s
just an historical quirk that some client didn’t want to deal with with regunit.
> On Nov 2, 2021, at 4:51 AM, Jay Foad via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Why do we have both  LiveRegUnits and LivePhysRegs? They seem to do
> the same job of tracking physical register liveness at RegUnit
> granularity. The only difference I have noticed is that LivePhysRegs
> provides both stepForward and stepBackward, but LiveRegUnits only has
> stepBackward.
> 
> Thanks,
> Jay.
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