Check sub register relations in RA

Hi there,

In my register allocator, I was trying to get the parent of a register in ARM.

That is:

D0 <-> S0, S1.

Given S0, how am I able to get D0?

Thanks,
Xiaochu

A register can have multiple super registers/sub registers which you can query with the MCSuperRegIterator/MCSubRegIterator. You may also have register aliases that do not completely overlap a register, you can query those with the MCRegAliasIterator (super/sub registers count as aliases too), however arbitrary aliases are rare in llvm I believe the ARM target for example doesn't use any.

BTW: Most register allocators in llvm work on the register unit level instead of walking the sub/super register hierarchies.

Greetings
    Matthias

Thanks, Matthias! My RA is a legacy one which is ported to LLVM. I will use regunit later for consistency.