[llvm-dev] Check sub register relations in RA

[Matthias Braun via llvm-dev]

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

> On Jul 19, 2016, at 10:42 AM, Xiaochu Liu via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> 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
> 
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