[llvm-dev] Reg units for unaddressable register parts?

Quentin Colombet via llvm-dev llvm-dev at lists.llvm.org
Wed Sep 28 11:20:14 PDT 2016

> On Sep 28, 2016, at 10:52 AM, Krzysztof Parzyszek via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> On X86, the registers AX, EAX and RAX all share the exact same register units. In terms of units, there is no difference between these registers. This makes register units insufficient to track liveness, since live AX does not imply live EAX.

That is exactly the intent.
If AX is live, you don’t want another value to use EAX or RAX.

> Would it make sense to have register units (and lane masks) for the parts of registers that are not individually addressable?
> -Krzysztof
> -- 
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