[LLVMdev] Subregister definition / use

[Jakob Stoklund Olesen]

On Nov 9, 2011, at 7:48 AM, Jonas Paulsson wrote:

> Hi,
> 
> I can't find a way to define a subregister in a MI, while using another subregister in the same MI.
> 
> For example:
> 
> reg:low  = OP reg:hi, rhs
> 
> I really need the reg:low to be part of the same register as reg:hi

LLVM doesn't support this kind of constraint in its default register allocators.

You may be able to get the PBQP allocator to enforce the constraint.

Alternatively, model your instruction as reading and writing the full register with a normal two-addr constraint.

/jakob

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