[LLVMdev] Fixed register operations

Jakob Stoklund Olesen stoklund at 2pi.dk
Sun May 16 15:43:45 CDT 2010


On May 16, 2010, at 1:23 PM, Carlos Sánchez de La Lama wrote:
> 
> is it possible to define an instruction as always having a certain  
> register as operand in XXXInstrInfo.td? I know I can do it defining a  
> single-register register class, but I need that register also to be on  
> a broader class for other operations (and it is not possible for a reg  
> to be in several classes AFAIU).

A register can be in multiple register classes, no problem, but we try to avoid single-register classes.

Look at how X86 handles the MUL and DIV instructions. There is some special code in X86DAGToDAGISel::Select as well.

/jakob




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