Fixed register operations

Hi all,

is it possible to define an instruction as always having a certain register as operand in 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.