[LLVMdev] [PATCH] Handle tied sub-operands in AsmMatcherEmitter

[Ulrich Weigand]

Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote on 24.04.2013 23:47:54:

> I would like to add one more case here: Fixed register operands.
>
> Some instructions, like x86's MUL and DIV, take operands in fixed
> registers. Currently, we handle that with COPY instructions to and
> from the fixed registers, but that is making code motion passes more
> complicated than they need to be. (Actually, they usually just run
> away when they see one of these instructions).
>
> I would like to have MUL32r take two virtual register operands, one
> of them tied to the fixed register %EAX. Just like two-address
> instructions, it would be the register allocator's responsibility to
> satisfy the constraint. This would also make it possible to write
> proper isel patterns for MUL and DIV.

I'm wondering: is is not possible to handle this case by using a
register class containing just the one register?


Bye,
Ulrich