llvm dev - May 2013 - [LLVMdev] MachineOperand Fixed Register

Is there any way to determine if a Register-type MachineOperand
represents a fixed machine register?  For example, call arguments must
end up in specific machine register but I don't see any way to ascertain
this from the information in MachineOperand.  Basically, I need to know
if I am allowed to rename a MachineOperand or not after register
allocation.

Thanks!

                           -David

On May 16, 2013, at 2:23 PM, dag at cray.com wrote:
> Is there any way to determine if a Register-type MachineOperand
> represents a fixed machine register?  For example, call arguments must
> end up in specific machine register but I don't see any way to
ascertain
> this from the information in MachineOperand.  Basically, I need to know
> if I am allowed to rename a MachineOperand or not after register
> allocation.
I think the anti-dependency breakers in the post-RA scheduler can do that.

/jakob

Jakob Stoklund Olesen <stoklund at 2pi.dk> writes:
> On May 16, 2013, at 2:23 PM, dag at cray.com wrote:
>
>> Is there any way to determine if a Register-type MachineOperand
>> represents a fixed machine register?  For example, call arguments must
>> end up in specific machine register but I don't see any way to
ascertain
>> this from the information in MachineOperand.  Basically, I need to know
>> if I am allowed to rename a MachineOperand or not after register
>> allocation.
>
> I think the anti-dependency breakers in the post-RA scheduler can do that.
Ok, will take a look, thanks!

I think I've cobbled something together that works by not allowing
manipulation of call operands, implicit defs/uses (which could be
"wired" registers) and any operand of
"hasExtraSrcRegAllocReq()"
instructions.  Seems to cover it for now, anyway, though it may be too
restrictive.

                        -David