llvm dev - Sep 2008 - [LLVMdev] A question about instruction operands.

I have a question:
In the pattern below from X86

def INC8r  : I<0xFE, MRM0r, (outs GR8 :$dst), (ins GR8 :$src),
			"inc{b}\tdst",
		  [(set GR8:$dst, (add GR8:$src, 1))]>;

Since we are emitting only "inc $dst",
What makes sure that the $src and $dst are same register?

- Sanjiv

sanjiv gupta wrote:
> I have a question:
> In the pattern below from X86
>
> def INC8r  : I<0xFE, MRM0r, (outs GR8 :$dst), (ins GR8 :$src),
> 			"inc{b}\tdst",
> 		  [(set GR8:$dst, (add GR8:$src, 1))]>;
>
> Since we are emitting only "inc $dst",
> What makes sure that the $src and $dst are same register?
>
> - Sanjiv
It's enclosed inside :

let isTwoAddress = 1 in {
...
}

(you'll need to scroll up a fair amount to find this).

Richard

On Tue, 2008-09-23 at 13:33 +0100, Richard Osborne
wrote:
> sanjiv gupta wrote:
> > I have a question:
> > In the pattern below from X86
> >
> > def INC8r  : I<0xFE, MRM0r, (outs GR8 :$dst), (ins GR8 :$src),
> > 			"inc{b}\tdst",
> > 		  [(set GR8:$dst, (add GR8:$src, 1))]>;
> >
> > Since we are emitting only "inc $dst",
> > What makes sure that the $src and $dst are same register?
> >
> > - Sanjiv
> It's enclosed inside :
> 
> let isTwoAddress = 1 in {
> ...
> }
> 
> (you'll need to scroll up a fair amount to find this).
> 
That means, it gets converted to
dst = src;
dst = dst + 1;

Right ?

- Sanjiv
> Richard
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

BTW, please use the operand constraint syntax instead of the  
deprecated isTwoAddress syntax:

let Constraints = "$src1 = $dst" in

Evan

On Sep 23, 2008, at 5:33 AM, Richard Osborne wrote:
> sanjiv gupta wrote:
>> I have a question:
>> In the pattern below from X86
>>
>> def INC8r  : I<0xFE, MRM0r, (outs GR8 :$dst), (ins GR8 :$src),
>> 			"inc{b}\tdst",
>> 		  [(set GR8:$dst, (add GR8:$src, 1))]>;
>>
>> Since we are emitting only "inc $dst",
>> What makes sure that the $src and $dst are same register?
>>
>> - Sanjiv
> It's enclosed inside :
>
> let isTwoAddress = 1 in {
> ...
> }
>
> (you'll need to scroll up a fair amount to find this).
>
> Richard
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev