[llvm-dev] [backend]two-address encoding in llvm tblgen

[Xiaochu Liu via llvm-dev]

Hi Hal,

Thanks for your reply and it is helpful!

I have a quick question:
When I use BuildMI to build instructions in this case, do I have to
add all three of the register operands explicitly (operand 0 and 1 are
the same)?

Thanks,
Xiaochu


On Tue, Nov 24, 2015 at 3:14 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> ----- Original Message -----
>> From: "Xiaochu Liu via llvm-dev" <llvm-dev at lists.llvm.org>
>> To: "LLVM Developers Mailing List" <llvm-dev at lists.llvm.org>
>> Sent: Tuesday, November 24, 2015 5:08:49 PM
>> Subject: [llvm-dev] [backend]two-address encoding in llvm tblgen
>>
>> Dear there,
>>
>> I'm developing an instruction layout like:
>>
>> opcode | rd| ts
>>
>> and its semantics is:
>>
>> rd= rd opcode rs
>>
>> But when I describe it in td file like this:
>>
>> class R<bits<5> Op, string OpcodeStr, list<dag> Pattern>
>> : InstV<(outs GPR:$rd), (ins GPR:$rd, GPR:$rs), !strconcat(OpcodeStr,
>> "\t$rd, $rs"), Pattern> {
>>   bits<5> rd;
>>   bits<6> rs;
>>   let Opcode=Op;
>> }
>
> You need to use a different input and output register, and then tie them together:
>
> class R<bits<5> Op, string OpcodeStr, list<dag> Pattern>
> : InstV<(outs GPR:$rd), (ins GPR:$rdi, GPR:$rs), !strconcat(OpcodeStr,
> "\t$rd, $rs"), Pattern> {
>   bits<5> rd;
>   bits<6> rs;
>   let Opcode=Op;
>
>   let Constraints = "$rdi = $rd";
>   let DisableEncoding = "$rdi";
> }
>
>  -Hal
>
>>
>> It complains for 'rd'. I was wondering if there is any standard way
>> of
>> doing this?
>>
>> Thanks,
>> Xiaochu
>> _______________________________________________
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>> llvm-dev at lists.llvm.org
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>>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory