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

[Hal Finkel via llvm-dev]

----- Original Message -----
> From: "Xiaochu Liu" <xiaochu1122 at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "LLVM Developers Mailing List" <llvm-dev at lists.llvm.org>
> Sent: Tuesday, November 24, 2015 5:35:36 PM
> Subject: Re: [llvm-dev] [backend]two-address encoding in llvm tblgen
> 
> 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)?

Yes, you'll need to add all three operands. Note that before register allocations (specifically, when the MIs are still in SSA form), they'll have different virtual registers.

 -Hal

> 
> 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
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
> >
> > --
> > Hal Finkel
> > Assistant Computational Scientist
> > Leadership Computing Facility
> > Argonne National Laboratory
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory