[LLVMdev] forcing two instructions to be together

[Micah Villmow]

Reed,
 Couldn't you also use instruction scheduling classes and specify that the second instruction has a bypass from the first instruction? The scheduler should always schedule them together in that case.

Micah

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
> Behalf Of reed kotler
> Sent: Tuesday, September 17, 2013 3:59 PM
> To: Owen Anderson
> Cc: llvmdev Mailing List
> Subject: Re: [LLVMdev] forcing two instructions to be together
> 
> On 09/17/2013 03:52 PM, Owen Anderson wrote:
> > +the list again
> > On Sep 17, 2013, at 3:48 PM, reed kotler <rkotler at mips.com> wrote:
> >
> >> On 09/17/2013 03:46 PM, Owen Anderson wrote:
> >>> On Sep 17, 2013, at 3:08 PM, reed kotler <rkotler at mips.com> wrote:
> >>>
> >>>> Is there any way, except for using bundles, to force two instructions to be
> sequentially executed?
> >>> What level of codegen are you working at?  There are various mechanisms
> that can be applied, depending on exactly what the constraints are that you
> need to preserve.
> >>>
> >>> -Owen
> >> I have two machine instructions that I need to be together.
> >>
> >>   BuildMI(MBB, I, DL, TII.get(Mips::LiRxImmAlignX16), V0)
> >>     .addExternalSymbol("_gp_disp", MipsII::MO_ABS_HI);
> >>   BuildMI(MBB, I, DL, TII.get(Mips::AddiuRxPcImmX16), V1)
> >>     .addExternalSymbol("_gp_disp", MipsII::MO_ABS_LO);
> >>
> >> It's in Mips16ISelDagToDag.cpp
> >>
> >> these two have to be together because they are both part of a complex pc
> relative calculation.
> >>
> >> I have not used bundles yet and was just looking for an easy way to join
> these two.
> > Bundles is one way you can go.  Another is to use a pseudo instruction that is
> broken up immediately before (or during!) MC emission.
> >
> > -Owen
> I just tried this but something is wrong here. Well, I have not used bundles at
> all.
> I just know how they work conceptually. This compiled okay but I got some
> constraint errors.
> 
>    MIBundleBuilder(MBB, I)
>      .append(BuildMI(MF, DL, TII.get(Mips::LiRxImmAlignX16), V0)
>          .addExternalSymbol("_gp_disp", MipsII::MO_ABS_HI))
>      .append(BuildMI(MF, DL, TII.get(Mips::AddiuRxPcImmX16), V1)
>          .addExternalSymbol("_gp_disp", MipsII::MO_ABS_LO));
> 
> 
> 
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