Invalid base register with fast-isel

[Ulrich Weigand]

Hal Finkel <hfinkel at anl.gov> wrote on 27.06.2014 13:07:32:

> > As far as I can see, that latter process took place long after
> > FastISel, and with FastISel having no oppportunity to influence
> > its choices ...
> >
> > Am I missing something here?
>
> You're right; but logically, the restriction does not belong on the
> output from materializeFrameBaseRegister. Can you constrain the
> register class on the store operand near the end of
> PPCRegisterInfo::eliminateFrameIndex?

Hmm, those instructions were not touched by eliminateFrameIndex
either :-)

LocalStackSlotPass::insertFrameReferenceRegisters allocates the
base register here:
      BaseReg = Fn.getRegInfo().createVirtualRegister(RC);

It then calls:
      // Tell the target to insert the instruction to initialize
      // the base register.
      //            MachineBasicBlock::iterator InsertionPt = Entry->begin
();
      TRI->materializeFrameBaseRegister(Entry, BaseReg, FrameIdx,
                                        InstrOffset);

and finally:
    // Modify the instruction to use the new base register rather
    // than the frame index operand.
    TRI->resolveFrameIndex(*I, BaseReg, Offset);

So I guess the only chance to constrain the register are either
materializeFrameBaseRegister or else resolveFrameIndex.  Did you
mean to refer to the latter?


Bye,
Ulrich