[llvm-dev] Problem of getting two unused registers in eliminateFrameIndex()

[Ehsan Ali via llvm-dev]

Hello all,

For my custom processor backend I am trying add some instruction using
BuildMI() inside eliminateFrameIndex().

I tried RegScavenger like this:

unsigned RegUnused0 = RS->FindUnusedReg(&LASER::GNPRegsRegClass);
if (!RegUnused0)
  RegUnused0 = RS->scavengeRegister(&LASER::GNPRegsRegClass, II, SPAdj);
assert(RegUnused0 && "Register scavenger failed");
RS->setRegUsed(RegUnused0);

It works but there are two issues:

1) I need to registers and RegScavenger only returns one.
2) I cannot unset the used register and I get spill slot error message
when I ran out of the available registers.

So I gave up and tried createVirtualRegister():

MachineRegisterInfo &RegInfo = MBB.getParent()->getRegInfo();
const TargetRegisterClass *RC = &LASER::GNPRegsRegClass;
unsigned Reg = RegInfo.createVirtualRegister(RC);

But then I get the following error:

MachineCopyPropagation.cpp:267: void
anonymous}::MachineCopyPropagation::CopyPropagateBlock(llvm::MachineBasicBlock&):
Assertion `!TargetRegisterInfo::isVirtualRegister(Reg) &&
"MachineCopyPropagation should be run after register allocation!"'
failed.

How can I solve my problem of getting two free registers in
eliminateFrameIndex() ?

Thank you,
Ehsan Ali.