eliminateFrameIndex

Hi!

I started writing a LLVM backend for a custom architecture. I have some register and instruction .td files and some other files/classes like a MCStreamer for assembler output. At the moment I can compile some empty programs so far.

I implemented the method ::eliminateFrameIndex() similar to the Sparc and ARM backend. The method looks like this:

// frame pointer is in reg of class mytarget::ARegsRegClass
unsigned ScratchReg = MF.getRegInfo().createVirtualRegister(&mytarget::ARegsRegClass);
const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
BuildMI(*MI.getParent(), II, dl, TII.get(mytarget::ADD_AReg), ScratchReg).addReg(FramePtr).addImm(Offset);
// Update the original instruction to use the scratch register.
MI.getOperand(FIOperandNum).ChangeToRegister(ScratchReg, false);

But for the test case

int foo(void)
{
  int a = 43;
  return(41);
}

I get the error message "Remaining virtual register operands".

Is something wrong with my method? Did I miss to implement some more methods?

Thanks in advance,
Boris

Hi, you need to override requiresRegisterScavenging()
and requiresFrameIndexScavenging() in your XXXRegisterInfo class to return
true.
FrameIndex elimination is done after RegAlloc and this tells LLVM to use
the RegisterScavenging to get a new register during frame elimination.

Hi!

Hi, you need to override requiresRegisterScavenging() and requiresFrameIndexScavenging() in your XXXRegisterInfo class to return true.
FrameIndex elimination is done after RegAlloc and this tells LLVM to use the RegisterScavenging to get a new register during frame elimination.

Success! Thanks Francois

Boris