Chris Lattner wrote:
>
> Why can't you just mark the frame address callee save? Why isn't it
> getting saved automatically for you?
>
Because R31 is not used as a callee saved register when
llvm::NoFramePointerElim is set to 1. The algorithm
that calculates the callee saved registers' addresses does not save
R31's offset when used as a frame pointer.
And with the ELF Abi, R31's offset is in the callee saved registers
area. Therefore I have to force its allocation
(at the -4 offset).
> Index: PPCRegisterInfo.cpp
> ===================================================================
> RCS file: /var/cvs/llvm/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp,v
> retrieving revision 1.114
> diff -t -d -u -p -5 -r1.114 PPCRegisterInfo.cpp
> --- PPCRegisterInfo.cpp 27 Feb 2007 11:55:45 -0000 1.114
> +++ PPCRegisterInfo.cpp 27 Feb 2007 17:29:51 -0000
> @@ -879,10 +879,30 @@ void PPCRegisterInfo::processFunctionBef
> // Save and clear the LR state.
> PPCFunctionInfo *FI = MF.getInfo<PPCFunctionInfo>();
> unsigned LR = getRARegister();
> FI->setUsesLR(MF.isPhysRegUsed(LR));
> MF.changePhyRegUsed(LR, false);
> +
> +
> + // Save R31 if necessary
> + int FPSI = FI->getFramePointerSaveIndex();
> + bool IsPPC64 = Subtarget.isPPC64();
> + bool IsMachoABI = Subtarget.isMachoABI();
> + const MachineFrameInfo *MFI = MF.getFrameInfo();
> + + // If the frame pointer save index hasn't been defined yet.
> + if (!FPSI && (NoFramePointerElim || MFI->hasVarSizedObjects())
> + && !IsMachoABI) {
> + // Find out what the fix offset of the frame pointer save area.
> + int FPOffset = PPCFrameInfo::getFramePointerSaveOffset(IsPPC64,
> +
> IsMachoABI);
> + // Allocate the frame index for frame pointer save area.
> + FPSI = MF.getFrameInfo()->CreateFixedObject(IsPPC64? 8 : 4,
> FPOffset);
> + // Save the result.
> + FI->setFramePointerSaveIndex(FPSI); + }
> +
> }
>
>
>
> void PPCRegisterInfo::emitPrologue(MachineFunction &MF) const {
> MachineBasicBlock &MBB = MF.front(); // Prolog goes in entry BB
> MachineBasicBlock::iterator MBBI = MBB.begin();
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