[llvm-commits] llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp

[Nicolas Geoffray]

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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