[PATCH] [PowerPC] Fix unwind info with dynamic stack realignment

[hfinkel at anl.gov]

Thanks for working on this. I know very little about the CFI directives, and so I'm afraid this might not be the end of the story; specifically, I'm worried about the meaning of the offsets used for the other registers.

When we have a stack pointer or a frame pointer, these store the values of those registers after being adjusted for the local stack size. When we use a base pointer, the base pointer hold the pre-adjusted r1 value. So in PPCRegisterInfo::eliminateFrameIndex we have this:

  if (!MF.getFunction()->getAttributes().
        hasAttribute(AttributeSet::FunctionIndex, Attribute::Naked)) {
    if (!(hasBasePointer(MF) && FrameIndex < 0))
      Offset += MFI->getStackSize();
  }

because to access parent-frame relative objects using the stack/frame pointer we need to add back the local stack size, but if we're using a base pointer, we don't. Maybe this is all fine, but using the same offsets when calling MCCFIInstruction::createOffset for the sp/fp and the bp seems suspicious. Can you please confirm that the offsets are indeed correct in all cases, and regardless, please add some comments explaining your conclusion.

http://reviews.llvm.org/D6410