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

[Chris Lattner]

>>>> In this case, it seems like a clearly good thing to just call
>>>> CreateFixedObject unconditionally early on (e.g.) when lowering the
>>>> arguments.
>>>>
>>>
>>> Unconditionally? I can do that, but do you mean without any check  
>>> if R31
>>> is actually used as frame pointer or we're compiling for linux/ppc?
>>
>> Sorry, I meant "without a check for r31", it should still only  
>> happen on linux/ppc.
>>
>
> Actually why would you like to do this when lowering the arguments?  
> It's possible that
> R31 is never used in the function and calling CreateFixedObject  
> unconditionnaly
> will make the stack reservation for the function at least of 4  
> bytes, right? even if it doesn't
> need to.
>
> Both implementation work, but due to my small knowledge of what's  
> going on in llvm :), I would
> like to follow your idea, but I don't undestand why it's better  
> during arguments lowering than before callee-saved
> register scanning.

I don't understand all the constraints :).  My assumption was that  
the stack slot was actually in the "caller" area, not in the current  
function area.  If it's in the caller area, there is no problem  
creating the stack slot (no space is required).  If it's in the  
callee area, creating the slot will unconditionally force stack to be  
allocated, which *is* bad.

-chris