[llvm-dev] returning from LowerOperation()

[Jonas Paulsson via llvm-dev]

Hi Eli,

I would like to clarify generally what the difference is between 
returning SDValue() and Op (input argument unchanged) from LowerOperation()?

My understanding is that returning SDValue() means that Target gives up, 
and the common code is supposed to handle it. Returning Op, the 
unchanged argument, means that the Target is happy with the node as it 
is, and the common code can move on to something else.

Are there any exceptions to this? Is this commented on anywhere? Are 
there cases where the target should not return SDValue()?

Thanks,

Jonas