llvm dev - Aug 2011 - [LLVMdev] Lying about being expanded?

Hi!

I noticed in the LegalizeDAG.cpp (SelectionDAGLegalize::LegalizeOp):

  case ISD::INIT_TRAMPOLINE:
  case ISD::FRAMEADDR:
  case ISD::RETURNADDR:
    // These operations lie about being legal: when they claim to be legal,
    // they should actually be custom-lowered.
    Action = TLI.getOperationAction(Node->getOpcode(),
Node->getValueType(0));
    if (Action == TargetLowering::Legal)
      Action = TargetLowering::Custom;
    break;

What does this mean?  Why does a target not request a node to be
custom lowered if such a thing is needed?

Also, I grepped for 'setOperationAction(ISD::TRAMPOLINE' and the
operation is 'Custom' in every instance.  Should ISD::TRAMPOLINE be
removed from this case?

Thanks!

-- 
Sanjoy Das
http://playingwithpointers.com

Hi Sanjoy,
> I noticed in the LegalizeDAG.cpp (SelectionDAGLegalize::LegalizeOp):
>
>    case ISD::INIT_TRAMPOLINE:
>    case ISD::FRAMEADDR:
>    case ISD::RETURNADDR:
>      // These operations lie about being legal: when they claim to be
legal,
>      // they should actually be custom-lowered.
>      Action = TLI.getOperationAction(Node->getOpcode(),
> Node->getValueType(0));
>      if (Action == TargetLowering::Legal)
>        Action = TargetLowering::Custom;
>      break;
>
> What does this mean?  Why does a target not request a node to be
> custom lowered if such a thing is needed?
as far as I know all nodes are considered to be legal by default.  Thus I
guess the comment is confused: most likely some target forgot to declare
them as custom, and someone hacked this in rather than fixing the target.
> Also, I grepped for 'setOperationAction(ISD::TRAMPOLINE' and the
> operation is 'Custom' in every instance.  Should ISD::TRAMPOLINE be
> removed from this case?
Probably they should all be removed, and possibly some targets fixed to
declare them as Custom.

Ciao, Duncan.