[LLVMdev] Metadata

[Chris Lattner]

On Feb 10, 2010, at 10:20 AM, David Greene wrote:

> On Wednesday 10 February 2010 11:46:25 Chris Lattner wrote:
> 
>>> There is not any mechanism to attach metadata with SDNode or
>>> MachineInstrs today.
>> 
>> For nontemporal stores, you wouldn't want to do this anyway.  In
>> selectiondag builder, you'd want to check the store instruction to see if
>> it has the metadata on it, and if so make a different ISD opcode or
>> something.
> 
> Ah, ok, I could do that.  The way we did this here was to add some information
> into the SDNode and then write a TableGen predicate to check it, generating
> a different kind of store instruction.  This avoided the need for a new target 
> ISD opcode.
> 
> In general, is one method preferred over the other?  That is, if target-
> specific ISD opcodes can be avoided, should we avoid them?
> 
> Is there any reason we would not want to support metadata on SDNodes,
> other than the cost of implementing it?  We don't necessarily need to do that 
> now.  I'm just asking the question with future possibilities in mind.

I think that adding a bit to LoadSDNode and StoreSDNode would make sense.

-Chris