[LLVMdev] Metadata

David Greene dag at cray.com
Wed Feb 10 10:20:49 PST 2010

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.


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