[llvm-commits] patch: use CallbackVH for metadata

[Nick Lewycky]

Chris Lattner wrote:
> On May 5, 2009, at 11:15 PM, Nick Lewycky wrote:
> 
>> This patch switches MDNode to using CallbackVH and adds a special  
>> typeless "null" keyword that means "(Value*)0" within a metadata  
>> node. Also change MDNode construction to accept Value* even though  
>> we don't really permit non-Constant values yet.
> 
> Looks nice.  Please split MDNode (and the VH.h #include) out to a new  
> MDNode.h file.

Done. I've attached the updated patch. Okay to commit?

> In ElementVH, what is the right behavior when RAUW and delete are  
> called?  Shouldn't these go back through to be recursively uniqued,  
> like what happens for Constants?

The comment block on MDNode says so. ElementVH's delete and RAUW 
implementations call MDNode::replaceElement which uses MDNode::get to 
find the replacement and uncheckedReplaceAllUsesWith to affect it. You 
can see that it works from the last two tests in MetadataTest.

Nick
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