[llvm-commits] metadata.h/cpp review stuff

[Chris Lattner]

On Oct 20, 2009, at 3:10 PM, Devang Patel wrote:

>>>
>>> Metadata used by another metadata is counted as regular uses.  
>>> Metadata
>>> used by non-metadata values is not a normal use (it is invisible to
>>> the non-metadata value). This is why the hierarchy is based on User
>>> and operand list is only counting metadata uses.
>>
>> Ok, I see now that you're doing this.  But why? :)  What capability  
>> does this provide?  Is there another way to get it?  This  
>> capability costs a lot of complexity, memory and compile time.
>
>
> This may be useful to reduce memory pressure by allowing metadata  
> user to delete MDNode and its MDNode users. After stumbling couple  
> of times to get this, I am also wondering whether this is worth it  
> or not or is this the right approach.
>
> MDNodes are uniqued, just like Constant. However Constants become  
> zoombie if its use count is reduced to zero. This may be too  
> expensive for metadata because of possibility of high volume of  
> metadata in the IR due to various reasons.

I'm not convinced :) , what "various reasons" would cause this?   
Again, we have a lot of complexity to support a use case that isn't  
clear.

-Chris
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