[LLVMdev] CollectorRegistry

[Gordon Henriksen]

On 2008-07-23, at 08:58, Simon Ask Ulsnes wrote:

> I am attempting to write a garbage collector for LLVM, and the tiny  
> example in the docs at http://llvm.org/releases/2.3/docs/GarbageCollection.html 
>  gives this line:
>
>   CollectorRegistry::Add<MyCollector>
>   X("mygc", "My bespoke garbage collector.");
>
> My question is now: Am I supposed to instantiate my collector  
> manually, and tell LLVM about it, or can the Registry instantiate  
> it, and it that case, how to go about that? I haven't been able to  
> deduce a way to get a pointer to my collector from the doxygen docs  
> or the header files, so I hope that you can help me here. :-)


Hi Simon,

The compiler framework will instantiate and call into your Collector  
subclass automatically as required. The CollectorRegistry::Add<>  
instance advertises your class to the framework so it can do this.  
Your Collector class needs to have a default constructor in order to  
insantiate the Add<> template.

The framework decides which Collector to use based upon the 'gc'  
attribute of a function:

define void @f() gc "mygc" {
   ...
}

This string must correspond to the first argument to the  
CollectorRegistry::Add<> constructor.

The second argument to the constructor is, I think, "purely  
informational" for collectors. For the related TargetMachineRegistry,  
the second argument appears in --help output.

Hope that helps,
Gordon