[llvm-dev] VModuleKey K not valid here

[Dibyendu Majumdar via llvm-dev]

Hi Lang,

On Tue, 13 Aug 2019 at 23:04, Lang Hames <lhames at gmail.com> wrote:
>
>> Yes indeed that is what happened. So to prevent that I need to check
>> if VModuleKey was ever initialized ... how do I do that? I would have
>> to have to add another flag to track the initialized state.
>> The reason for it not being initialized is that sometimes I cannot
>> generate JIT code because some bytecode is not yet supported.
>
>
> I'm not sure I follow. In ORCv1 VModuleKeys are just integers: initialization is up to you, and the standard way to get a unique key is to always initialize keys by calling ExecutionSession::allocateVModuleKey(). The intent is that you should use a unique key for each module that you add, and keep a copy of the key if it is associated with a module if you want to be able to remove that module later. E.g.
>
> // Module that I will never want to remove:
> CODLayer.addModule(ES.createVModuleKey(), std::move(M)); // unique throwaway key.
>
> // Module that I want to be able to remove later:
> auto TemporaryModuleKey = ES.createVModuleKey();
> CODLayer.addModule(TemporaryModuleKey, std::move(M));
> // Do stuff.
> CODLayer.removeModule(TemporaryModuleKey);
>
> The main use cases of removable modules that I'm aware of are: (1) temporary expressions in REPLs, and (2) lower-optimized modules in re-optimizing JITs. In the former case you can usually name the key individually (as above). In the latter case you usually want to stash it in a map or context object somewhere and remove it after you've replaced the low-optimization-level code with a higher optimization level.
>

Okay maybe I am doing something wrong. I am using:

llvm::orc::VModuleKey K = ES->allocateVModule();

My point was that suppose whether I added the module or not in the way
you suggest, I still need to know which value of they VModuleKey is
'invalid'. In the example assume that CODLayer.addModule() is never
called sometimes. So how do you know whether to call removeModule()?


Regards
Dibyendu