llvm dev - Mar 2012 - [LLVMdev] llvm::Type as llvm::Value in metadata

Hi all,

I've a question about something that's bothering me for quite some time
now: why is a llvm::Function seen as a llvm::Value (in a sense that
llvm::Function is a subclass of llvm::Value), but llvm::Type is not? Should they
not - technically seen - be equal?

And to ask a concrete question: is there any way to store a reference to a
llvm::Type within the LLVM metadata? As far as I know, the MD nodes take only
llvm::Values, so I see no way of storing a reference to a type; it would be a
nice thing to be able to store such informations, e.g. when using the metadata
to store some more user-specific informations about the module.

Hope someone has a nice idea about this!


Greetings

Marcus

On Mon, Mar 26, 2012 at 3:08 PM, Marcus Frenkel
<marcus.frenkel at fernuni-hagen.de> wrote:
> Hi all,
>
> I've a question about something that's bothering me for quite some
time now: why is a llvm::Function seen as a llvm::Value (in a sense that
llvm::Function is a subclass of llvm::Value), but llvm::Type is not? Should they
not - technically seen - be equal?
llvm::Function is a subclass of llvm::Value because you can use a
llvm::Function as a value (of type pointer-to-function).  The same is
not true for llvm::Type.

-Eli

On Tue, Mar 27, 2012 at 01:55 AM, Eli Friedman <eli.friedman at gmail.com>
wrote:
> On Mon, Mar 26, 2012 at 3:08 PM, Marcus Frenkel
> <marcus.frenkel at fernuni-hagen.de> wrote:
>> Hi all,
>>
>> I've a question about something that's bothering me for quite
some time now: why is a llvm::Function seen as a llvm::Value (in a sense that
llvm::Function is a subclass of llvm::Value), but llvm::Type is not? Should they
not - technically seen - be equal?
>
> llvm::Function is a subclass of llvm::Value because you can use a
> llvm::Function as a value (of type pointer-to-function).  The same is
> not true for llvm::Type.
Yeah, I know that (in fact, I hoped to express exactly that ;) ). The question
is, why is that so? And how can you store references to llvm::Types in the
metadata section of a module?


Greetings,

Marcus

Hi Marcus,
> And to ask a concrete question: is there any way to store a reference to a
llvm::Type within the LLVM metadata?
Not directly, but you can store a null value (Constant::getNullValue()) 
of the respective type.

Cheers,
Clemens

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>> And to ask a concrete question: is there any way to store a reference
to a llvm::Type within the LLVM metadata?
>
> Not directly, but you can store a null value (Constant::getNullValue())
> of the respective type.
>
> Cheers,
> Clemens
Hi Clemens,

I thought about this already, yes. It would still require me to know that a
specific information in the metadata refers to a type (which originally I wanted
to avoid), but I guess it can't be helped and I have to implement it that
way.


So long,

Marcus