[LLVMdev] Re: gcc like attributes and annotations

[Chris Lattner]

On Fri, 24 Feb 2006, Reid Spencer wrote:
> In thinking about the "right" way to do this, I came up with the idea of
> a single "blob" of data that could be appended to a Module. This single
> "annotation" would always be ignored by LLVM, would not require
> significant additional space to construct,

If you're talking about a blob of binary data, which does not have 
"pointers" into the LLVM code, this is fine.  However, there is no reason 
it needs to be stored "in" the BC format.  It can live "next" to it in the 
same file without impacting the bc format.

> and there is already a
> mechanism for constructing the information via the bytecode reader's
> handler interface (might need some extension).

Not clear.  If you're having "pointers" from the blob into the LLVM code 
(which I believe you would need for it to be useful), then the compiler 
code that manipulates the LLVM IR has to be aware of these pointers, must 
be able to update them when it makes changes, etc. This is extremely 
nontrivial: exactly the same problem as full fledged annotations.

Additionally, the LLVM linker would have to know how to merge these blobs 
of data (simple concatenation would be fine, more complex things probably 
not).

> (JIT/storage/etc).  The only question is: how do multiple tools avoid
> collision in this approach. Some kind of registry or partitioning of the
> data could likely solve that.

Also an issue.

-Chris

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