[LLVMdev] Packages

[Reid Spencer]

On Mon, 2003-11-17 at 22:44, Chris Lattner wrote:

> We already have never, ever, delete this flags.  "weak" and external
> linkage both guarantee that.  If there can be an external caller of some
> function, for example, the optimizer CANNOT delete it, nor can it change
> it's interface.

Interesting, I wouldn't have assumed that given LLVM's support for IPO.
If you find that a function is never used when doing final linking of a
program, why not delete it?  Just curious .. and off topic ..

> 
> > If that was the case, I could use the full expression of LLVM assembly
> > language to describe my source level information.  No?
> 
> I'm not sure exactly what you mean here, but yes, in principle, you should
> be able to do exactly that.  You are limited to the LLVM type system and
> such, but if that is sufficient, yes.

I just mean that I could define LLVM types to define the structure of my
source level information. There actually isn't much that's needed. Some
tables, a few bit masks, a couple structures to group things together.
So, LLVM types are fine.
> 
> > This being the case, I could emit a function in each module that returns
> > the source level information. To look at it, I just JIT load the module
> > and call the function.  Any barriers to doing this?
> 
> None at all!

Not so fast! I have a couple issues I need your clarification on:

      * The source level information could reference a function (in
        fact, it would reference all of them!). Could this reference to
        the function thwart optimization? Same for global variables,
        types, etc.
      * If I wanted to create a function named "GetModuleInfo" in every
        module, wouldn't that cause link time symbol redefinition and
        the resulting errors if it was "externally visible" linkage? If
        I use weak linkage I avoid that problem, but then can I call the
        function directly after JIT loading? Isn't it "internal" to the
        module?

(P.S. I read the entire discussion on "GCC tree linkage types" on the
GCC list and got myself totally confused about what is and isn't
"linkonce", etc.  Had to go back to the LLVM Language Reference to
straighten myself out again :)
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