[LLVMdev] Clarification on the backward compatibility promises

[Sean Silva]

On Sun, Jun 22, 2014 at 2:15 AM, James Courtier-Dutton <
james.dutton at gmail.com> wrote:

> On 22 June 2014 01:18, Sean Silva <chisophugis at gmail.com> wrote:
> > Does anyone have anything else to say about .bc/.ll compatibility? It is
> > important to be clear to users about what compatibility we provide. I'd
> like
> > to get consensus about this and put it in the docs somewhere.
> >
> > -- Sean Silva
> >
>
> To make this all a bit easier, how about making clang/llvm output a
> version number at the beginning of the .ll or .bc file?
> It would then be clear which version of clang/llvm wrote the file out.
> You could then add warnings if clang/llvm thought they were
> incompatible with the older version or not.
>

I don't think that would significantly help.

For .bc, the sizes of records already implicitly hold that information in a
more fine-grained and semantic way (not tied to versions, but rather
intrinsically to the change to the IR).
For .ll, it is too easy to end up with a file that has an nonexistent or
inconsistent version number (such as a hand-written file) so we wouldn't be
able to rely on it.

Anyway, that's sort of a separate discussion. For now, I'd like to focus
strictly on deciding what guarantees we offer.

-- Sean Silva


>
> Kind Regards
>
> James
>
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