[LLVMdev] Warnings on Opt passes

[Renato Golin]

On 9 November 2013 15:03, Henrique Santos
<henrique.nazare.santos at gmail.com>wrote:

> It seems like a difficult thing to do since we would have to keep metadata
> intact across transformations, which, AFAIK, is not done.
> mem2reg, for example, doesn't even propagate debug metadata to phi nodes,
> and I'm not really sure if it's valid to do so.
>

I understand that for most micro opts (delete, combine, coalesce, simplify,
etc), this would be pointless. But for big things, like the vectorizers, it
could be an interesting tool in addition to the sanitizers, since at that
point, we'd have a lot more information than in the front-end (vector
sizes, types, costs, etc). In those cases, I don't think we need that much
debug info.

Line information should be enough for big things, and that's reasonably
kept, even at O3. For instance, if a loop is inlined into another function,
it'll contain the original line info, which is helpful. Also, if a function
is inlined into a loop, and the SLP-vectorizer has warnings, it'll also
point to the original function. It shouldn't be hard to include the
function name in the warning (to know where it was inlined into, for
example).

I'm thinking of making the optimization passes help the front-end(s), the
same way PGO helps the optimization passes.

cheers,
--renato
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