[cfe-dev] Warnings on Opt passes

[Renato Golin]

Hi all,

I was discussing this with a few folks at the dev meeting and it would be
interesting for some passes to print some warnings on a later stage than
the front-end, in special cases, especially if line information is kept and
available at that stage. Is this possible today?

My main concern is not correctness, that should have been taken care by the
front-end and the sanitizers, but things like we already do with the debug
messages, only less verbose, and possibly formatted in a special way, so
that other front-end tools can read and propose changes to the code.

I don't have a clear picture of it yet in my mind, but I was thinking of
hints like "this loop could be vectorized if you added a restrict keyword
to your pointers".

The vectorizer doesn't know if they alias, so it prints the warning. Then
another front-end tool could read this and do some code analysis and tell
the user if there is at least a few cases in the call graph in which they
can't alias, and propose some code changes.

This can also be used to raise bugs. Even though the debug info is already
good enough for it, a flag in Clang to enable these non-verbose warnings
would be more effective than a list of debug messages, and maybe the user
could even figure it out by him/herself before sending the email.

So instead of an email like "why doesn't my loop vectorize?", we get a bug
report "implement THIS and THAT in the vectorizer", with an example of the
loop.

Does that make sense? This could be a nice GSOC project...

cheers,
--renato
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