Add -fauto-profile option to Clang driver

[Diego Novillo]

On Tue, Oct 22, 2013 at 6:25 PM, Chandler Carruth <chandlerc at google.com> wrote:

> - I would personally prefer the intent to be explicit. The more I think
> about it the less I like one flag activating N different kinds of PGO based
> on the file type. It makes it too easy to typo a filename and get different
> (unexpected) behavior.

OK, so you'd prefer a family of flags then?  -fprofile-<kind>-use=...

This would imply a slight asymmetry in flag names with the
instrumentation based profiles, unless we renamed -fprofile-generate
to something like -fprofile-instr-generate. But I don't think we need
to be that fussy.

> - I dislike having flag A which changes flag B's behavior where possible to
> avoid. It makes it much harder to manipulate things through append-based
> build systems' flag management.

My inclination was to simply use -fprofile-generate and -fprofile-use.
The -fprofile-use flag would have file type auto-detection. I agree
that we could have scenarios where -fprofile-use surprises with
unexpected behaviour. In which case, -fprofile-<kind>-use or
-fprofile-use=:kind:filename (or some other variant) could be used.


Diego.