[libcxx] r215740 - Revert "Turn off extern templates for most uses."

[Eric Fiselier]

> FWIW, I don't think that MSan was *ever* intended to not have false
positives with an uninstrumented standard library. So I really don't
understand why this is an interesting thing to dig into.

That is new information to me so I'll have to take that into consideration.
What I was trying to avoid was breaking MSAN usability for end users of
libc++.
Since its unlikely that they have a instrumented standard library it would
be nice if their system libc++ didn't always cause the first MSAN failure.

Since __attribute__((__always_inline__)) seems to cause a lot of these
failures I imagine it is possible to reduce the FP's without removing the
extern template declarations.
In that case it might still be work putting time into.

/Eric


On Sun, Aug 17, 2014 at 8:24 PM, Howard Hinnant <howard.hinnant at gmail.com>
wrote:

> On Aug 17, 2014, at 9:26 PM, Justin Bogner <mail at justinbogner.com> wrote:
>
> > Howard Hinnant <howard.hinnant at gmail.com> writes:
> >> On Aug 17, 2014, at 9:06 PM, Justin Bogner <mail at justinbogner.com>
> wrote:
> >>
> >>> I really don't think it's worth the cost of insantiating these very
> >>> fundamental templates in *every single user* to work around a
> limitation
> >>> in the memory sanitizer. This is an unreasonable amount of overhead for
> >>> standard library types.
> >>
> >> Always measure.  I’m not saying you’re wrong.  I’m saying you’re
> >> stating a performance conclusion without measurements (which should
> >> never be acceptable).
> >
> > I did measure :) Though, I sent it to llvm-dev and it probably should've
> > been cfe-dev. Sorry about that.
> >
> > http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-August/075793.html
>
> Ah, I have not been monitoring llvm-dev.  Thank you for the link.
>
> Howard
>
>
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