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

[Eric Fiselier]

I added support for "LLVM_USE_SANITIZER" when building and testing last
week.

I've also noticed that when I use cmake to build libc++ in tree there are
already some existing messages about
building different instrumented libc++ versions. I'm not quite sure what
those are about though. They are not coming from libc++.

/Eric


On Tue, Aug 26, 2014 at 10:44 AM, Kostya Serebryany <kcc at google.com> wrote:

>
>
>
> On Tue, Aug 26, 2014 at 2:31 AM, Evgeniy Stepanov <
> eugeni.stepanov at gmail.com> wrote:
>
>> As Chandler said, disabling extern templates may help with some simple
>> tests, but the only reliable way to get rid of MSan false positives is
>> linking with instrumented libc++.
>>
>> We should concentrate on making is easier to build and use
>> instrumented libc++ instead.
>>
> Yes, please!
>
>>
>> On Mon, Aug 18, 2014 at 6:30 AM, Eric Fiselier <eric at efcs.ca> wrote:
>> >> 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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>> > cfe-commits at cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>> >
>>
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