[LLVMdev] [cfe-dev] [RFC] Raising LLVM minimum required MSVC version to 2013 for trunk

[Aaron Ballman]

On Tue, Sep 30, 2014 at 4:57 AM, Kristof Beyls <kristof.beyls at arm.com> wrote:
>> >
>> > This is a considerably more interesting case (at least to me) than
>> > hypothetical benefits -- if we retain MSVC 2012 support, we will also
>> > require /bigobj support, have slower compile times for ASTMatcher
>> > projects, and slower benchmarks for clang-tidy. This points to
>> > concrete benefits to expediting switching away from MSVC 2012, which
>> > is why I am pinging this thread again.
>>
>> I guess I'm a little surprised that /bigobj is such a compile-time hit,
>> but haven't tried any benchmarking. Anyway, whatever works best for you.
>> --paulr
>
> I'm not 100% sure, but my understanding is that the huge number of template
> instantiations is the root cause of the compile-time hit. It's the same root
> cause that requires /bigobj to be needed, as each template instantiation
> seems to need its own section? Therefore, /bigobj in itself probably doesn't
> incur a compile-time hit, but rather the huge number of template instantiations
> produced.
> Aaron, did I understand correctly that moving to MSVC2013 would allow to
> adapt the code so that no longer a huge number of templates need to be instantiated?

That is correct -- MSVC 2013 supports the language feature needed for
that patch. That's not to say there aren't other solutions to the
problem which are portable across more compilers.

~Aaron