On Tue, Sep 30, 2014 at 5:05 AM, Alexander Kornienko <ale...@google.com> wrote:
> > > On Tue, Sep 30, 2014 at 3:45 AM, Aaron Ballman <aa...@aaronballman.com> > wrote: > >> On Fri, Aug 22, 2014 at 12:42 PM, Chris Bieneman <be...@apple.com> wrote: >> > Starting a new thread to loop in cfe-dev and lldb-dev. For those not >> > following along there has been a thread on llvm-dev about moving the >> minimum >> > required Visual Studio version to 2013. The motivating reason is this >> will >> > allow us to take advantage of a bunch of C++11 features that are not >> > supported by MSVC 2012. According to MSDN >> > (http://msdn.microsoft.com/en-us/library/hh567368.aspx) the list is: >> > >> > * Non-static data member initializers >> > * Variadic templates >> > * Initializer lists >> > * Default template arguments for function templates >> > * Expression SFINAE >> > * Alias templates >> > * Delegating constructors >> > * Explicit conversion operators >> > * Raw string literals >> > * Defaulted and deleted functions >> > >> > From the discussion on LLVM-dev it is also believed that this may ease >> some >> > development pain as people keep occasionally breaking LLVM trunk by >> using >> > language features not available in MSVC. >> > >> > Original thread: >> > http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-August/075900.html >> > >> > Chandler’s proposal for moving forward is as follows: >> > 1) Loop in cfe-dev and lldb-dev (Done!) >> > 2) Wait until this email fully circulates in digests and LLVM Weekly so >> that >> > everyone who has an objection can voice it >> > 3) If there are no objections, Commit a change to the CMake build which >> > errors on old MSVC versions >> > 4) Revert and fix buildbots >> > 5) Repeat 3 & 4 until no issues >> > 6) Once the change is live for a week with no issues, update the >> > documentation to reflect the minimum required MSVC version as 2013 >> > >> > (http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-August/076090.html) >> > >> > Feedback is greatly appreciated. >> >> This thread has sort of stalled without a resolution. Alex, has your >> team had the opportunity to weigh in on the subject yet? >> >> We have run into a hard situation where MSVC 2012 is missing a feature >> that we are currently relying on. We made some changes to ASTMatchers >> to reduce the number of symbols generated in order to not require >> /bigobj support (see http://reviews.llvm.org/D5485). This change >> relies on function templates with default arguments, which MSVC does >> not support (it generates a C4519 error in MSVC 2012), resulting in >> red bots (http://bb.pgr.jp/builders/ninja-clang-i686-msc17-R/builds/10721 >> ). >> >> 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. >> > > We regularly stumble upon C++11 features not supported by MSVC 2012 and > have to rollback patches after some buildbot breaks. Usually, it's easy to > work around, not sure about this case. It's probably better to ask the > author of http://reviews.llvm.org/rL218616. > That CL was rolled back for 2 reasons, one of them being a missing C++11 feature from MSVC. I can easily workaround on that use case. In general, I don't mind working around the missing features. However, one works in more than one project. Each one might work with a different subset of some version of the language. Less rules to remember leads to less breakage. _Sam > > So I'm personally both hands for switching the minimal supported MSVC > version to 2013. I understand though, that by requiring MSVC 2013, instead > of missing support of some language features we could get incomplete and > buggy support. But still looks like a better alternative to me. > > -- Alex > > >> Thanks! >> >> ~Aaron >> >> >
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