[llvm-dev] Upgrading to MSVC 2015

Sat Jul 30 17:53:47 PDT 2016

> -----Original Message-----
> From: aaron.ballman at gmail.com [mailto:aaron.ballman at gmail.com] On Behalf
> Of Aaron Ballman
> Sent: Saturday, July 30, 2016 12:41 PM
> To: Robinson, Paul
> Cc: Zachary Turner; Sean Silva; Piotr Padlewski; llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] Upgrading to MSVC 2015
> 
> On Sat, Jul 30, 2016 at 1:58 PM, Robinson, Paul <paul.robinson at sony.com>
> wrote:
> >
> >
> >> -----Original Message-----
> >> From: aaron.ballman at gmail.com [mailto:aaron.ballman at gmail.com] On
> Behalf
> >> Of Aaron Ballman
> >> Sent: Friday, July 29, 2016 2:19 PM
> >> To: Zachary Turner
> >> Cc: Sean Silva; Robinson, Paul; Piotr Padlewski; llvm-
> dev at lists.llvm.org
> >> Subject: Re: [llvm-dev] Upgrading to MSVC 2015
> >>
> >> There are not that many people making commits to working around MSVC
> >> 2013 as I think are claimed
> >
> > CGOpenMPRuntime.cpp had 4 patches this week trying to make VS2013 happy.
> > I can tell they were because of VS2013 because the public PS4 bot has
> > VS2015 and it didn't seem to have the same problems.
> 
> Hmmm, I don't see any mention in the code itself about changes to
> appease MSVC 2013, so that's why it didn't come up in my searches. We
> usually ask people working around buggy compilers to leave a FIXME in
> there so we can remove compiler hacks (but obviously, we don't manage
> to catch all of them), so if you run into anything like this again,
> please try to put in a FIXME if it's appropriate.

Ah, okay, was not aware of that policy.  I'll try to keep that in mind
if it comes up again.  It looks like other people with a more vested
interest in that module have also been working on it, so I'm not sure
exactly what its current state is; if my hacks are still there Monday
then I'll look at adding FIXME comments.
Thanks,
--paulr

> 
> > Maybe it was just bad luck that we put up an internal VS2013 bot when it
> > happened, but it has been an incredible time-sink for me this week.
> 
> I'm sorry it's been a time sink for you!
> 
> > Note I do not want to advance the timetable, I just want to make sure
> > that the actual problems aren't dismissed too readily.
> 
> Agreed -- if we have compiler problems that are causing a lot of pain,
> I think it's a good idea to discuss bumping the time table. However,
> we have problems with *every* compiler from time to time. For
> comparison, when we dropped MSVC 2012 early we had frequent
> (weekly-ish?) issues that we would run up against that 2013 had
> already fixed, the workarounds were cumbersome, and 2013 had a looming
> release date. We do run into issues with 2013 (I helped someone work
> around one yesterday, in fact), so it's good for us to keep track of
> those situations to help make informed decisions, but whether we're at
> the point of deviating from our compiler support policy or not is less
> clear to me.
> 
> ~Aaron
> 
> > --paulr
> >
> >> (there are certainly a lot of commits for
> >> working around MSVC in general, however). A quick search through the
> >> code base shows there are 8 instances where we've worked around MSVC
> >> 2013 issues (there may be more that someone worked around in an ad hoc
> >> manner and did not mark). We definitely had *a lot* more when we
> >> dropped MSVC 2012 early. The primary issues people are working around
> >> are constexpr support, which is important but certainly not critical,
> >> and still some occasional issues with move constructors not being
> >> synthesized as expected, which is also pretty simple to work around
> >> (and is usually an optimization loss more than a functionality loss).
> >>
> >> As MSVC 15 starts getting closer to the RTM stages, I think we should
> >> definitely consider the switch more strongly, but with it still in
> >> Preview mode, I think it's premature to drop support for MSVC 2013 at
> >> this time.
> >>
> >> ~Aaron
> >>
> >> On Fri, Jul 29, 2016 at 5:02 PM, Zachary Turner <zturner at google.com>
> >> wrote:
> >> > FWIW, no objections from me, after all I proposed this 3 months ago
> :)
> >> >
> >> > Probably Aaron Ballman should comment though since the primary
> objection
> >> > last time was his.
> >> >
> >> > On Fri, Jul 29, 2016 at 2:00 PM Sean Silva <chisophugis at gmail.com>
> >> wrote:
> >> >>
> >> >> On Fri, Jul 29, 2016 at 1:23 PM, Robinson, Paul via llvm-dev
> >> >> <llvm-dev at lists.llvm.org> wrote:
> >> >>>
> >> >>> There are certainly enough people making commits that work with
> VS2015
> >> >>> but not VS2013 that the "would it be useful" question is pretty
> well
> >> >>> answered.  I've already brought up the idea on my team, as it's
> >> obviously
> >> >>> coming and we need time to coordinate with internal consumers of
> the
> >> >>> toolchain.
> >> >>
> >> >>
> >> >> Also, we have an increasing number of parts of the codebase that are
> >> >> working around VS2013's inability to generate move constructors.
> >> >> This is all over the new PM code and the passes ported to the new
> PM.
> >> >> It has caused me personally hours of lost time and generally
> penalizes
> >> >> good coding practices (exporting lifetime management to RAII is only
> so
> >> >> convenient if you can't have a move-only type like a unique_ptr
> without
> >> >> manually writing out move constructor/assign; and the diagnostics
> when
> >> this
> >> >> VS2013 deficiency raises its head are.... confusing).
> >> >>
> >> >> -- Sean Silva
> >> >>
> >> >>
> >> >>>
> >> >>> --paulr
> >> >>>
> >> >>>
> >> >>>
> >> >>> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf
> Of
> >> >>> Zachary Turner via llvm-dev
> >> >>> Sent: Friday, July 29, 2016 11:35 AM
> >> >>> To: Piotr Padlewski; Aaron Ballman
> >> >>> Cc: llvm-dev
> >> >>> Subject: Re: [llvm-dev] Upgrading to MSVC 2015
> >> >>>
> >> >>>
> >> >>>
> >> >>> Probably not.  It's very confusing because they are transitioning
> to a
> >> >>> new versioning scheme.  The current version if Visual Studio 2015.
> >> The next
> >> >>> version is Visual Studio 15.  The link you posted was for the RTM
> of
> >> 2015,
> >> >>> just over a year ago.  But 15 is still in Preview.  When 15 goes to
> >> RTM,
> >> >>> then we can revisit the question of making 2015 the minimum
> required
> >> >>> version.
> >> >>>
> >> >>>
> >> >>>
> >> >>> On Fri, Jul 29, 2016 at 11:29 AM Piotr Padlewski
> >> >>> <piotr.padlewski at gmail.com> wrote:
> >> >>>
> >> >>> https://www.visualstudio.com/en-us/news/vs2015-vs.aspx
> >> >>>
> >> >>>
> >> >>>
> >> >>> Is it time?
> >> >>>
> >> >>>
> >> >>>
> >> >>> 2016-03-31 12:03 GMT-07:00 Aaron Ballman via llvm-dev
> >> >>> <llvm-dev at lists.llvm.org>:
> >> >>>
> >> >>> On Thu, Mar 31, 2016 at 2:57 PM, Zachary Turner
> <zturner at google.com>
> >> >>> wrote:
> >> >>> >
> >> >>> >
> >> >>> > On Tue, Mar 29, 2016 at 10:42 AM Aaron Ballman
> >> <aaron at aaronballman.com>
> >> >>> > wrote:
> >> >>> >>
> >> >>> >>
> >> >>> >> Not everyone can upgrade to the latest version of the toolchain,
> >> even
> >> >>> >> if it has been released for a while. We did drop MSVC 2012
> support
> >> >>> >> early, but MSVC 2015 was in RC or RTM stages by that point, and
> we
> >> had
> >> >>> >> some pretty big incentive to upgrade early (without function
> >> templates
> >> >>> >> supporting default arguments, the AST matcher DSL made for
> really
> >> slow
> >> >>> >> compiles of Clang itself, and resulted in a larger executable
> size
> >> >>> >> among other things, IIRC).
> >> >>> >
> >> >>> >
> >> >>> > I know you mentioned that one of the reasons we upgraded to 2013
> was
> >> >>> > because
> >> >>> > 2015 was in RC or RTM.  Ironically, the day after I posted this
> MS
> >> >>> > announced
> >> >>> > Visual Studio 15 preview  (which is confusingly the version
> *after*
> >> >>> > Visual
> >> >>> > Studio 2015).
> >> >>>
> >> >>> Hah, that is confusing!
> >> >>>
> >> >>> > In any case, it's not an RC, and it's certainly not an RTM,
> >> >>> > but it is on the horizon.  So hopefully we can revisit this
> question
> >> >>> > when 15
> >> >>> > is in RC / RTM
> >> >>>
> >> >>> I think that's a great time to revisit the question (transitioning
> >> >>> sometimes takes a bit of time since we want to ask people with out
> of
> >> >>> tree needs if they're ready before dropping support for major
> >> >>> releases).
> >> >>>
> >> >>>
> >> >>> ~Aaron
> >> >>>
> >> >>>
> >> >>> _______________________________________________
> >> >>> LLVM Developers mailing list
> >> >>> llvm-dev at lists.llvm.org
> >> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >> >>>
> >> >>>
> >> >>> _______________________________________________
> >> >>> LLVM Developers mailing list
> >> >>> llvm-dev at lists.llvm.org
> >> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >> >>>
> >> >