llvm dev - Nov 2013 - [LLVMdev] [cfe-dev] RFC: A proposal to move toward using C++11 features in LLVM & Clang / bounding support for old host compilers

(re-sending to the actual mailing lists... go go gadget typos!)


On Sun, Oct 27, 2013 at 2:23 AM, Chandler Carruth <chandlerc at
google.com>wrote:
> Greetings,
>
> This has been discussed many times, and there are a lot of pro's and
con's
> on each side, but increasingly I think the project needs to draw a line in
> the sand and put in place long-term policies around support for building
> LLVM & Clang with older C++ toolchains. It also would have the benefit
of
> removing divergence between LLVM sub-projects already using C++11 features.
> As they have grown in popularity and as code moves back and forth across
> project boundaries, I think this is a growing strain.
>
> I am seriously concerned that if we don't do this now, we will miss out
on
> the accelerating trend of C++ as a language.
>
> Concrete long term proposal:
>
> We support building with C++ toolchains which were released and widely
> available on their respective target platforms at least 2 years prior to
> the next 6-month-cycle release. Immediately after each branch of a release,
> mainline can move the bar forward by 6 months. Thus, each release should
> build with the four previous releases.
>
> Some observations:
> - I specifically am wording this to enable the mainline to use features
> sooner. People who are unable to use an *even more* modern toolchain will
> necessarily stay with each release.
> - This is an aggressive timeline. That is intentional. There is increasing
> pressure for LLVM to make use of new C++ language and library features.
> - There is always the option of checking out an old release, building it,
> and then using that compiler to build the latest release or to build the
> mainline compiler.
> - The goal is to only change the supported toolchain set and thus C++
> dialect after a release branches to avoid confusion, churn, and impeding QA
> on a release. People can check out trunk and get an idea of whether they
> will have problems with the next release.
> - I have historically been more conservative on this topic, but listening
> to many people and looking at some of the C++ features we are missing, I
> think the right strategy for the project is a more aggressive one.
>
>
> One short term caveat: Windows is special.
>
> I don't think we should follow the 2-year rule for Windows. It really
is
> special for at least three reasons:
> 1) We can't bootstrap on Windows. While there is tons of exciting work
> going on here to change that, even then the quality of Windows support is
> likely to change very rapidly.
> 2) Visual Studio's C++ support moved very slowly for a long time, and
is
> now improving at an amazing rate. We shouldn't be hampered by past
problems
> and should take advantage of this recent progress.
> 3) We have less insight into when new versions of the MSVC++ toolchain
> will arrive.
>
> So my suggestion is that, at least during the rapid evolution of VS's
> C++11 support and Clang's Windows support, we support building with the
> most recent 2 versions of VS available at the *prior* release. For example
> when we branch for 3.4, the two versions will be 2012 and 2013. Those two
> would be supported on mainline from then through 3.5, and when we branch
> for 3.5 we would re-evaluate.
>
> NOTE: This would drop support for VS 2010!!! That is a huge change, hence
> my suggesting it only *after* we branch for 3.4. It gives us an entire
> release cycle of notice for people relying on it.
>
>
> Now for the carrot: if we go with this plan, then immediately after
> branching for 3.4,  we would be able to use the vast majority of C++11
> features, targeting the following as the oldest toolchains supported
> through the 3.5 release timeframe:
>
> GCC 4.7
> Clang 3.1
> VS 2012
>
> Some notable features we would get to use:
>
> - r-value references, move semantics, etc
> - auto
> - range for loops
> - lambdas
> - static_assert
> - nullptr
> - std::unique_ptr, std::tuple, some other nice library stuff
>
>
> These days, this list seems increasingly worth the cost of forcing users
> to get a modern toolchain onto their systems.
>
> -Chandler
>
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>> GCC 4.7
>> Clang 3.1
>> VS 2012
Xcode 4.2's clang?

Do we already have bots with all these versions?

Cheers,
Rafael

On Sun, Oct 27, 2013 at 2:23 AM, Chandler Carruth <chandlerc at
google.com> wrote:
> Greetings,
> 
> This has been discussed many times, and there are a lot of pro's and
con's on each side, but increasingly I think the project needs to draw a
line in the sand and put in place long-term policies around support for building
LLVM & Clang with older C++ toolchains. It also would have the benefit of
removing divergence between LLVM sub-projects already using C++11 features. As
they have grown in popularity and as code moves back and forth across project
boundaries, I think this is a growing strain.
Awesome, thank you for spearheading this discussion.  We really need to move to
some C++'11 support, it is just a question of how and when.  We also had a
discussion from a few months ago about this, can you summarize where we left
off?  I thought there was a tentative plan for LLVM 3.4 (or maybe it was after
3.4 branched).

> I am seriously concerned that if we don't do this now, we will miss out
on the accelerating trend of C++ as a language.
I'm not worried about the "accelerating trend", I just think
we'll all be more productive.
> Concrete long term proposal:
> 
> We support building with C++ toolchains which were released and widely
available on their respective target platforms at least 2 years prior to the
next 6-month-cycle release. Immediately after each branch of a release, mainline
can move the bar forward by 6 months. Thus, each release should build with the
four previous releases.
I don't think it makes sense to have a hard policy like this.  It is fine to
have a goal that allows us to continue picking up new features over time, but I
think each such change will have to be discussed (at length) with the specifics
of which interesting host configurations we would be dropping.
> Some observations:
> - I specifically am wording this to enable the mainline to use features
sooner. People who are unable to use an *even more* modern toolchain will
necessarily stay with each release.
> - This is an aggressive timeline. That is intentional. There is increasing
pressure for LLVM to make use of new C++ language and library features.
> - There is always the option of checking out an old release, building it,
and then using that compiler to build the latest release or to build the
mainline compiler.
> - The goal is to only change the supported toolchain set and thus C++
dialect after a release branches to avoid confusion, churn, and impeding QA on a
release. People can check out trunk and get an idea of whether they will have
problems with the next release.
> - I have historically been more conservative on this topic, but listening
to many people and looking at some of the C++ features we are missing, I think
the right strategy for the project is a more aggressive one.
I really want this to happen, but it needs to be done in the right way,
balancing the cost to the community to obsolete old configurations.  As such, I
agree with everything except your last point here :-)
> One short term caveat: Windows is special.
I don't see how it is special.  We should just look at all of the compilers
we need to support, and factor that set in.  We should continue to increment the
baseline compilers over time, but a global "two year old compilers
only" policy doesn't make sense to me.  I also think that windows will
be the lowest bar anyway.
> Now for the carrot: if we go with this plan, then immediately after
branching for 3.4,  we would be able to use the vast majority of C++11 features,
targeting the following as the oldest toolchains supported through the 3.5
release timeframe:
> 
> GCC 4.7
> Clang 3.1
> VS 2012
This seems overly aggressive to me.  Why not start by baselining at VC++ 2010,
and bump up everything else to match?  That would give us some basic C++'11
features for 3.4, then we could bump it up to VS 2012 in 3.5 if that goes well.

-Chris
> 
> Some notable features we would get to use:
> 
> - r-value references, move semantics, etc
> - auto
> - range for loops
> - lambdas
> - static_assert
> - nullptr
> - std::unique_ptr, std::tuple, some other nice library stuff
> 
> 
> These days, this list seems increasingly worth the cost of forcing users to
get a modern toolchain onto their systems.

On Sun, Oct 27, 2013 at 02:24:58AM -0700, Chandler Carruth
wrote:
> > Now for the carrot: if we go with this plan, then immediately after
> > branching for 3.4,  we would be able to use the vast majority of C++11
> > features, targeting the following as the oldest toolchains supported
> > through the 3.5 release timeframe:
> >
> > GCC 4.7
> > Clang 3.1
> > VS 2012
> >
> > Some notable features we would get to use:
> >
> > - r-value references, move semantics, etc
> > - auto
> > - range for loops
> > - lambdas
> > - static_assert
> > - nullptr
> > - std::unique_ptr, std::tuple, some other nice library stuff
It would be nice to keep the list to things that don't require too much
support from the STL implementation. Locale support and std::thread in
the various forms are a real show stopper for bootstrapping otherwise.

Joerg

On Oct 27, 2013, at 11:18 AM, Chris Lattner <clattner at apple.com> wrote:
> On Sun, Oct 27, 2013 at 2:23 AM, Chandler Carruth <chandlerc at
google.com> wrote:
>> Greetings,
>> 
>> This has been discussed many times, and there are a lot of pro's
and con's on each side, but increasingly I think the project needs to draw a
line in the sand and put in place long-term policies around support for building
LLVM & Clang with older C++ toolchains. It also would have the benefit of
removing divergence between LLVM sub-projects already using C++11 features. As
they have grown in popularity and as code moves back and forth across project
boundaries, I think this is a growing strain.
> 
> Awesome, thank you for spearheading this discussion.  We really need to
move to some C++'11 support, it is just a question of how and when.  We also
had a discussion from a few months ago about this, can you summarize where we
left off?  I thought there was a tentative plan for LLVM 3.4 (or maybe it was
after 3.4 branched).
I have a quick question on this. Apology if this has already been answered in
the past. Am I correct in assuming this also force changes to other projects
which link in LLVM?

Evan
> 
> 
>> I am seriously concerned that if we don't do this now, we will miss
out on the accelerating trend of C++ as a language.
> 
> I'm not worried about the "accelerating trend", I just think
we'll all be more productive.
> 
>> Concrete long term proposal:
>> 
>> We support building with C++ toolchains which were released and widely
available on their respective target platforms at least 2 years prior to the
next 6-month-cycle release. Immediately after each branch of a release, mainline
can move the bar forward by 6 months. Thus, each release should build with the
four previous releases.
> 
> I don't think it makes sense to have a hard policy like this.  It is
fine to have a goal that allows us to continue picking up new features over
time, but I think each such change will have to be discussed (at length) with
the specifics of which interesting host configurations we would be dropping.
> 
>> Some observations:
>> - I specifically am wording this to enable the mainline to use features
sooner. People who are unable to use an *even more* modern toolchain will
necessarily stay with each release.
>> - This is an aggressive timeline. That is intentional. There is
increasing pressure for LLVM to make use of new C++ language and library
features.
>> - There is always the option of checking out an old release, building
it, and then using that compiler to build the latest release or to build the
mainline compiler.
>> - The goal is to only change the supported toolchain set and thus C++
dialect after a release branches to avoid confusion, churn, and impeding QA on a
release. People can check out trunk and get an idea of whether they will have
problems with the next release.
>> - I have historically been more conservative on this topic, but
listening to many people and looking at some of the C++ features we are missing,
I think the right strategy for the project is a more aggressive one.
> 
> I really want this to happen, but it needs to be done in the right way,
balancing the cost to the community to obsolete old configurations.  As such, I
agree with everything except your last point here :-)
> 
>> One short term caveat: Windows is special.
> 
> I don't see how it is special.  We should just look at all of the
compilers we need to support, and factor that set in.  We should continue to
increment the baseline compilers over time, but a global "two year old
compilers only" policy doesn't make sense to me.  I also think that
windows will be the lowest bar anyway.
> 
>> Now for the carrot: if we go with this plan, then immediately after
branching for 3.4,  we would be able to use the vast majority of C++11 features,
targeting the following as the oldest toolchains supported through the 3.5
release timeframe:
>> 
>> GCC 4.7
>> Clang 3.1
>> VS 2012
> 
> This seems overly aggressive to me.  Why not start by baselining at VC++
2010, and bump up everything else to match?  That would give us some basic
C++'11 features for 3.4, then we could bump it up to VS 2012 in 3.5 if that
goes well.
> 
> -Chris
> 
>> 
>> Some notable features we would get to use:
>> 
>> - r-value references, move semantics, etc
>> - auto
>> - range for loops
>> - lambdas
>> - static_assert
>> - nullptr
>> - std::unique_ptr, std::tuple, some other nice library stuff
>> 
>> 
>> These days, this list seems increasingly worth the cost of forcing
users to get a modern toolchain onto their systems.
> 
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Oct 27, 2013, at 12:07 PM, Óscar Fuentes <ofv at wanadoo.es>
wrote:
> Chris Lattner <clattner at apple.com> writes:
> 
>>> One short term caveat: Windows is special.
> 
> s/Windows/Visual Studio.
> 
> MinGW has the latest and greatest gcc.
> 
>> I don't see how it is special.
> 
> It is special, sadly, and I'm not talking about C++11 support only, but
> about the policies MS follows which too often makes very inconvenient
> (or even impossible) to upgrade to newer VS versions. The latest example
> that comes to mind was the release of VS2012: they removed Windows XP
> support, as if upgrading the OS is a non-issue if you ask for it to your
> users on a polite tone. An uproar followed and they backpedaled on a
> service pack some months later, but that not always happens.
I'm sorry, let me clarify.  I'm saying that MSVC shouldn't be
special from an LLVM policy perspective.  We shouldn't have a general rule
with an exception for MSVC: we should have a general rule that includes MSVC
user's requirements as well.

This is why I don't like a general rule of "anything older than 2 years
isn't supported".
>>> Now for the carrot: if we go with this plan, then immediately after
>>> branching for 3.4, we would be able to use the vast majority of
>>> C++11 features, targeting the following as the oldest toolchains
>>> supported through the 3.5 release timeframe:
>>> 
>>> GCC 4.7
>>> Clang 3.1
>>> VS 2012
>> 
>> This seems overly aggressive to me. Why not start by baselining at
>> VC++ 2010, and bump up everything else to match?
> 
> IIRC the only significant difference among VS 2012 and VS 2010 is range
> for loops.
Which is really sad, given how nice they are, but I think it would be huge
progress to move LLVM 3.4 to require the VS 2010 feature set (and the
corresponding GCC/clang/etc versions).  We can move up to VS 2012 as a second
step and second discussion.

-Chris

On Sun, Oct 27, 2013 at 5:09 PM, Chris Lattner <clattner at apple.com>
wrote:
> On Oct 27, 2013, at 12:07 PM, Óscar Fuentes <ofv at wanadoo.es>
wrote:
>> Chris Lattner <clattner at apple.com> writes:
>>
>>>> One short term caveat: Windows is special.
>>
>> s/Windows/Visual Studio.
>>
>> MinGW has the latest and greatest gcc.
>>
>>> I don't see how it is special.
>>
>> It is special, sadly, and I'm not talking about C++11 support only,
but
>> about the policies MS follows which too often makes very inconvenient
>> (or even impossible) to upgrade to newer VS versions. The latest
example
>> that comes to mind was the release of VS2012: they removed Windows XP
>> support, as if upgrading the OS is a non-issue if you ask for it to
your
>> users on a polite tone. An uproar followed and they backpedaled on a
>> service pack some months later, but that not always happens.
>
> I'm sorry, let me clarify.  I'm saying that MSVC shouldn't be
special from an LLVM policy perspective.  We shouldn't have a general rule
with an exception for MSVC: we should have a general rule that includes MSVC
user's requirements as well.
>
> This is why I don't like a general rule of "anything older than 2
years isn't supported".
>
>>>> Now for the carrot: if we go with this plan, then immediately
after
>>>> branching for 3.4, we would be able to use the vast majority of
>>>> C++11 features, targeting the following as the oldest
toolchains
>>>> supported through the 3.5 release timeframe:
>>>>
>>>> GCC 4.7
>>>> Clang 3.1
>>>> VS 2012
>>>
>>> This seems overly aggressive to me. Why not start by baselining at
>>> VC++ 2010, and bump up everything else to match?
>>
>> IIRC the only significant difference among VS 2012 and VS 2010 is range
>> for loops.
>
> Which is really sad, given how nice they are, but I think it would be huge
progress to move LLVM 3.4 to require the VS 2010 feature set (and the
corresponding GCC/clang/etc versions).  We can move up to VS 2012 as a second
step and second discussion.
I may be remembering incorrectly, but I thought we already supported
only VS2010 and higher today.  AFAIK, there are no 2008 build bots as
part of the process, and I've not seen a 2008-specific patch for
compatibility in ages.

~Aaron

On Sun, Oct 27, 2013 at 11:18 AM, Chris Lattner <clattner at apple.com>
wrote:
> On Sun, Oct 27, 2013 at 2:23 AM, Chandler Carruth <chandlerc at
google.com>
> wrote:> Concrete long term proposal:
> >
> > We support building with C++ toolchains which were released and widely
> available on their respective target platforms at least 2 years prior to
> the next 6-month-cycle release. Immediately after each branch of a release,
> mainline can move the bar forward by 6 months. Thus, each release should
> build with the four previous releases.
>
> I don't think it makes sense to have a hard policy like this.  It is
fine
> to have a goal that allows us to continue picking up new features over
> time, but I think each such change will have to be discussed (at length)
> with the specifics of which interesting host configurations we would be
> dropping.
>
I didn't really intend to indicate this would be a hard policy, more that
it would be the guideline. Part of the idea is that after each release
branch is cut we could evaluate what a reasonable baseline would look like.

I do think that 2 years is a good guideline, in part because two of the
three toolchains which impact us most already use time-driven release
cycles.

My hope is that we could *strive* for no more than two years of support for
older toolchains as a way to push ourselves to not let this slip.


An obvious other input to this decision would be exactly what Benjamin
brought up: we should look at what toolchain versions various OSes are
shipping with. However, I think the diversity of OS is too broad to be
easily explained in our getting started docs, etc. I would rather use the
OS situation to inform the particular versions of each toolchain that we
try to support, but to word the decision in terms of the toolchain versions.

> One short term caveat: Windows is special.
>
> I don't see how it is special.  We should just look at all of the
> compilers we need to support, and factor that set in.  We should continue
> to increment the baseline compilers over time, but a global "two year
old
> compilers only" policy doesn't make sense to me.  I also think
that windows
> will be the lowest bar anyway.
>
See above. I'm not interested in a hard policy. I think MSVC will end up
being special because we may realistically want a *narrower* set of
toolchains supported there given both the rapid advances of MSVC in the
last year, and the rapid changes to Clang and LLVM's role on that platform.

(And note, I misspoke previously, clearly MinGW is just GCC, I'm talking
about MSVC here)
> Now for the carrot: if we go with this plan, then immediately after
> branching for 3.4,  we would be able to use the vast majority of C++11
> features, targeting the following as the oldest toolchains supported
> through the 3.5 release timeframe:
> >
> > GCC 4.7
> > Clang 3.1
> > VS 2012
>
> This seems overly aggressive to me.  Why not start by baselining at VC++
> 2010, and bump up everything else to match?  That would give us some basic
> C++'11 features for 3.4, then we could bump it up to VS 2012 in 3.5 if
that
> goes well.
>
As others have pointed out, our baseline is already VS 2010, but our C++11
features have been held back by concern over GCC. I think the time frame is
right to jump all the way to GCC 4.7 as the target for our 3.5 release, and
would like to bump VS to 2012 at the same time if at all possible.

This isn't just a bump either, it brings things that I think will be very
useful:
- Fixed semantics for r-value references that is relevant to using move
semantics broadly in LLVM
- Range-based for loops, because as much as people say it "just reduces
boiler plate", omg it is so much nicer
- better concurrency support, notably we may be able to use the standard
atomics library (with some testing and restrictions) which have compiler
assistance behind them.
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On Sun, Oct 27, 2013 at 11:30 AM, Joerg Sonnenberger <
joerg at britannica.bec.de> wrote:
> > > Some notable features we would get to use:
> > >
> > > - r-value references, move semantics, etc
> > > - auto
> > > - range for loops
> > > - lambdas
> > > - static_assert
> > > - nullptr
> > > - std::unique_ptr, std::tuple, some other nice library stuff
>
> It would be nice to keep the list to things that don't require too much
> support from the STL implementation. Locale support and std::thread in
> the various forms are a real show stopper for bootstrapping otherwise.

Strong agreement. I think the most interesting would be the parts that need
compiler assistance, such as type traits and atomics. Even then, the nice
thing about the library is that we can easily test out the waters, and
supplement with our own libraries as needed. We have a harder time of that
with language features.
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On 27.10.2013, at 20:07, Óscar Fuentes <ofv at wanadoo.es> wrote:
> Chris Lattner <clattner at apple.com> writes:
> 
>>> One short term caveat: Windows is special.
> 
> s/Windows/Visual Studio.
> 
> MinGW has the latest and greatest gcc.
> 
>> I don't see how it is special.
> 
> It is special, sadly, and I'm not talking about C++11 support only, but
> about the policies MS follows which too often makes very inconvenient
> (or even impossible) to upgrade to newer VS versions. The latest example
> that comes to mind was the release of VS2012: they removed Windows XP
> support, as if upgrading the OS is a non-issue if you ask for it to your
> users on a polite tone. An uproar followed and they backpedaled on a
> service pack some months later, but that not always happens.
I might be mistaken, but to compile for WinXP on VS 2012 you have to switch the
Platform Toolset and AFAICT that means it will essentially be using the VS 2010
compiler and libraries. So when it comes to using newer C++ functionality you
will still be stuck on the VS 2010 level even if you are using VS 2012 and if
you are using any VS2012 improvements you will not be able to compile for XP.

Basically (again: AFAICT): if you want clang to be compiled for WinXP using VS,
the C++ features of VS 2010 are a hard limit and that will not change.

Dix

On 10/28/13 11:45 AM, Dix Lorenz wrote:
> On 27.10.2013, at 20:07, Óscar Fuentes <ofv at wanadoo.es> wrote:
>
>> Chris Lattner <clattner at apple.com> writes:
>>
>>>> One short term caveat: Windows is special.
>> s/Windows/Visual Studio.
>>
>> MinGW has the latest and greatest gcc.
>>
>>> I don't see how it is special.
>> It is special, sadly, and I'm not talking about C++11 support only,
but
>> about the policies MS follows which too often makes very inconvenient
>> (or even impossible) to upgrade to newer VS versions. The latest
example
>> that comes to mind was the release of VS2012: they removed Windows XP
>> support, as if upgrading the OS is a non-issue if you ask for it to
your
>> users on a polite tone. An uproar followed and they backpedaled on a
>> service pack some months later, but that not always happens.
> I might be mistaken, but to compile for WinXP on VS 2012 you have to switch
the Platform Toolset and AFAICT that means it will essentially be using the VS
2010 compiler and libraries. So when it comes to using newer C++ functionality
you will still be stuck on the VS 2010 level even if you are using VS 2012 and
if you are using any VS2012 improvements you will not be able to compile for XP.
>
> Basically (again: AFAICT): if you want clang to be compiled for WinXP using
VS, the C++ features of VS 2010 are a hard limit and that will not change.
XP mainstream support is already EOL and extended support is  April 2014
http://windows.microsoft.com/en-us/windows/products/lifecycle

I can guess it may get extended, but imho it seems unreasonable to hold 
up clang based on a non-supported product. (Yes the reality is many many 
people will continue to use it, but....)

Wasn't VS 2012 express the 1st to ship a free 64bit C++ compiler?
--------
My vote would be 2012+ and drop 2010

On Mon, Oct 28, 2013 at 9:00 AM, Óscar Fuentes <ofv at wanadoo.es> wrote:
> Dix Lorenz <lists at dix-lorenz.de> writes:
>
> > I might be mistaken, but to compile for WinXP on VS 2012 you have to
> > switch the Platform Toolset and AFAICT that means it will essentially
> > be using the VS 2010 compiler and libraries.
>
> That was how VS 2012 worked at release time. On Update 1 they added
> support for building Windows XP applications with the VS 2012 compiler.
>
> VS 2013 C++ compiler can build XP applications too.
>
So this complexity highlights to me one important thing: whatever group of
MSVC tools are
selected as the baseline, it would be really helpful to have people
knowledgeable
about that contribute to the description of precisely which C++11
constructs are
allowed (and if there are any surprising cases which don't work), for those
of us
who have no idea precisely what will get past an MSVC compiler and no means
or desire to set up a Windows system just for testing. It's very
frustrating when
development turns in to a "I checked on all my systems, checked in and get
complaints from people on very different systems whose build broke"
experience.
(Yeah, I know there's any irony there...) Getting a clearly delimited
feature list
should help reduce that.

Cheers,
Dave

-- 
cheers, dave tweed__________________________
high-performance computing and machine vision expert: david.tweed at gmail.com
"while having code so boring anyone can maintain it, use Python." --
attempted insult seen on slashdot
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On Mon, Oct 28, 2013 at 2:18 AM, David Tweed <david.tweed at gmail.com>
wrote:
> On Mon, Oct 28, 2013 at 9:00 AM, Óscar Fuentes <ofv at wanadoo.es>
wrote:
>
>> Dix Lorenz <lists at dix-lorenz.de> writes:
>>
>> > I might be mistaken, but to compile for WinXP on VS 2012 you have
to
>> > switch the Platform Toolset and AFAICT that means it will
essentially
>> > be using the VS 2010 compiler and libraries.
>>
>> That was how VS 2012 worked at release time. On Update 1 they added
>> support for building Windows XP applications with the VS 2012 compiler.
>>
>> VS 2013 C++ compiler can build XP applications too.
>>
>
> So this complexity highlights to me one important thing: whatever group of
> MSVC tools are
> selected as the baseline, it would be really helpful to have people
> knowledgeable
> about that contribute to the description of precisely which C++11
> constructs are
> allowed (and if there are any surprising cases which don't work), for
> those of us
> who have no idea precisely what will get past an MSVC compiler and no means
> or desire to set up a Windows system just for testing. It's very
> frustrating when
> development turns in to a "I checked on all my systems, checked in and
get
> complaints from people on very different systems whose build broke"
> experience.
> (Yeah, I know there's any irony there...) Getting a clearly delimited
> feature list
> should help reduce that.
>
Fortunately, we have a bunch of really active contributors working closely
with Visual Studio. =] I'm very confident that between Reid, Warren, Hans,
Rui, Michael, Anton, and others we can figure out clear and well understood
guidelines.

Naturally, building with Visual Studio will be the final test. We have
build bots and a lot of active developers so I don't think we'll lose
sight
of this.
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Here is a table detailing C++11 features support for Visual C++ 2010, 2012,
2013

http://msdn.microsoft.com/en-us/library/vstudio/hh567368.aspx

Specifically, range-based for loops are supported in Visual C++ 2012, 2013
but not in 2010.

Yaron



2013/10/28 David Tweed <david.tweed at gmail.com>
> On Mon, Oct 28, 2013 at 9:00 AM, Óscar Fuentes <ofv at wanadoo.es>
wrote:
>
>> Dix Lorenz <lists at dix-lorenz.de> writes:
>>
>> > I might be mistaken, but to compile for WinXP on VS 2012 you have
to
>> > switch the Platform Toolset and AFAICT that means it will
essentially
>> > be using the VS 2010 compiler and libraries.
>>
>> That was how VS 2012 worked at release time. On Update 1 they added
>> support for building Windows XP applications with the VS 2012 compiler.
>>
>> VS 2013 C++ compiler can build XP applications too.
>>
>
> So this complexity highlights to me one important thing: whatever group of
> MSVC tools are
> selected as the baseline, it would be really helpful to have people
> knowledgeable
> about that contribute to the description of precisely which C++11
> constructs are
> allowed (and if there are any surprising cases which don't work), for
> those of us
> who have no idea precisely what will get past an MSVC compiler and no means
> or desire to set up a Windows system just for testing. It's very
> frustrating when
> development turns in to a "I checked on all my systems, checked in and
get
> complaints from people on very different systems whose build broke"
> experience.
> (Yeah, I know there's any irony there...) Getting a clearly delimited
> feature list
> should help reduce that.
>
> Cheers,
> Dave
>
> --
> cheers, dave tweed__________________________
> high-performance computing and machine vision expert:
> david.tweed at gmail.com
> "while having code so boring anyone can maintain it, use Python."
--
> attempted insult seen on slashdot
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
>
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+1 this. Get the build bots setup first on whatever versions are decided on
before making the jump.
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu]
> On Behalf Of Rafael Espíndola
> Sent: Sunday, October 27, 2013 5:34 AM
> To: Chandler Carruth
> Cc: clang-dev Developers; LLVM Developers Mailing List
> Subject: Re: [LLVMdev] [cfe-dev] RFC: A proposal to move toward using
> C++11 features in LLVM & Clang / bounding support for old host
compilers
> 
> >> GCC 4.7
> >> Clang 3.1
> >> VS 2012
> 
> Xcode 4.2's clang?
> 
> Do we already have bots with all these versions?
> 
> Cheers,
> Rafael
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On 28 Oct 2013, at 04:45, Dix Lorenz <lists at dix-lorenz.de>
wrote:
> 
> I might be mistaken, but to compile for WinXP on VS 2012 you have to switch
the Platform Toolset and AFAICT that means it will essentially be using the VS
2010 compiler and libraries. So when it comes to using newer C++ functionality
you will still be stuck on the VS 2010 level even if you are using VS 2012 and
if you are using any VS2012 improvements you will not be able to compile for XP.
> 
> Basically (again: AFAICT): if you want clang to be compiled for WinXP using
VS, the C++ features of VS 2010 are a hard limit and that will not change.
> 
> Dix
>From http://msdn.microsoft.com/en-us/library/vstudio/jj851139.aspx:
"The Visual Studio 2012 - Windows XP (v110_xp) platform toolset that's
included in Visual Studio 2012 Update 1 is a version of the Windows 7 SDK that
was included in Visual Studio 2010, but it uses the Visual Studio 2012 C++
compiler”

As such all the C++11 language features of VS 2012 are, AFAIK, available when
targeting XP.

>> It is special, sadly, and I'm not talking about C++11 support only,
but
>> about the policies MS follows which too often makes very inconvenient
>> (or even impossible) to upgrade to newer VS versions. The latest
example
>> that comes to mind was the release of VS2012: they removed Windows XP
>> support, as if upgrading the OS is a non-issue if you ask for it to
your
>> users on a polite tone. An uproar followed and they backpedaled on a
>> service pack some months later, but that not always happens.
>
> I might be mistaken, but to compile for WinXP on VS 2012 you have to switch
the Platform Toolset and AFAICT that means it will essentially be using the VS
2010 compiler and libraries. So when it comes to using newer C++ functionality
you will still be stuck on the VS 2010 level even if you are using VS 2012 and
if you are using any VS2012 improvements you will not be able to compile for XP.
>
> Basically (again: AFAICT): if you want clang to be compiled for WinXP using
VS, the C++ features of VS 2010 are a hard limit and that will not change.
A different issue than what VS 2012 can _target_, is what VS 2012 can
_run on_: it cannot run on Windows XP.

Say what you want about how old Windows XP is and how close it is to
being end-of-life'd by Microsoft, at the end of the day it still
commands one third (!) of all desktop operating system market share [1].

So, by dropping support for VS 2010, you will be making any developer
who uses Windows XP - potentially a large number of developers given
Windows XP's still huge market share - unable to build clang.

Regards,
Nate

[1]
http://www.netmarketshare.com/operating-system-market-share.aspx?qprid=10&qpcustomd=0