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Neil Nelson via llvm-dev

2020-Apr-04 19:48 UTC

[llvm-dev] Upgrading LLVM's minimum required CMake version

'Supported' means that it comes from the packages available from the 
distribution that can be seen via this page.

https://packages.ubuntu.com/

These packages have been processed by the Ubuntu community to obtain a 
reliability expectation that would not apply, for example, to a PPA.

The difference between installing or building Clang and LLVM from 
original sources as against installing versions available from the 
distribution when compared to doing the same with cmake, is that the 
user accepts the inherent risks from Clang and LLVM, but Clang and LLVM 
can not accept the risks from the cmake group and then expect the user 
to merely assume that there are no additional risks from installing cmake.

The distributions are not merely just collections of software, they are 
collections of software that have some guarantee of working well 
together and without bugs and other issues because they have been used 
and tested by that use in the distribution community.

The importance of this distinction between the quality of software 
expected in a distribution as against installing directly from source is 
apparently lost on those who did not live through the pre-distribution 
days. During that time we had to gather up the dependencies ourselves, 
trying to get the correct versions, hoping that the software compiled 
and worked with the other dependencies, and hope we did not install 
malware and hackware. And quite often it was a futile attempt to gather 
together software dependencies of any size.

Those who lived through that time remember it as the dark-ages of long 
ago, never to be seen again.

Neil Nelson

On 4/4/20 11:48 AM, Mehdi AMINI via llvm-dev wrote:>
>
> On Thu, Apr 2, 2020 at 10:49 AM Shoaib Meenai via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>
>     I’m in favor of all this. Thanks for volunteering! I’m happy to
>     help out in whatever way.
>
>     Some things it might be worth figuring out for future upgrades:
>
>     * If we want to limit ourselves to CMake versions supported by LTS
>     releases of distros, which distros should we consider, and how far
>     back should we go (i.e. is it just the latest LTS or the last two
>     LTS versions)?
>
>
> Can you clarify what "supported" means? Does it include PPA on
ubuntu
> for example?
> I wouldn't limit ourselves artificially to the version of CMake 
> "natively" available on an OS in cases where we already requires
a
> more recent compiler than the default one available: if we consider OK 
> to require as user to build clang or gcc from source or use a PPA, we 
> should be OK the same way with CMake.
>
>
>     * For platforms like Ubuntu where CMake publishes its own packages
>     (that you can install via the platform’s package manager), do
>     those count, or do we only consider the CMake that comes in the OS
>     packages?
>
>     * Do we have any limitations around how often/when we upgrade?
>     You’re tying the upgrade to after the branch, which is pretty
>     standard, but e.g. if we wanted to upgrade to 3.8.0 now and then
>     upgrade to 3.13.4 after the branch, would people be okay with
>     that, or should we limit upgrades to just shortly after a branch?
>
>     *From: *<ldionne at apple.com <mailto:ldionne at
apple.com>> on behalf
>     of Louis Dionne <ldionne at apple.com <mailto:ldionne at
apple.com>>
>     *Date: *Thursday, April 2, 2020 at 7:20 AM
>     *To: *Shoaib Meenai <smeenai at fb.com <mailto:smeenai at
fb.com>>
>     *Cc: *"llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>"
>     <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>>, Chris
>     Bieneman <beanz at apple.com <mailto:beanz at apple.com>>,
Petr Hosek
>     <phosek at chromium.org <mailto:phosek at chromium.org>>,
Saleem
>     Abdulrasool <compnerd at compnerd.org
>     <mailto:compnerd at compnerd.org>>, "tstellar at
redhat.com
>     <mailto:tstellar at redhat.com>" <tstellar at redhat.com
>     <mailto:tstellar at redhat.com>>
>     *Subject: *Re: Upgrading LLVM's minimum required CMake version
>
>     Okay, so we've had some discussion on this thread, and although
>     some people (including me) would like a more aggressive policy, I
>     believe the following will not get any objection (based on the
>     thread). On April 23rd 2020, Ubuntu 20.04 LTS will ship with CMake
>     3.16.x. This will make the lower bound for LTS distributions be
>     3.13.4, and so I suggest we upgrade to that. Here's a proposed
>     process:
>
>     1. Immediately add a CMake warning in <root>/llvm/CMakeLists.txt
>     saying that CMake 3.13.4 will be the new minimum version starting
>     with LLVM 12.0.0, and mentioning the versions used in various LTSes.
>
>     2. Immediately send a courtesy heads-up email to all build-bot
>     owners telling them about the upcoming change.
>
>     3. Right after we branch off the release branch for LLVM 11.0.0
>     (the next one), make the minimum CMake version required be 3.13.4.
>
>     4. Iterate on (3) until all bots are migrated.
>
>     5. Send a message to the list saying the bump is complete. At that
>     time, projects are free to start using features from 3.13.4.
>
>     Unless someone else absolutely wants to bite the bullet, I
>     volunteer to do the above steps.
>
>     Thoughts?
>
>     Louis
>
>         On Mar 26, 2020, at 16:07, Shoaib Meenai <smeenai at fb.com
>         <mailto:smeenai at fb.com>> wrote:
>
>         We had this discussion a few months ago and it petered out,
>         and it’s recently been revived in the context of upgrading the
>         CMake version specifically for libc++ (at which point people
>         suggested upgrading the CMake version used by all of LLVM), so
>         let’s try to move this forward.
>
>         Our current required minimum version is CMake 3.4.3, which was
>         released on January 25th 2016. It’s interesting to note that
>         LLVM started requiring 3.4.3 on May 31st 2016, which was just
>         4 months after its release.
>
>         Let’s look at the CMake versions available on various distros
>         and operating systems. I’m unfamiliar with many of these, so I
>         apologize if I get something wrong. (I’m using pkgs.org
>        
<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
>         for most of this information.)
>         * RHEL 6 (released Nov 10th 2010) : 3.6.1 (via EPEL)
>         * RHEL 7 (released June 10th 2014): 3.14.7 (via EPEL)
>         * RHEL 8 (released May 7th 2019): 3.11.4 (maybe pkgs.org
>        
<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
>         is screwy on this one, because it doesn’t make sense that RHEL
>         7 should have a newer available version than RHEL 8)
>         * Debian 9 (released June 17th 2017): 3.7.2
>         * Debian 10 (released July 6th 2019): 3.13.4
>         * Ubuntu 16.04 LTS (released April 21st 2016): 3.5.1
>         * Ubuntu 18.04 LTS (released April 26th 2018): 3.10.2
>         * FreeBSD 11 (released October 10th 2016): 3.15.5 (presumably
>         upgraded in a point release)
>         * FreeBSD 12 (released December 11th 2018): 3.15.5 (presumably
>         upgraded in a point release)
>         * NetBSD 8.1 (released May 31st 2019): 3.16.1
>         * NetBSD 9.0 (released February 14th 2020): 3.16.1
>         * OpenBSD: couldn’t find the version
>         * macOS: latest version is readily available through Homebrew
>         * Windows: You can install it yourself or use the one bundled
>         with Visual Studio. I don't know what versions are bundled
>         with Visual Studio; some searching suggests Visual Studio 2017
>         has CMake 3.12 and Visual Studio 2019 has 3.15, though I have
>         no confirmation of that.
>
>         Note that CMake provides prebuilt binaries for Linux, macOS,
>         and Windows, and it’s also straightforward to build from
>         source (it has very conservative compiler requirements). One
>         suggestion that was brought up in the past was for LLVM’s
>         build system to just download a newer version of CMake if you
>         attempted to build it using one that was too old, but there
>         was opposition [1]. There was also a suggestion to have a
>         script in LLVM to download and build CMake for you, but there
>         were mixed opinions on this too [2], particularly since many
>         developers might prefer downloading a binary release to
>         building from source themselves (though of course the script
>         could also download binary releases if applicable). I
>         personally think downloading or building CMake yourself isn’t
>         a high barrier for anyone wanting to build LLVM (and in
>         particular it’s *much* more straightforward than building LLVM
>         itself), but I can understand why people would prefer to stick
>         to versions available in distros.
>
>         Another suggestion that came up last time was to set a policy
>         for upgrading CMake versions on some regular basis. The
>         opposition to this was that we should upgrade CMake versions
>         only when a newer version has a compelling enough feature to
>         justify upgrading, rather than always upgrading. I can see
>         arguments for both approaches, but we should definitely at
>         least think about the benefits we can get from upgrading
>         versions. I've gone through the CMake release notes and
>         highlighted features which seemed potentially valuable for
>         LLVM. Note that I'm only highlighting features for which our
>         minimum CMake version would have to be bumped up in order for
>         our build system to take advantage of. There are other useful
>         features in newer CMake versions, but you can take advantage
>         of them just by using a newer CMake yourself. For example, 3.9
>         loosens the dependencies of object compilation, which should
>         result in faster Ninja builds.
>
>         CMake 3.5 (released March 8th 2016):
>         * install(DIRECTORY) supports generator expressions
>
>         CMake 3.6 (released July 7th 2016):
>         * install() supports EXCLUDE_FROM_ALL
>         * list() supports FILTER to filter by regular expression
>         * Subninja support, which could theoretically be used for much
>         faster runtimes builds, although in practice we probably want
>         to make ExternalProject support this directly instead of
>         trying to layer our own meta-build system on top
>         * CMAKE_TRY_COMPILE_TARGET_TYPE to tell try_compile to build a
>         static library instead of an executable, which will greatly
>         simplify the compiler-rt build
>
>         CMake 3.7 (released November 11th 2016):
>         * New if() comparison operators LESS_EQUAL, GREATER_EQUAL,
>         STRLESS_EQUAL, STRGREATER_EQUAL, VERSION_LESS_EQUAL, and
>         VERSION_GREATER_EQUAL
>
>         CMake 3.8 (released April 10th 2017):
>         * Compile features for C++17, which is required to build
>         libc++ correctly
>         * Support for compile features for specific C++ features
>         instead of only being able to specify standard versions
>         * rpath support via BUILD_RPATH target property and
>         CMAKE_BUILD_RPATH variable
>         * Apple framework support for static libraries
>         * New swig_add_library command in the UseSWIG module
>         * New generator expression $<IF:cond,true-value,false-value>
>
>         CMake 3.9 (released July 18th 2017):
>         * install(TARGETS) and install(EXPORTS) support for object
>         libraries, which will simplify the compiler-rt build
>         * TARGET_OBJECTS generator expression support in
>         add_custom_command and file(GENERATE)
>         * $<TARGET_BUNDLE_DIR:tgt> and
>         $<TARGET_BUNDLE_CONTENT_DIR:tgt> generator expressions for
>         Apple bundles
>
>         CMake 3.10 (released November 20th 2017):
>         * include_guard() command for proper guarding against double
>         includes of CMake scripts
>         * An interesting aside is that this is the first verion of
>         CMake to require C++11 to build, which should give a good
>         sense of how conservative they are about compiler requirements
>
>         CMake 3.11 (released March 28th 2018):
>         * add_library() and add_executable() can be called without
>         sources as long as target_sources() is used later
>         * target_compile_{definitions,features,options},
>         target_include_directories(), target_sources(), and
>         target_link_libraries() can set the corresponding INTERFACE_*
>         properties on imported targets
>         * COMPILE_DEFINITIONS supports generator expressions
>         * COMPILE_OPTIONS source file property added
>         * INCLUDE_DIRECTORIES source file property added
>         * Interface libraries support custom properites
>
>         CMake 3.12 (released July 17th 2018):
>         * add_compile_definitions() added to add compile definitions
>         for targets (to avoid the global pollution caused by
>         add_definitions())
>         * cmake_minimum_required() supports a version range to
>         indicate tested CMake versions and set policies accordingly
>         * file(TOUCH) and file(TOUCH_NOCREATE) added
>         * list(JOIN), list(SUBLIST) and list(TRANSFORM) added
>         * string(JOIN) added
>         * SHELL: prefix support in target_compile_options to avoid
>         errant deduplication
>         * target_link_libraries() supports object libraries and
>         propagates usage requirements
>         * EXPORT_PROPERTIES target property to control the target
>         properties exported by export() and install(EXPORT)
>         * FindLibXml2 provides imported targets
>         * New FindPython, FindPython2, and FindPython3 modules to ease
>         location Python and selecting a specific version
>         * Modernization of UseSWIG module
>         * New generator expressions $<GENEX_EVAL:...>,
>         $<TARGET_GENEX_EVAL:target,...>, $<IN_LIST:...>,
>         $<TARGET_EXISTS:...> and $<TARGET_NAME_IF_EXISTS:...>
>         * Compile features support for C++20
>
>         CMake 3.13 (released November 20th 2018):
>         * cmake -E create_symlink supported on Windows
>         * target_link_directories() and target_link_options() commands
>         to set link options instead of awkwardly having to use
>         target_link_libraries() for this purpose
>         * UseSWIG can manage INCLUDE_DIRECTORIES for SWIG compilation
>
>         CMake 3.14 (released March 14th 2019):
>         * file(CREATE_LINK) to create hard or symbolic links
>         * if(DEFINED CACHE{VAR}) for checking if a cache variable is
>         defined
>         * $<IN_LIST:...> generator expression correctly handles empty
>         argument
>         * Fixes for object library linking propagation
>         * Link options to manage position independent executables
>         added automatically
>
>         CMake 3.15 (released July 17th 2019):
>         * list(PREPEND), list(POP_FRONT) and list(POP_BACK) added
>         * New message() types NOTICE, VERBOSE, DEBUG and TRACE
>         * string(REPEAT) added
>         * MSVC_RUNTIME_LIBRARY target property and
>         CMAKE_MSVC_RUNTIME_LIBRARY variable to select the runtime
>         library type for MSVC
>         * $<C_COMPILER_ID:...>, $<CXX_COMPILER_ID:...>,
>         $<COMPILE_LANGUAGE:...>, and $<PLATFORM_ID:...>
generator
>         expressions support matching one value from a list
>         * $<COMPILE_LANG_AND_ID:...> generator expression added
>         * $<FILTER:list,INCLUDE|EXCLUDE,regex> generator expression
added
>         * $<REMOVE_DUPLICATES:list> generator expression added
>         * New $<TARGET_FILE*> generator expressions added:
>         $<TARGET_FILE_PREFIX:...>,
$<TARGET_FILE_BASE_NAME:...>,
>         $<TARGET_FILE_SUFFIX:...>,
$<TARGET_LINKER_FILE_PREFIX:...>,
>         $<TARGET_LINKER_FILE_BASE_NAME:...>,
>         $<TARGET_LINKER_FILE_SUFFIX:...>,
$<TARGET_PDB_FILE_BASE_NAME:...>
>         * $<TARGET_OBJECTS:...> generator expression supports
>         executables and static, shared, and module libraries
>
>         CMake 3.16 (released November 26th 2019):
>         * Support for generator expressions in BUILD_RPATH and
>         INSTALL_RPATH
>
>         CMake 3.17 (released March 20th 2020):
>         * Ninja Multi-Config generator, which among other things would
>         greatly simplify LLVM_OPTIMIZED_TABLEGEN
>         * foreach(ZIP_LISTS) added to iterate multiple lists
>         simultaneously
>         * New message() keywords CHECK_START, CHECK_PASS, and CHECK_FAIL
>         * INSTALL_NAME_DIR supports generator expressions
>
>         Our build system is incredibly complex, and many of these
>         features can be used to clean it up and make it much more
>         maintainable. I would personally like us to at least bump up
>         to CMake 3.12. I also do think it's worth establishing a
>         policy and process around upgrading CMake versions, since
>         newer versions keep on adding useful features (particularly
>         better generator expression support), and we want to be able
>         to keep taking advantage of them.
>
>         [1]
>         http://lists.llvm.org/pipermail/llvm-dev/2019-November/136485.html
>        
<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136485.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=HtGj57-MndDqyK71vXRwheQXms3WKx9rT-8WAVyTB3c&e=>
>
>         [2]
>         http://lists.llvm.org/pipermail/llvm-dev/2019-November/136488.html
>        
<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136488.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=hHrZYrGk0WStJ3TjjIsXg2NMvVUP-f4woTFtaFlYkG8&e=>
>
>
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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Mehdi AMINI via llvm-dev

2020-Apr-04 21:11 UTC

head link

[llvm-dev] Upgrading LLVM's minimum required CMake version

On Sat, Apr 4, 2020 at 12:48 PM Neil Nelson via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> 'Supported' means that it comes from the packages available from
the
> distribution that can be seen via this page.
>
> https://packages.ubuntu.com/
>
> These packages have been processed by the Ubuntu community to obtain a
> reliability expectation that would not apply, for example, to a PPA.
>
Right, so I'm looking for an answer to my question, I'll try make it
more
concrete what I mean by "in cases where we already requires a more recent
compiler than the default one available".
If I take Xenial for instance, the most recent GCC version is 5.4.0 as far
as I can tell: https://packages.ubuntu.com/xenial/devel/gcc-5 ; assuming
LLVM would move at some point to require a more recent version than 5.4, it
would mean that you couldn't build LLVM with the packages available on
Xenial. In this situation (which I referred to as "cases where we already
requires a more recent compiler than the default one available") we already
expect the user to get a toolchain from a non-primary package source on
this distribution, and if we do this for the toolchain already I would
expect that we should be able to do it as well for CMake (again: for a
given distribution/version).

> The difference between installing or building Clang and LLVM from original
> sources as against installing versions available from the distribution
>I don't understand this sentence?

> when compared to doing the same with cmake, is that the user accepts the
> inherent risks from Clang and LLVM, but Clang and LLVM can not accept the
> risks from the cmake group and then expect the user to merely assume that
> there are no additional risks from installing cmake.
>Maybe a nit here, but there is no need to *install* CMake: it could be
trivially build in the build directory. We are talking about a trivial step
here:

# Inside llvm-project/
$ mkdir build/ && cd build/
# bootstrap CMake
$ wget
https://github.com/Kitware/CMake/releases/download/v3.17.0/cmake-3.17.0.tar.gz
$ echo "b74c05b55115eacc4fa2b77a814981dbda05cdc95a53e279fe16b7b272f00847
 cmake-3.17.0.tar.gz" | sha256sum -c
$ tar -xf cmake-3.17.0.tar.gz && cd cmake-3.17.0 && ./bootstrap
&& make
# Done, cmake is usable, *nothing* is installed on the user system,
everything is self-contained *inside* the build directory itself.
$ ./cmake-3.17.0/bin/cmake ../llvm/ -D.... # build LLVM as usual.



> The distributions are not merely just collections of software, they are
> collections of software that have some guarantee of working well together
> and without bugs and other issues because they have been used and tested by
> that use in the distribution community.
>
> The importance of this distinction between the quality of software
> expected in a distribution as against installing directly from source is
> apparently lost on those who did not live through the pre-distribution
> days. During that time we had to gather up the dependencies ourselves,
> trying to get the correct versions, hoping that the software compiled and
> worked with the other dependencies, and hope we did not install malware and
> hackware. And quite often it was a futile attempt to gather together
> software dependencies of any size.
>
> Those who lived through that time remember it as the dark-ages of long
> ago, never to be seen again.
>Been there, done that... (actually suffered from that).

I claim this is just not the same situation here: CMake is a self-contained
dependencies and as shown above does not need to escape anywhere outside
the build directory.

-- 
Mehdi


> On 4/4/20 11:48 AM, Mehdi AMINI via llvm-dev wrote:
>
>
>
> On Thu, Apr 2, 2020 at 10:49 AM Shoaib Meenai via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I’m in favor of all this. Thanks for volunteering! I’m happy to help
out
>> in whatever way.
>>
>>
>>
>> Some things it might be worth figuring out for future upgrades:
>>
>> * If we want to limit ourselves to CMake versions supported by LTS
>> releases of distros, which distros should we consider, and how far back
>> should we go (i.e. is it just the latest LTS or the last two LTS
versions)?
>>
>
> Can you clarify what "supported" means? Does it include PPA on
ubuntu for
> example?
> I wouldn't limit ourselves artificially to the version of CMake
"natively"
> available on an OS in cases where we already requires a more recent
> compiler than the default one available: if we consider OK to require as
> user to build clang or gcc from source or use a PPA, we should be OK the
> same way with CMake.
>
>
>
>> * For platforms like Ubuntu where CMake publishes its own packages
(that
>> you can install via the platform’s package manager), do those count, or
do
>> we only consider the CMake that comes in the OS packages?
>>
>> * Do we have any limitations around how often/when we upgrade? You’re
>> tying the upgrade to after the branch, which is pretty standard, but
e.g.
>> if we wanted to upgrade to 3.8.0 now and then upgrade to 3.13.4 after
the
>> branch, would people be okay with that, or should we limit upgrades to
just
>> shortly after a branch?
>>
>>
>>
>> *From: *<ldionne at apple.com> on behalf of Louis Dionne
<ldionne at apple.com>
>> *Date: *Thursday, April 2, 2020 at 7:20 AM
>> *To: *Shoaib Meenai <smeenai at fb.com>
>> *Cc: *"llvm-dev at lists.llvm.org" <llvm-dev at
lists.llvm.org>, Chris
>> Bieneman <beanz at apple.com>, Petr Hosek <phosek at
chromium.org>, Saleem
>> Abdulrasool <compnerd at compnerd.org>, "tstellar at
redhat.com" <
>> tstellar at redhat.com>
>> *Subject: *Re: Upgrading LLVM's minimum required CMake version
>>
>>
>>
>> Okay, so we've had some discussion on this thread, and although
some
>> people (including me) would like a more aggressive policy, I believe
the
>> following will not get any objection (based on the thread). On April
23rd
>> 2020, Ubuntu 20.04 LTS will ship with CMake 3.16.x. This will make the
>> lower bound for LTS distributions be 3.13.4, and so I suggest we
upgrade to
>> that. Here's a proposed process:
>>
>>
>>
>> 1. Immediately add a CMake warning in <root>/llvm/CMakeLists.txt
saying
>> that CMake 3.13.4 will be the new minimum version starting with LLVM
>> 12.0.0, and mentioning the versions used in various LTSes.
>>
>> 2. Immediately send a courtesy heads-up email to all build-bot owners
>> telling them about the upcoming change.
>>
>> 3. Right after we branch off the release branch for LLVM 11.0.0 (the
next
>> one), make the minimum CMake version required be 3.13.4.
>>
>> 4. Iterate on (3) until all bots are migrated.
>>
>> 5. Send a message to the list saying the bump is complete. At that
time,
>> projects are free to start using features from 3.13.4.
>>
>>
>>
>> Unless someone else absolutely wants to bite the bullet, I volunteer to
>> do the above steps.
>>
>>
>>
>> Thoughts?
>>
>>
>>
>> Louis
>>
>>
>>
>>
>>
>> On Mar 26, 2020, at 16:07, Shoaib Meenai <smeenai at fb.com>
wrote:
>>
>>
>>
>> We had this discussion a few months ago and it petered out, and it’s
>> recently been revived in the context of upgrading the CMake version
>> specifically for libc++ (at which point people suggested upgrading the
>> CMake version used by all of LLVM), so let’s try to move this forward.
>>
>> Our current required minimum version is CMake 3.4.3, which was released
>> on January 25th 2016. It’s interesting to note that LLVM started
requiring
>> 3.4.3 on May 31st 2016, which was just 4 months after its release.
>>
>> Let’s look at the CMake versions available on various distros and
>> operating systems. I’m unfamiliar with many of these, so I apologize if
I
>> get something wrong. (I’m using pkgs.org
>>
<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
>> for most of this information.)
>> * RHEL 6 (released Nov 10th 2010) : 3.6.1 (via EPEL)
>> * RHEL 7 (released June 10th 2014): 3.14.7 (via EPEL)
>> * RHEL 8 (released May 7th 2019): 3.11.4 (maybe pkgs.org
>>
<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
>> is screwy on this one, because it doesn’t make sense that RHEL 7 should
>> have a newer available version than RHEL 8)
>> * Debian 9 (released June 17th 2017): 3.7.2
>> * Debian 10 (released July 6th 2019): 3.13.4
>> * Ubuntu 16.04 LTS (released April 21st 2016): 3.5.1
>> * Ubuntu 18.04 LTS (released April 26th 2018): 3.10.2
>> * FreeBSD 11 (released October 10th 2016): 3.15.5 (presumably upgraded
in
>> a point release)
>> * FreeBSD 12 (released December 11th 2018): 3.15.5 (presumably upgraded
>> in a point release)
>> * NetBSD 8.1 (released May 31st 2019): 3.16.1
>> * NetBSD 9.0 (released February 14th 2020): 3.16.1
>> * OpenBSD: couldn’t find the version
>> * macOS: latest version is readily available through Homebrew
>> * Windows: You can install it yourself or use the one bundled with
Visual
>> Studio. I don't know what versions are bundled with Visual Studio;
some
>> searching suggests Visual Studio 2017 has CMake 3.12 and Visual Studio
2019
>> has 3.15, though I have no confirmation of that.
>>
>> Note that CMake provides prebuilt binaries for Linux, macOS, and
Windows,
>> and it’s also straightforward to build from source (it has very
>> conservative compiler requirements). One suggestion that was brought up
in
>> the past was for LLVM’s build system to just download a newer version
of
>> CMake if you attempted to build it using one that was too old, but
there
>> was opposition [1]. There was also a suggestion to have a script in
LLVM to
>> download and build CMake for you, but there were mixed opinions on this
too
>> [2], particularly since many developers might prefer downloading a
binary
>> release to building from source themselves (though of course the script
>> could also download binary releases if applicable). I personally think
>> downloading or building CMake yourself isn’t a high barrier for anyone
>> wanting to build LLVM (and in particular it’s *much* more
straightforward
>> than building LLVM itself), but I can understand why people would
prefer to
>> stick to versions available in distros.
>>
>> Another suggestion that came up last time was to set a policy for
>> upgrading CMake versions on some regular basis. The opposition to this
was
>> that we should upgrade CMake versions only when a newer version has a
>> compelling enough feature to justify upgrading, rather than always
>> upgrading. I can see arguments for both approaches, but we should
>> definitely at least think about the benefits we can get from upgrading
>> versions. I've gone through the CMake release notes and highlighted
>> features which seemed potentially valuable for LLVM. Note that I'm
only
>> highlighting features for which our minimum CMake version would have to
be
>> bumped up in order for our build system to take advantage of. There are
>> other useful features in newer CMake versions, but you can take
advantage
>> of them just by using a newer CMake yourself. For example, 3.9 loosens
the
>> dependencies of object compilation, which should result in faster Ninja
>> builds.
>>
>> CMake 3.5 (released March 8th 2016):
>> * install(DIRECTORY) supports generator expressions
>>
>> CMake 3.6 (released July 7th 2016):
>> * install() supports EXCLUDE_FROM_ALL
>> * list() supports FILTER to filter by regular expression
>> * Subninja support, which could theoretically be used for much faster
>> runtimes builds, although in practice we probably want to make
>> ExternalProject support this directly instead of trying to layer our
own
>> meta-build system on top
>> * CMAKE_TRY_COMPILE_TARGET_TYPE to tell try_compile to build a static
>> library instead of an executable, which will greatly simplify the
>> compiler-rt build
>>
>> CMake 3.7 (released November 11th 2016):
>> * New if() comparison operators LESS_EQUAL, GREATER_EQUAL,
STRLESS_EQUAL,
>> STRGREATER_EQUAL, VERSION_LESS_EQUAL, and VERSION_GREATER_EQUAL
>>
>> CMake 3.8 (released April 10th 2017):
>> * Compile features for C++17, which is required to build libc++
correctly
>> * Support for compile features for specific C++ features instead of
only
>> being able to specify standard versions
>> * rpath support via BUILD_RPATH target property and CMAKE_BUILD_RPATH
>> variable
>> * Apple framework support for static libraries
>> * New swig_add_library command in the UseSWIG module
>> * New generator expression $<IF:cond,true-value,false-value>
>>
>> CMake 3.9 (released July 18th 2017):
>> * install(TARGETS) and install(EXPORTS) support for object libraries,
>> which will simplify the compiler-rt build
>> * TARGET_OBJECTS generator expression support in add_custom_command and
>> file(GENERATE)
>> * $<TARGET_BUNDLE_DIR:tgt> and
$<TARGET_BUNDLE_CONTENT_DIR:tgt> generator
>> expressions for Apple bundles
>>
>> CMake 3.10 (released November 20th 2017):
>> * include_guard() command for proper guarding against double includes
of
>> CMake scripts
>> * An interesting aside is that this is the first verion of CMake to
>> require C++11 to build, which should give a good sense of how
conservative
>> they are about compiler requirements
>>
>> CMake 3.11 (released March 28th 2018):
>> * add_library() and add_executable() can be called without sources as
>> long as target_sources() is used later
>> * target_compile_{definitions,features,options},
>> target_include_directories(), target_sources(), and
target_link_libraries()
>> can set the corresponding INTERFACE_* properties on imported targets
>> * COMPILE_DEFINITIONS supports generator expressions
>> * COMPILE_OPTIONS source file property added
>> * INCLUDE_DIRECTORIES source file property added
>> * Interface libraries support custom properites
>>
>> CMake 3.12 (released July 17th 2018):
>> * add_compile_definitions() added to add compile definitions for
targets
>> (to avoid the global pollution caused by add_definitions())
>> * cmake_minimum_required() supports a version range to indicate tested
>> CMake versions and set policies accordingly
>> * file(TOUCH) and file(TOUCH_NOCREATE) added
>> * list(JOIN), list(SUBLIST) and list(TRANSFORM) added
>> * string(JOIN) added
>> * SHELL: prefix support in target_compile_options to avoid errant
>> deduplication
>> * target_link_libraries() supports object libraries and propagates
usage
>> requirements
>> * EXPORT_PROPERTIES target property to control the target properties
>> exported by export() and install(EXPORT)
>> * FindLibXml2 provides imported targets
>> * New FindPython, FindPython2, and FindPython3 modules to ease location
>> Python and selecting a specific version
>> * Modernization of UseSWIG module
>> * New generator expressions $<GENEX_EVAL:...>,
>> $<TARGET_GENEX_EVAL:target,...>, $<IN_LIST:...>,
$<TARGET_EXISTS:...> and
>> $<TARGET_NAME_IF_EXISTS:...>
>> * Compile features support for C++20
>>
>> CMake 3.13 (released November 20th 2018):
>> * cmake -E create_symlink supported on Windows
>> * target_link_directories() and target_link_options() commands to set
>> link options instead of awkwardly having to use target_link_libraries()
for
>> this purpose
>> * UseSWIG can manage INCLUDE_DIRECTORIES for SWIG compilation
>>
>> CMake 3.14 (released March 14th 2019):
>> * file(CREATE_LINK) to create hard or symbolic links
>> * if(DEFINED CACHE{VAR}) for checking if a cache variable is defined
>> * $<IN_LIST:...> generator expression correctly handles empty
argument
>> * Fixes for object library linking propagation
>> * Link options to manage position independent executables added
>> automatically
>>
>> CMake 3.15 (released July 17th 2019):
>> * list(PREPEND), list(POP_FRONT) and list(POP_BACK) added
>> * New message() types NOTICE, VERBOSE, DEBUG and TRACE
>> * string(REPEAT) added
>> * MSVC_RUNTIME_LIBRARY target property and CMAKE_MSVC_RUNTIME_LIBRARY
>> variable to select the runtime library type for MSVC
>> * $<C_COMPILER_ID:...>, $<CXX_COMPILER_ID:...>,
$<COMPILE_LANGUAGE:...>,
>> and $<PLATFORM_ID:...> generator expressions support matching one
value
>> from a list
>> * $<COMPILE_LANG_AND_ID:...> generator expression added
>> * $<FILTER:list,INCLUDE|EXCLUDE,regex> generator expression added
>> * $<REMOVE_DUPLICATES:list> generator expression added
>> * New $<TARGET_FILE*> generator expressions added:
>> $<TARGET_FILE_PREFIX:...>, $<TARGET_FILE_BASE_NAME:...>,
>> $<TARGET_FILE_SUFFIX:...>,
$<TARGET_LINKER_FILE_PREFIX:...>,
>> $<TARGET_LINKER_FILE_BASE_NAME:...>,
$<TARGET_LINKER_FILE_SUFFIX:...>,
>> $<TARGET_PDB_FILE_BASE_NAME:...>
>> * $<TARGET_OBJECTS:...> generator expression supports executables
and
>> static, shared, and module libraries
>>
>> CMake 3.16 (released November 26th 2019):
>> * Support for generator expressions in BUILD_RPATH and INSTALL_RPATH
>>
>> CMake 3.17 (released March 20th 2020):
>> * Ninja Multi-Config generator, which among other things would greatly
>> simplify LLVM_OPTIMIZED_TABLEGEN
>> * foreach(ZIP_LISTS) added to iterate multiple lists simultaneously
>> * New message() keywords CHECK_START, CHECK_PASS, and CHECK_FAIL
>> * INSTALL_NAME_DIR supports generator expressions
>>
>> Our build system is incredibly complex, and many of these features can
be
>> used to clean it up and make it much more maintainable. I would
personally
>> like us to at least bump up to CMake 3.12. I also do think it's
worth
>> establishing a policy and process around upgrading CMake versions,
since
>> newer versions keep on adding useful features (particularly better
>> generator expression support), and we want to be able to keep taking
>> advantage of them.
>>
>> [1] http://lists.llvm.org/pipermail/llvm-dev/2019-November/136485.html
>>
<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136485.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=HtGj57-MndDqyK71vXRwheQXms3WKx9rT-8WAVyTB3c&e=>
>> [2] http://lists.llvm.org/pipermail/llvm-dev/2019-November/136488.html
>>
<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136488.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=hHrZYrGk0WStJ3TjjIsXg2NMvVUP-f4woTFtaFlYkG8&e=>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
> _______________________________________________
> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> _______________________________________________
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Neil Nelson via llvm-dev

2020-Apr-04 22:31 UTC

head link

[llvm-dev] Upgrading LLVM's minimum required CMake version

I have seen here on the list that some are compiling on distribution 
versions older than 18.04. In using, for example, the Ubuntu 
distribution it is assumed that those interested in reliability and the 
more recent and better features will upgrade to the latest LTS version 
at the earliest convenience. For Xenial/16.04, the upgrade to 18.04 
should have been long ago.

I see you are taking precautions to restrict the cmake install for only 
clang and llvm and it looks reasonable. If this method is what is 
intended for clang and llvm, it would almost seem useful to make it part 
of the automated download procedure. It would become the standard with 
the rationale given as against other less restricted suggestions. Just 
saying get some particular cmake version does not obtain the suggested 
restricted requirement.

I am also using VMs (kvm) that increase the ease of using recent 
distribution releases and isolates whatever clang and llvm decides to do.

https://help.ubuntu.com/community/KVM/Installation

VMs have a number of advantages. A new ISO can be downloaded, a VM from 
the ISO running quickly, and then all the additional, interesting 
distribution software quickly installed on the VM without disturbing 
anything else. If for some reason that VM begins to have trouble, just 
delete it and try again. Keeping additional VMs in different stages of 
readiness helps the process along. Run the host on an LTS version if 
stability is desired or for other purposes, and the VMs having later 
versions with the wild software isolated.

Looks like a beta-release of Xubuntu 20.04 is here.

https://xubuntu.org/news/xubuntu-20-04-testing-week/

I will see if it will fly.

Neil Nelson

On 4/4/20 3:11 PM, Mehdi AMINI wrote:>
>
> On Sat, Apr 4, 2020 at 12:48 PM Neil Nelson via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>
>     'Supported' means that it comes from the packages available
from
>     the distribution that can be seen via this page.
>
>     https://packages.ubuntu.com/
>
>     These packages have been processed by the Ubuntu community to
>     obtain a reliability expectation that would not apply, for
>     example, to a PPA.
>
>
> Right, so I'm looking for an answer to my question, I'll try make
it
> more concrete what I mean by "in cases where we already requires a 
> more recent compiler than the default one available".
> If I take Xenial for instance, the most recent GCC version is 5.4.0 as 
> far as I can tell: https://packages.ubuntu.com/xenial/devel/gcc-5 ; 
> assuming LLVM would move at some point to require a more recent 
> version than 5.4, it would mean that you couldn't build LLVM with the 
> packages available on Xenial. In this situation (which I referred to 
> as "cases where we already requires a more recent compiler than the 
> default one available") we already expect the user to get a toolchain 
> from a non-primary package source on this distribution, and if we do 
> this for the toolchain already I would expect that we should be able 
> to do it as well for CMake (again: for a given distribution/version).
>
>     The difference between installing or building Clang and LLVM from
>     original sources as against installing versions available from the
>     distribution
>
> I don't understand this sentence?
>
>     when compared to doing the same with cmake, is that the user
>     accepts the inherent risks from Clang and LLVM, but Clang and LLVM
>     can not accept the risks from the cmake group and then expect the
>     user to merely assume that there are no additional risks from
>     installing cmake.
>
> Maybe a nit here, but there is no need to *install* CMake: it could be 
> trivially build in the build directory. We are talking about a trivial 
> step here:
>
> # Inside llvm-project/
> $ mkdir build/ && cd build/
> # bootstrap CMake
> $ wget 
>
https://github.com/Kitware/CMake/releases/download/v3.17.0/cmake-3.17.0.tar.gz
> $ echo 
> "b74c05b55115eacc4fa2b77a814981dbda05cdc95a53e279fe16b7b272f00847 
>  cmake-3.17.0.tar.gz" | sha256sum -c
> $ tar -xf cmake-3.17.0.tar.gz && cd cmake-3.17.0 &&
./bootstrap && make
> # Done, cmake is usable, *nothing* is installed on the user system, 
> everything is self-contained *inside* the build directory itself.
> $ ./cmake-3.17.0/bin/cmake ../llvm/ -D.... # build LLVM as usual.
>
>
>
>     The distributions are not merely just collections of software,
>     they are collections of software that have some guarantee of
>     working well together and without bugs and other issues because
>     they have been used and tested by that use in the distribution
>     community.
>
>     The importance of this distinction between the quality of software
>     expected in a distribution as against installing directly from
>     source is apparently lost on those who did not live through the
>     pre-distribution days. During that time we had to gather up the
>     dependencies ourselves, trying to get the correct versions, hoping
>     that the software compiled and worked with the other dependencies,
>     and hope we did not install malware and hackware. And quite often
>     it was a futile attempt to gather together software dependencies
>     of any size.
>
>     Those who lived through that time remember it as the dark-ages of
>     long ago, never to be seen again.
>
> Been there, done that... (actually suffered from that).
>
> I claim this is just not the same situation here: CMake is a 
> self-contained dependencies and as shown above does not need to escape 
> anywhere outside the build directory.
>
> -- 
> Mehdi
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Chris Tetreault via llvm-dev

2020-Apr-06 19:48 UTC

head link

[llvm-dev] Upgrading LLVM's minimum required CMake version

Every additional dependency that we force the user to manually install (either
by building from source, or adding some new PPA to their ubuntu system), raises
the barrier to entry that much higher. Just because we may require the user to
manually install some newer compiler on their system doesn’t mean that we should
also require them to install some newer CMake than what’s on their system.
(unless it is actually necessary, but we’ve beaten that dead horse long enough)

I agree with Neil’s interpretation that the definition of “supported” being used
here is default system packages and not third party repos that claim to work for
that system.

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Mehdi
AMINI via llvm-dev
Sent: Saturday, April 4, 2020 2:11 PM
To: Neil Nelson <nnelson at infowest.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: [EXT] Re: [llvm-dev] Upgrading LLVM's minimum required CMake
version



On Sat, Apr 4, 2020 at 12:48 PM Neil Nelson via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

'Supported' means that it comes from the packages available from the
distribution that can be seen via this page.

https://packages.ubuntu.com/

These packages have been processed by the Ubuntu community to obtain a
reliability expectation that would not apply, for example, to a PPA.

Right, so I'm looking for an answer to my question, I'll try make it
more concrete what I mean by "in cases where we already requires a more
recent compiler than the default one available".
If I take Xenial for instance, the most recent GCC version is 5.4.0 as far as I
can tell: https://packages.ubuntu.com/xenial/devel/gcc-5 ; assuming LLVM would
move at some point to require a more recent version than 5.4, it would mean that
you couldn't build LLVM with the packages available on Xenial. In this
situation (which I referred to as "cases where we already requires a more
recent compiler than the default one available") we already expect the user
to get a toolchain from a non-primary package source on this distribution, and
if we do this for the toolchain already I would expect that we should be able to
do it as well for CMake (again: for a given distribution/version).


The difference between installing or building Clang and LLVM from original
sources as against installing versions available from the distribution
I don't understand this sentence?


when compared to doing the same with cmake, is that the user accepts the
inherent risks from Clang and LLVM, but Clang and LLVM can not accept the risks
from the cmake group and then expect the user to merely assume that there are no
additional risks from installing cmake.
Maybe a nit here, but there is no need to *install* CMake: it could be trivially
build in the build directory. We are talking about a trivial step here:

# Inside llvm-project/
$ mkdir build/ && cd build/
# bootstrap CMake
$ wget
https://github.com/Kitware/CMake/releases/download/v3.17.0/cmake-3.17.0.tar.gz
$ echo "b74c05b55115eacc4fa2b77a814981dbda05cdc95a53e279fe16b7b272f00847 
cmake-3.17.0.tar.gz" | sha256sum -c
$ tar -xf cmake-3.17.0.tar.gz && cd cmake-3.17.0 && ./bootstrap
&& make
# Done, cmake is usable, *nothing* is installed on the user system, everything
is self-contained *inside* the build directory itself.
$ ./cmake-3.17.0/bin/cmake ../llvm/ -D.... # build LLVM as usual.




The distributions are not merely just collections of software, they are
collections of software that have some guarantee of working well together and
without bugs and other issues because they have been used and tested by that use
in the distribution community.

The importance of this distinction between the quality of software expected in a
distribution as against installing directly from source is apparently lost on
those who did not live through the pre-distribution days. During that time we
had to gather up the dependencies ourselves, trying to get the correct versions,
hoping that the software compiled and worked with the other dependencies, and
hope we did not install malware and hackware. And quite often it was a futile
attempt to gather together software dependencies of any size.

Those who lived through that time remember it as the dark-ages of long ago,
never to be seen again.
Been there, done that... (actually suffered from that).

I claim this is just not the same situation here: CMake is a self-contained
dependencies and as shown above does not need to escape anywhere outside the
build directory.

--
Mehdi


On 4/4/20 11:48 AM, Mehdi AMINI via llvm-dev wrote:


On Thu, Apr 2, 2020 at 10:49 AM Shoaib Meenai via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I’m in favor of all this. Thanks for volunteering! I’m happy to help out in
whatever way.

Some things it might be worth figuring out for future upgrades:
* If we want to limit ourselves to CMake versions supported by LTS releases of
distros, which distros should we consider, and how far back should we go (i.e.
is it just the latest LTS or the last two LTS versions)?

Can you clarify what "supported" means? Does it include PPA on ubuntu
for example?
I wouldn't limit ourselves artificially to the version of CMake
"natively" available on an OS in cases where we already requires a
more recent compiler than the default one available: if we consider OK to
require as user to build clang or gcc from source or use a PPA, we should be OK
the same way with CMake.


* For platforms like Ubuntu where CMake publishes its own packages (that you can
install via the platform’s package manager), do those count, or do we only
consider the CMake that comes in the OS packages?
* Do we have any limitations around how often/when we upgrade? You’re tying the
upgrade to after the branch, which is pretty standard, but e.g. if we wanted to
upgrade to 3.8.0 now and then upgrade to 3.13.4 after the branch, would people
be okay with that, or should we limit upgrades to just shortly after a branch?

From: <ldionne at apple.com<mailto:ldionne at apple.com>> on behalf
of Louis Dionne <ldionne at apple.com<mailto:ldionne at apple.com>>
Date: Thursday, April 2, 2020 at 7:20 AM
To: Shoaib Meenai <smeenai at fb.com<mailto:smeenai at fb.com>>
Cc: "llvm-dev at lists.llvm.org<mailto:llvm-dev at
lists.llvm.org>" <llvm-dev at lists.llvm.org<mailto:llvm-dev at
lists.llvm.org>>, Chris Bieneman <beanz at apple.com<mailto:beanz at
apple.com>>, Petr Hosek <phosek at chromium.org<mailto:phosek at
chromium.org>>, Saleem Abdulrasool <compnerd at
compnerd.org<mailto:compnerd at compnerd.org>>, "tstellar at
redhat.com<mailto:tstellar at redhat.com>" <tstellar at
redhat.com<mailto:tstellar at redhat.com>>
Subject: Re: Upgrading LLVM's minimum required CMake version

Okay, so we've had some discussion on this thread, and although some people
(including me) would like a more aggressive policy, I believe the following will
not get any objection (based on the thread). On April 23rd 2020, Ubuntu 20.04
LTS will ship with CMake 3.16.x. This will make the lower bound for LTS
distributions be 3.13.4, and so I suggest we upgrade to that. Here's a
proposed process:

1. Immediately add a CMake warning in <root>/llvm/CMakeLists.txt saying
that CMake 3.13.4 will be the new minimum version starting with LLVM 12.0.0, and
mentioning the versions used in various LTSes.
2. Immediately send a courtesy heads-up email to all build-bot owners telling
them about the upcoming change.
3. Right after we branch off the release branch for LLVM 11.0.0 (the next one),
make the minimum CMake version required be 3.13.4.
4. Iterate on (3) until all bots are migrated.
5. Send a message to the list saying the bump is complete. At that time,
projects are free to start using features from 3.13.4.

Unless someone else absolutely wants to bite the bullet, I volunteer to do the
above steps.

Thoughts?

Louis


On Mar 26, 2020, at 16:07, Shoaib Meenai <smeenai at fb.com<mailto:smeenai
at fb.com>> wrote:

We had this discussion a few months ago and it petered out, and it’s recently
been revived in the context of upgrading the CMake version specifically for
libc++ (at which point people suggested upgrading the CMake version used by all
of LLVM), so let’s try to move this forward.

Our current required minimum version is CMake 3.4.3, which was released on
January 25th 2016. It’s interesting to note that LLVM started requiring 3.4.3 on
May 31st 2016, which was just 4 months after its release.

Let’s look at the CMake versions available on various distros and operating
systems. I’m unfamiliar with many of these, so I apologize if I get something
wrong. (I’m using
pkgs.org<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
for most of this information.)
* RHEL 6 (released Nov 10th 2010) : 3.6.1 (via EPEL)
* RHEL 7 (released June 10th 2014): 3.14.7 (via EPEL)
* RHEL 8 (released May 7th 2019): 3.11.4 (maybe
pkgs.org<https://urldefense.proofpoint.com/v2/url?u=http-3A__pkgs.org&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=S6Qvuq5DqECZFfItkAJOL5xjTSp1psRWYtq_WOnXt_o&e=>
is screwy on this one, because it doesn’t make sense that RHEL 7 should have a
newer available version than RHEL 8)
* Debian 9 (released June 17th 2017): 3.7.2
* Debian 10 (released July 6th 2019): 3.13.4
* Ubuntu 16.04 LTS (released April 21st 2016): 3.5.1
* Ubuntu 18.04 LTS (released April 26th 2018): 3.10.2
* FreeBSD 11 (released October 10th 2016): 3.15.5 (presumably upgraded in a
point release)
* FreeBSD 12 (released December 11th 2018): 3.15.5 (presumably upgraded in a
point release)
* NetBSD 8.1 (released May 31st 2019): 3.16.1
* NetBSD 9.0 (released February 14th 2020): 3.16.1
* OpenBSD: couldn’t find the version
* macOS: latest version is readily available through Homebrew
* Windows: You can install it yourself or use the one bundled with Visual
Studio. I don't know what versions are bundled with Visual Studio; some
searching suggests Visual Studio 2017 has CMake 3.12 and Visual Studio 2019 has
3.15, though I have no confirmation of that.

Note that CMake provides prebuilt binaries for Linux, macOS, and Windows, and
it’s also straightforward to build from source (it has very conservative
compiler requirements). One suggestion that was brought up in the past was for
LLVM’s build system to just download a newer version of CMake if you attempted
to build it using one that was too old, but there was opposition [1]. There was
also a suggestion to have a script in LLVM to download and build CMake for you,
but there were mixed opinions on this too [2], particularly since many
developers might prefer downloading a binary release to building from source
themselves (though of course the script could also download binary releases if
applicable). I personally think downloading or building CMake yourself isn’t a
high barrier for anyone wanting to build LLVM (and in particular it’s *much*
more straightforward than building LLVM itself), but I can understand why people
would prefer to stick to versions available in distros.

Another suggestion that came up last time was to set a policy for upgrading
CMake versions on some regular basis. The opposition to this was that we should
upgrade CMake versions only when a newer version has a compelling enough feature
to justify upgrading, rather than always upgrading. I can see arguments for both
approaches, but we should definitely at least think about the benefits we can
get from upgrading versions. I've gone through the CMake release notes and
highlighted features which seemed potentially valuable for LLVM. Note that
I'm only highlighting features for which our minimum CMake version would
have to be bumped up in order for our build system to take advantage of. There
are other useful features in newer CMake versions, but you can take advantage of
them just by using a newer CMake yourself. For example, 3.9 loosens the
dependencies of object compilation, which should result in faster Ninja builds.

CMake 3.5 (released March 8th 2016):
* install(DIRECTORY) supports generator expressions

CMake 3.6 (released July 7th 2016):
* install() supports EXCLUDE_FROM_ALL
* list() supports FILTER to filter by regular expression
* Subninja support, which could theoretically be used for much faster runtimes
builds, although in practice we probably want to make ExternalProject support
this directly instead of trying to layer our own meta-build system on top
* CMAKE_TRY_COMPILE_TARGET_TYPE to tell try_compile to build a static library
instead of an executable, which will greatly simplify the compiler-rt build

CMake 3.7 (released November 11th 2016):
* New if() comparison operators LESS_EQUAL, GREATER_EQUAL, STRLESS_EQUAL,
STRGREATER_EQUAL, VERSION_LESS_EQUAL, and VERSION_GREATER_EQUAL

CMake 3.8 (released April 10th 2017):
* Compile features for C++17, which is required to build libc++ correctly
* Support for compile features for specific C++ features instead of only being
able to specify standard versions
* rpath support via BUILD_RPATH target property and CMAKE_BUILD_RPATH variable
* Apple framework support for static libraries
* New swig_add_library command in the UseSWIG module
* New generator expression $<IF:cond,true-value,false-value>

CMake 3.9 (released July 18th 2017):
* install(TARGETS) and install(EXPORTS) support for object libraries, which will
simplify the compiler-rt build
* TARGET_OBJECTS generator expression support in add_custom_command and
file(GENERATE)
* $<TARGET_BUNDLE_DIR:tgt> and $<TARGET_BUNDLE_CONTENT_DIR:tgt>
generator expressions for Apple bundles

CMake 3.10 (released November 20th 2017):
* include_guard() command for proper guarding against double includes of CMake
scripts
* An interesting aside is that this is the first verion of CMake to require
C++11 to build, which should give a good sense of how conservative they are
about compiler requirements

CMake 3.11 (released March 28th 2018):
* add_library() and add_executable() can be called without sources as long as
target_sources() is used later
* target_compile_{definitions,features,options}, target_include_directories(),
target_sources(), and target_link_libraries() can set the corresponding
INTERFACE_* properties on imported targets
* COMPILE_DEFINITIONS supports generator expressions
* COMPILE_OPTIONS source file property added
* INCLUDE_DIRECTORIES source file property added
* Interface libraries support custom properites

CMake 3.12 (released July 17th 2018):
* add_compile_definitions() added to add compile definitions for targets (to
avoid the global pollution caused by add_definitions())
* cmake_minimum_required() supports a version range to indicate tested CMake
versions and set policies accordingly
* file(TOUCH) and file(TOUCH_NOCREATE) added
* list(JOIN), list(SUBLIST) and list(TRANSFORM) added
* string(JOIN) added
* SHELL: prefix support in target_compile_options to avoid errant deduplication
* target_link_libraries() supports object libraries and propagates usage
requirements
* EXPORT_PROPERTIES target property to control the target properties exported by
export() and install(EXPORT)
* FindLibXml2 provides imported targets
* New FindPython, FindPython2, and FindPython3 modules to ease location Python
and selecting a specific version
* Modernization of UseSWIG module
* New generator expressions $<GENEX_EVAL:...>,
$<TARGET_GENEX_EVAL:target,...>, $<IN_LIST:...>,
$<TARGET_EXISTS:...> and $<TARGET_NAME_IF_EXISTS:...>
* Compile features support for C++20

CMake 3.13 (released November 20th 2018):
* cmake -E create_symlink supported on Windows
* target_link_directories() and target_link_options() commands to set link
options instead of awkwardly having to use target_link_libraries() for this
purpose
* UseSWIG can manage INCLUDE_DIRECTORIES for SWIG compilation

CMake 3.14 (released March 14th 2019):
* file(CREATE_LINK) to create hard or symbolic links
* if(DEFINED CACHE{VAR}) for checking if a cache variable is defined
* $<IN_LIST:...> generator expression correctly handles empty argument
* Fixes for object library linking propagation
* Link options to manage position independent executables added automatically

CMake 3.15 (released July 17th 2019):
* list(PREPEND), list(POP_FRONT) and list(POP_BACK) added
* New message() types NOTICE, VERBOSE, DEBUG and TRACE
* string(REPEAT) added
* MSVC_RUNTIME_LIBRARY target property and CMAKE_MSVC_RUNTIME_LIBRARY variable
to select the runtime library type for MSVC
* $<C_COMPILER_ID:...>, $<CXX_COMPILER_ID:...>,
$<COMPILE_LANGUAGE:...>, and $<PLATFORM_ID:...> generator
expressions support matching one value from a list
* $<COMPILE_LANG_AND_ID:...> generator expression added
* $<FILTER:list,INCLUDE|EXCLUDE,regex> generator expression added
* $<REMOVE_DUPLICATES:list> generator expression added
* New $<TARGET_FILE*> generator expressions added:
$<TARGET_FILE_PREFIX:...>, $<TARGET_FILE_BASE_NAME:...>,
$<TARGET_FILE_SUFFIX:...>, $<TARGET_LINKER_FILE_PREFIX:...>,
$<TARGET_LINKER_FILE_BASE_NAME:...>,
$<TARGET_LINKER_FILE_SUFFIX:...>, $<TARGET_PDB_FILE_BASE_NAME:...>
* $<TARGET_OBJECTS:...> generator expression supports executables and
static, shared, and module libraries

CMake 3.16 (released November 26th 2019):
* Support for generator expressions in BUILD_RPATH and INSTALL_RPATH

CMake 3.17 (released March 20th 2020):
* Ninja Multi-Config generator, which among other things would greatly simplify
LLVM_OPTIMIZED_TABLEGEN
* foreach(ZIP_LISTS) added to iterate multiple lists simultaneously
* New message() keywords CHECK_START, CHECK_PASS, and CHECK_FAIL
* INSTALL_NAME_DIR supports generator expressions

Our build system is incredibly complex, and many of these features can be used
to clean it up and make it much more maintainable. I would personally like us to
at least bump up to CMake 3.12. I also do think it's worth establishing a
policy and process around upgrading CMake versions, since newer versions keep on
adding useful features (particularly better generator expression support), and
we want to be able to keep taking advantage of them.

[1]
http://lists.llvm.org/pipermail/llvm-dev/2019-November/136485.html<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136485.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=HtGj57-MndDqyK71vXRwheQXms3WKx9rT-8WAVyTB3c&e=>
[2]
http://lists.llvm.org/pipermail/llvm-dev/2019-November/136488.html<https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2019-2DNovember_136488.html&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=atRWn0u_rLa9ITqRSW-W8QvRJN244hhQmDWillcW3gE&s=hHrZYrGk0WStJ3TjjIsXg2NMvVUP-f4woTFtaFlYkG8&e=>

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