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

Sat Apr 4 10:48:04 PDT 2020

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=>
>
>
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