[llvm-dev] [RFC] LLVM Directory Structure Changes (was Re: [PATCH] D20992: [CMake] Add LLVM runtimes directory)

Chris Bieneman via llvm-dev
Fri, 10 Jun 2016 17:52:22 -0000

It seems to me that the feedback here has been generally positive, but a lot of
different ideas have been added to the mix.

To focus conversation and move things along I'm going to provide a summary
of changes with proposals for rollout.

Splitting Compiler-RT

If we want to split compiler-rt, which I think makes a lot of sense, I think the
best path forward is to copy the trunk (via svn cp). Copying the branch is the
best way to preserve the history and workflows.

For naming purposes I would suggest retaining the compiler-rt name for the
builtin libraries, and having a repository named sanitizer-rt for the sanitizer
libraries (this is of course just a suggestion, feel free to bike shed).

After duplicating the repository we could setup an auto-merge from compiler-rt
to sanitizer-rt. We could setup the LLVM build system so that if both projects
were present it would force only building builtins from compiler-rt and
sanitizers from sanitizer-rt. This would allow a transition time where bots
could be updated to include both repositories, and engineer workflows would not
be impacted.

After a brief time for bots to be updated with the new repository we could
modify the repositories separately to build only the parts they are supposed to
build, remove the hack from LLVM to force that, and begin removing code from the
separate repositories.

LLVM Restructuring

The first step here is adding the new functionality, iterating on the CMake
interface for the runtime projects and getting all the runtime projects hooked
up.

Once all the runtime project support is ready we can begin migrating bots and
evangelizing the new runtime build process.

At some point before or after the runtime work we can modify CMake to support
the test-suite living under tests (or somewhere else, bikeshed away).

Once runtime support is ready, and the test-suite is supported outside projects
we can set a date for removal of the projects directory. This planning should
take into account updating bots as well as updating scripts and tooling.

Breaking out testing tools

As I started looking into breaking out the testing tools I realized it is *much*
more complicated than I had first thought. I do think that it is a good idea to
do this, but it is going to be a bigger change than I had originally thought.

The big wrench in breaking out the testing tools is that you need more than just
lit. In particular you need FileCheck, not, count and a few other random things
under llvm/utils. This also means you need to break out libSupport and ADT.

While I think that breaking this stuff all out is a good idea, it is a much
larger change than what I was trying to propose. If we go down this route I
would recommend creating a new llvm-infrastructure repository. We could then
stub it out and update projects and workflows to include it. After the workflows
are updated we can start moving libraries and tools into it.

An alternative approach we could take would be to migrate the testing tools off
libSupport to make them standalone. Then the testing tools and lit could more
easily be lifted out of the LLVM repository. This approach has some benefits,
but also has added complication because some of the libSupport functionality in
use is non-trivial.

Thoughts?
-Chris


> On Jun 9, 2016, at 2:09 PM, Craig, Ben <ben.craig at codeaurora.org>
wrote:
>
>
>>> To get cmake to work, I have to set HAVE_CXX_ATOMICS_WITHOUT_LIB,
even though I have no intention of building LLVM.  I then get to set
LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB too, because reasons.
>> This is bad. I’m curious why you need to set those ever. Have you
diagnosed this? For you to need to set that it means the host toolchain isn’t
properly passing the CMake checks.
> It looks like I don't need to set these anymore, but the comment that I
left myself at the time was that HAVE_CXX_ATOMICS_WITHOUT_LIB looked at the
state of my local machine's toolchain, as opposed to the toolchain that I
was about to use.  My local machine's toolchain is gcc 4.6.3, and it
doesn't have an <atomic> header.
>
>>> Multi-libs require multiple independent build directories, with all
the associated cmake overhead.
>> I strongly believe that for building multi-lib or more generally when
building for multiple targets you want multiple           build directories, and
in particular the multiple-cmake invocations. I believe this because you want
the checks to be relevant for the target, and the only way to do that is to run
the checks once per target.
>>
>> That said, I also strongly believe that for any user of our projects we
should find a way to have a single simple CMake invocation that gets the end
result that you want. I don’t believe these are mutually exclusive goals.
>>
>> One of the development steps of the new runtime directory will be
supporting specifying multiple targets to build the runtimes for, and having
CMake construct the appropriate number of build directories and manage building
them all through a single top-level configuration and build directory. If you’re
skeptical about how doable this is I’d encourage you to look at this bot ->
http://lab.llvm.org:8011/builders/clang-3stage-ubuntu
<http://lab.llvm.org:8011/builders/clang-3stage-ubuntu>.
>>
>> That bot does a full 3-stage clang build from a single CMake
invocation:
>>
>> cmake -C ../llvm.src/tools/clang/cmake/caches/3-stage.cmake -GNinja
-DLLVM_TARGETS_TO_BUILD=all -DLLVM_BINUTILS_INCDIR=/opt/binutils/include
../llvm.src
>>
> I'm fine if I can invoke cmake once and get multiple library variants
out.  If that means that behind-the-scenes, cmake has multiple build
sub-directories, then that's fine by me.  On Windows, this already happens
to some degree, as the Visual Studio project is allowed to switch between
Release, Debug, RelWithDebInfo, etc without re-running cmake.
>
>>> So why not run out of tree instead you may ask?
>>>
>>> No lit tests or lit utilities (FileCheck, not, etc…)
>> I don’t know if the runtimes you’re building are setup for this or not,
but you can get out-of-tree tests working if you have an LLVM installation on
the system or a build directory that you can point at. Compiler-RT does this. It
isn’t ideal but it is workable.
>>
>> We should have a better solution.
> The nightly builds that my organization produces is generally a
"customer build", and not a "developer build".  Stated
otherwise, it doesn't include llvm-config, libclang.a, or any of the other
things that people building against llvm would want.  That means that if I
wanted to use this particular out-of-tree solution, I would still need to clone
down LLVM and rebuild and reinstall it on occasion.
>
>>> So some things I would like to see...
>>>
>>> Standalone runtime builds should use the "normal" build
interfaces (bare make, make all, make check, make install.  s/make/ninja as
desired).
>> I think this is doable, but I’m hesitant to rope it in with what I’m
trying to do here. Nothing I want to do would prevent this or make it any harder
than it already is.
> Completely fair.  I figured I'd get my grievances and wishlist out
first, just so that some agreement on a direction can be figured out.  It does
extend beyond the directory re-org patch.
>
>>> Break out testing infrastructure to a common repo, so that the
runtimes can have access to the testing "banana" without dragging
along the LLVM "gorilla”.
>> I’m hesitant to suggest more and more repos because I think there are
some challenges and additional burdens with that. I do understand the benefit of
what you’re asking for here, and I think it is worth considering. I think there
is an argument for splitting out the LLVM testing infrastructure, as well as an
argument for splitting out the LLVM build infrastructure.
>>
>> In both cases I think those changes are larger than what I’m proposing,
but worth considering.
>>
>> -Chris
>>
>> Obligatory troll: Maybe we should move to github and change the whole
repo structure in the process?
> I figured the github thread was crazy enough without me sabotaging it with
this kind of suggestion :)
>
>>>
>>>
>>> On 6/9/2016 12:20 PM, Chris Bieneman via llvm-dev wrote:
>>>> Moving to llvm-dev (I think this has gone a bit further than a
patch review discussion)
>>>>
>>>> In hindsight I probably should have explained more of my
thinking on this with the patch, or done an RFC on llvm-dev to start with. I’l
do that now, and answer the questions along the way. I sent a separate email
discussing Justin’s patch review feedback.
>>>>
>>>> In the build system today there is no strong distinction
between ‘projects’ and ‘tools’. There are a few subtle differences, but I’m not
sure any of them really matter. The differences are:
>>>>
>>>> (1) The projects directory is always configured, tools can be
disabled using LLVM_INCLUDE_TOOLS=Off (projects and tools can both be
individually disabled too)
>>>> (2) Projects are configured before tools, so tools can rely on
targets being created for projects (we don’t really use this, and anywhere we
are is probably a bug)
>>>> (3) Some projects have special handling. For example test-suite
isn’t actually treated as a project, it has special handling in
LLVM/CMakeLists.txt:727, and Compiler-RT is handled by clang if you set
LLVM_BUILD_EXTERNAL_COMPILER_RT=On.
>>>>
>>>> With this in mind I was thinking about the general usability of
our build system. The distinction between a project and a tool is not very
clear. At a high level I see three different use cases that are covered by our
current projects & tools directories.
>>>>
>>>> (1) Projects that are configured with LLVM
>>>> (2) Runtime projects that should be configured using the
just-built tools
>>>> (3) The LLVM test-suite, which is really just external tests
that should be configured and run with the just-built tools
>>>>
>>>> My proposal is that we make the tools subdirectory the *only*
place for projects that fall into category 1. I don’t think there is any
technical reason to drop an in-tree project into projects over tools today, and
I think we migrating people who are doing that away from it should be easy.
>>>>
>>>> Second I want to add a “runtimes” directory to LLVM to cover
case 2 (see D20992). The idea behind this is to use common code in LLVM to
support building runtimes. This will allow the full LLVM toolchain to be visible
during configuration. I will abstract this functionality into an installed CMake
module so that Clang can use it for out-of-tree clang builds.
>>>>
>>>> Lastly we need to give the test-suite a new home. I’m not super
concerned with where we do that. It could be under tests, it could just be at
the root of the LLVM directory. I don’t think it matters too much because it is
a one-off. Thoughts welcome.
>>>>
>>>> My proposed patch makes the runtimes directory work for
Compiler-RT, but it doesn’t yet handle libcxxabi, libcxx and libunwind. There is
some special case handling between libcxxabi and libcxx that will need to be
handled to make the dependencies work between the two, and I still need to work
that out.
>>>>
>>>> If we want to go with this proposal I envision the transition
being multi-staged:
>>>>
>>>> (1) Adding the new functionality, getting it up and fully
working for all runtime projects - this will involve changes to runtime projects
>>>> (2) Work with bot maintainers to migrate bots, and fix any
issues that come up
>>>> (3) Add support for a new secondary location for the test-suite
>>>> (4) Set a date for removing the projects directory, post
patches including updated documentation
>>>> (5) Remove the projects directory entirely
>>>>
>>>> Thoughts?
>>>> -Chris
>>>>
>>>>> On Jun 8, 2016, at 6:59 PM, Chandler Carruth <chandlerc
at gmail.com <mailto:chandlerc at gmail.com>> wrote:
>>>>>
>>>>> On Wed, Jun 8, 2016 at 4:39 PM Justin Bogner via
llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at
lists.llvm.org>> wrote:
>>>>> Chris Bieneman <beanz at apple.com <mailto:beanz at
apple.com>> writes:
>>>>> > beanz created this revision.
>>>>> > beanz added reviewers: chandlerc, bogner.
>>>>> > beanz added a subscriber: llvm-commits.
>>>>> >
>>>>> > There are a few LLVM projects that produce runtime
libraries. Ideally
>>>>> > runtime libraries should be built differently than
other projects,
>>>>> > specifically they should be built using the just-built
toolchain.
>>>>> >
>>>>> > There is support for building compiler-rt in this way
from the clang
>>>>> > build. Moving this logic into the LLVM build is
interesting because it
>>>>> > provides a simpler way to extend the just-built
toolchain to include
>>>>> > LLD and the LLVM object file tools.
>>>>> >
>>>>> > Once this functionality is better fleshed out and
tested we’ll want to
>>>>> > encapsulate it in a module that can be used for clang
standalone
>>>>> > builds, and we’ll want to make it the default way to
build compiler-rt.
>>>>> >
>>>>> > With this patch applied there is no immediate change
in the build.
>>>>> > Moving compiler-rt out from llvm/projects into
llvm/runtimes enables
>>>>> > the functionality.
>>>>>
>>>>> This seems reasonable, but I am a little worried about how
transitioning
>>>>> to the new system will work. Will everyone have to move
their
>>>>> compiler-rt checkout? Will we continue to support
compiler-rt in either
>>>>> place? Both of these are workable, but neither is great.
Thoughts?
>>>>>
>>>>> I share your concerns, but I also kind of like the
direction this is going.
>>>>>
>>>>> But there is a higher-level meta-point: do we want to keep
the 'projects' directory *at all*.
>>>>>
>>>>> Every single resident of it I can think of except for the
test-suite is either dead (dragonegg) or a runtime library.
>>>>>
>>>>> I think we should either have all the build-integrated
projects in a single 'projects' directory (including LLD and Clang), or
we should have none of them and use more domain relevant organization (today
"tools", you're adding "runtimes", maybe we move the
test-suite to go under one of the test directories).
>>>>>
>>>>> I think we should have a consistent plan here before moving
stuff. But once we have it, I think we shouldn't be afraid of re-organizing
stuff to make more sense, and just work to get folks to update their checkouts.
>>>>>
>>>>> -Chandler
>>>>>
>>>>>
>>>>> > This code has a few improvements over the method
provided by
>>>>> > LLVM_BUILD_EXTERNAL_COMPILER_RT. Specifically the
sub-ninja command is
>>>>> > always invoked, so changes to compiler-rt source files
will get built
>>>>> > properly, so this patch can be used for iterative
development with
>>>>> > just-built tools.
>>>>> >
>>>>> >
<http://reviews.llvm.org/D20992>http://reviews.llvm.org/D20992
<http://reviews.llvm.org/D20992>
>>>>> >
>>>>> > Files:
>>>>> >   CMakeLists.txt
>>>>> >   cmake/modules/LLVMExternalProjectUtils.cmake
>>>>> >   runtimes/CMakeLists.txt
>>>>> >
>>>>> > Index: runtimes/CMakeLists.txt
>>>>> >
==================================================================>>>>>
> --- /dev/null
>>>>> > +++ runtimes/CMakeLists.txt
>>>>> > @@ -0,0 +1,16 @@
>>>>> > +include(LLVMExternalProjectUtils)
>>>>> > +
>>>>> > +# Discover the projects that use CMake in the
subdirectories.
>>>>> > +# Note that explicit cmake invocation is required
every time a new project is
>>>>> > +# added or removed.
>>>>> > +
>>>>> > +add_custom_target(runtimes)
>>>>> > +
>>>>> > +file(GLOB entries *)
>>>>> > +foreach(entry ${entries})
>>>>> > +  if(IS_DIRECTORY ${entry} AND EXISTS
${entry}/CMakeLists.txt)
>>>>> > +    get_filename_component(projName ${entry} NAME)
>>>>> > +    llvm_ExternalProject_Add(${projName} ${entry}
USE_TOOLCHAIN)
>>>>> > +    add_dependencies(runtimes ${projName})
>>>>> > +  endif()
>>>>> > +endforeach(entry)
>>>>> > Index: cmake/modules/LLVMExternalProjectUtils.cmake
>>>>> >
==================================================================>>>>>
> --- cmake/modules/LLVMExternalProjectUtils.cmake
>>>>> > +++ cmake/modules/LLVMExternalProjectUtils.cmake
>>>>> > @@ -29,7 +29,8 @@
>>>>> >  #     Extra targets in the subproject to generate
targets for
>>>>> >  #   )
>>>>> >  function(llvm_ExternalProject_Add name source_dir)
>>>>> > -  cmake_parse_arguments(ARG
"USE_TOOLCHAIN;EXCLUDE_FROM_ALL;NO_INSTALL"
>>>>> > +  cmake_parse_arguments(ARG
>>>>> > +
"USE_TOOLCHAIN;EXCLUDE_FROM_ALL;NO_INSTALL;ALWAYS_CLEAN"
>>>>> >      "SOURCE_DIR"
>>>>> >
"CMAKE_ARGS;TOOLCHAIN_TOOLS;RUNTIME_LIBRARIES;DEPENDS;EXTRA_TARGETS"
${ARGN})
>>>>> >    canonicalize_tool_name(${name} nameCanon)
>>>>> > @@ -52,6 +53,10 @@
>>>>> >      endif()
>>>>> >    endforeach()
>>>>> >
>>>>> > +  if(ARG_ALWAYS_CLEAN)
>>>>> > +    set(always_clean clean)
>>>>> > +  endif()
>>>>> > +
>>>>> >    list(FIND TOOLCHAIN_TOOLS clang FOUND_CLANG)
>>>>> >    if(FOUND_CLANG GREATER -1)
>>>>> >      set(CLANG_IN_TOOLCHAIN On)
>>>>> > @@ -135,6 +140,14 @@
>>>>> >      CMAKE_ARGS ${${nameCanon}_CMAKE_ARGS}
>>>>> >                 ${compiler_args}
>>>>> >
-DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
>>>>> > +
-DLLVM_CONFIG_PATH=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-config
>>>>> > +
-DLLVM_LIBRARY_OUTPUT_INTDIR=${LLVM_LIBRARY_OUTPUT_INTDIR}
>>>>> > +
-DLLVM_RUNTIME_OUTPUT_INTDIR=${LLVM_RUNTIME_OUTPUT_INTDIR}
>>>>> > +
-DLLVM_LIBDIR_SUFFIX=${LLVM_LIBDIR_SUFFIX}
>>>>> > +
-DLLVM_ENABLE_WERROR=${LLVM_ENABLE_WERROR}
>>>>> > +               -DPACKAGE_VERSION=${PACKAGE_VERSION}
>>>>> > +               -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
>>>>> > +
-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
>>>>>
>>>>> How did you decide which variables need to be passed
through like this?
>>>>> The set seems somewhat arbitrary, but I may be missing
something
>>>>> obvious.
>>>>>
>>>>> >                 ${ARG_CMAKE_ARGS}
>>>>> >                 ${PASSTHROUGH_VARIABLES}
>>>>> >      INSTALL_COMMAND ""
>>>>> > @@ -152,7 +165,7 @@
>>>>> >      ExternalProject_Add_Step(${name} force-rebuild
>>>>> >        COMMAND ${run_build}
>>>>> >        COMMENT "Forcing rebuild of ${name}"
>>>>> > -      DEPENDEES configure clean
>>>>> > +      DEPENDEES configure ${always_clean}
>>>>>
>>>>> I'm not sure I understand what this does. If I had to
guess I'd say that
>>>>> when ALWAYS_CLEAN is passed the rebuild of the external
project always
>>>>> invokes clean first, but if it's not passed we'll
just invoke the
>>>>> external build and allow it to be incremental if
appropriate. Is that
>>>>> right?
>>>>>
>>>>> >        DEPENDS ${ALWAYS_REBUILD} ${ARG_DEPENDS}
${TOOLCHAIN_BINS}
>>>>> >        ${cmake_3_4_USES_TERMINAL} )
>>>>> >    endif()
>>>>> > Index: CMakeLists.txt
>>>>> >
==================================================================>>>>>
> --- CMakeLists.txt
>>>>> > +++ CMakeLists.txt
>>>>> > @@ -720,6 +720,8 @@
>>>>> >    add_subdirectory(tools)
>>>>> >  endif()
>>>>> >
>>>>> > +add_subdirectory(runtimes)
>>>>> > +
>>>>> >  if( LLVM_INCLUDE_EXAMPLES )
>>>>> >    add_subdirectory(examples)
>>>>> >  endif()
>>>>> > @@ -730,7 +732,8 @@
>>>>> >      llvm_ExternalProject_Add(test-suite
${LLVM_MAIN_SRC_DIR}/projects/test-suite
>>>>> >        USE_TOOLCHAIN
>>>>> >        EXCLUDE_FROM_ALL
>>>>> > -      NO_INSTALL)
>>>>> > +      NO_INSTALL
>>>>> > +      ALWAYS_CLEAN)
>>>>> >    endif()
>>>>> >    add_subdirectory(test)
>>>>> >    add_subdirectory(unittests)
>>>>> >
>>>>>
>>>>> _______________________________________________
>>>>> llvm-commits mailing list
>>>>> llvm-commits at lists.llvm.org <mailto:llvm-commits at
lists.llvm.org>
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits>
>>>>
>>>>
>>>> _______________________________________________
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lists.llvm.org>
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>
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>>> _______________________________________________
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>>
>
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> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
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