[LLVMdev] compiler-rt CMake build

[Alexey Samsonov]

Hm, this thread:
http://cmake.3232098.n2.nabble.com/ExternalProject-Add-Automatic-Incremental-Rebuilds-Add-Sources-to-IDE-td7585544.html
suggests that ExternalProject is not good at all for tracking source file
changes, and suggests to use add_subdirectory approach and pass
information around in variables. Looks like we just can't express rules
like "use this just-built compiler to build those libraries" in terms of
CMake *sigh*
We can try to configure new build trees with CMake manually, though,
similar to the way it's done in add_tablegen() macro.


On Fri, Feb 21, 2014 at 6:49 PM, Alexey Samsonov <samsonov at google.com>wrote:

> Hi Brad,
>
> I have a few questions regarding ExternalProject_Add. For me it doesn't
> really work as expected.
> I add the following code to the tools/clang/runtime/CMakeLists.txt to
> configure compiler-rt as external project:
>
>   ExternalProject_Add(compiler-rt
>
>     #DEPENDS clang clang++ llvm-config
>
>     PREFIX ${CMAKE_BINARY_DIR}/projects/compiler-rt
>     SOURCE_DIR ${COMPILER_RT_SRC_ROOT}
>
>     CMAKE_ARGS -DCMAKE_C_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/clang
>
>                -DCMAKE_CXX_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++
>
>                -DCMAKE_BUILD_TYPE=Release
>
>
>  -DLLVM_CONFIG_PATH=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-config
>
>
>  -DCOMPILER_RT_OUTPUT_DIR=${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}
>
>
>  -DCOMPILER_RT_INSTALL_PATH=lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}
>
>                # -DCOMPILER_RT_INCLUDE_TESTS=ON
>
>     INSTALL_COMMAND ""
>
>     )
>   add_dependencies(compiler-rt clang clang++ llvm-config)
>
> 1) Looks like "DEPENDS" option is just broken - docs here (
> http://www.kitware.com/media/html/BuildingExternalProjectsWithCMake2.8.html
> )
> state that you can pass CMake targets there, but if I uncomment that line,
> I get errors like:
>
> CMake Error at
> /usr/local/share/cmake-2.8/Modules/ExternalProject.cmake:720 (message):
>   External project "clang" has no stamp_dir
> Call Stack (most recent call first):
>   /usr/local/share/cmake-2.8/Modules/ExternalProject.cmake:932
> (ExternalProject_Get_Property)
>   /usr/local/share/cmake-2.8/Modules/ExternalProject.cmake:1488
> (_ep_get_step_stampfile)
>   /usr/local/share/cmake-2.8/Modules/ExternalProject.cmake:1702
> (_ep_add_configure_command)
>   tools/clang/runtime/CMakeLists.txt:18 (ExternalProject_Add)
>
> as if "clang" was supposed to be another external project. FTR, I use
> cmake 2.8.10.2.
>
> 2) The dependencies don't act as expected: if I run "make compiler-rt", it
> builds Clang, uses it to configure
> compiler-rt and builds compiler-rt. But if I then change the Clang
> sources, and re-run "make compiler-rt",
> Clang is re-built, but compiler-rt is *not* re-configured or re-built,
> while I definitely want this.
>
> 3) The same doc (
> http://www.kitware.com/media/html/BuildingExternalProjectsWithCMake2.8.html)
> states that
> "One drawback, however, is ExternalProject’s lack of full dependency
> analysis. Changes in header files of an external project may
> not cause an incremental rebuild of the affected sources that depend on
> those headers."
> Looks like even if I modify *sources* under projects/compiler-rt, and
> re-run "make compiler-rt" from the build
> directory, it doesn't re-build the compiler-rt libraries. This makes
> incremental development simply impossible.
>
> What am I doing wrong?
>
> On Fri, Feb 7, 2014 at 1:59 AM, Brad King <brad.king at kitware.com> wrote:
>
>> On 02/06/2014 01:02 PM, Alexey Samsonov wrote:
>> > OK, I feel like I need to learn more about ExternalProject_Add magic.
>>
>> It is the CMake equivalent to a configure+make build target that
>> runs configure+make for another project.
>>
>> > I have a few quick questions for people with knowledge - currently:
>> > 1) "compiler-rt"'s CMake needs to know about targets in the Clang build
>> tree ("clang") and
>> > in LLVM build tree ("FileCheck", llvm-* command-line tools, googletest
>> etc.), and uses common
>> > macro from LLVM's CMake modules like "configute_lit_site_cfg",
>> "parse_arguments".
>>
>> This will be possible once LLVM and Clang are taught to provide proper
>> content in LLVMConfig.cmake and ClangConfig.cmake package configuration
>> files.  The patch series I proposed in the thread Greg linked at the
>> start of this thread is the first step to do that.
>>
>> > 2) top-level targets from compiler-rt's CMake files are visible at the
>> root of LLVM's build tree,
>> > so that I can run "make check-asan" or even "make clang_rt.asan-x86_64"
>> from the root of
>> > the build tree.
>>
>> This would not work with ExternalProject_Add because the CMake
>> running on LLVM or Clang would not see the targets in compiler-rt
>> since the project will not even be processed until build (make) time.
>> In return the compiler-rt would be able to build using the just-built
>> Clang because it will now be available when CMake runs on compiler-rt.
>> (IIUC this is currently the case for configure+make.)  Also compiler-rt
>> could now be built outside of a LLVM/Clang that was built unaware of
>> compiler-rt.
>>
>> It is also possible to make project/compiler-rt build optionally
>> with add_subdirectory instead of ExternalProject_Add, as it does now,
>> with the cost of not using the just-built Clang.
>>
>
> --
> Alexey Samsonov, MSK
>



-- 
Alexey Samsonov, MSK
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