[llvm-dev] FYI: Ninja-build user may use CMake-3.9

[NAKAMURA Takumi via llvm-dev]

On Fri, Jul 21, 2017 at 1:16 AM Reid Kleckner <rnk at google.com> wrote:

> This is great news! Do we know who contributed the changes to cut the
> extra library dependencies?
>
> Do you think we should remove ENABLE_OBJLIB to simplify our CMake files in
> the near future? It seems to me that anyone who cares about highly parallel
> build throughput can upgrade CMake to get the good behavior. It's probably
> easier and less error-prone than maintaining a special build configuration.
>

At the moment, this facility (loose deps) is specific to Ninja generator.
There are a couple of users of ENABLE_OBJLIB.
- Tablegen (except for ninja).
- LIBCLANG_BUILD_STATIC. It doesn't use LLVM_ENABLE_OBJLIB, but uses it
internally.

Thanks,
Takumi



> On Thu, Jul 20, 2017 at 8:31 AM, NAKAMURA Takumi via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> This is useful for developer who uses multicore builder.
>> https://cmake.org/cmake/help/v3.9/release/3.9.html#other-changes
>>
>>
>>    - The Ninja
>>    <https://cmake.org/cmake/help/v3.9/generator/Ninja.html#generator:Ninja> generator
>>    has loosened the dependencies of object compilation. Object compilation now
>>    depends only on custom targets and custom commands associated with
>>    libraries on which the object’s target depends and no longer depends on the
>>    libraries themselves. Source files in dependent targets may now compile
>>    without waiting for their targets’ dependencies to link.
>>
>> With BUILD_SHARED_LIBS, compiling units don't wait for preceding shared
>> libs.
>> See also; http://bb.pgr.jp/builders/i686-mingw32-RA-on-linux
>> Regardless of BUILD_SHARED_LIBS, compile units in add_executable() don't
>> wait for preceding libraries,
>> but targets by add_dependencies().
>>
>> It doesn't break anything in llvm tree. Assume;
>>   add_executable(foo foo.cpp)
>>   target_link_libraries(foo LLVMCore) # depends on intrinsics_gen
>> Compiling foo.cpp doesn't wait for LLVMCore, but intrinsics_gen.
>> Linking foo waits for LLVMCore.
>>
>> I have been working for cutting dependencies to increase parallelism.
>> For example, I introduced ENABLE_OBJLIB.
>> See also, https://reviews.llvm.org/rL305635
>> Ninja with CMake-3.9 doesn't require parallelize with objlib.
>>
>> I love ninja-build.
>>
>> Thanks,
>> Takumi
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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