[llvm-dev] Building LLVM through Bazel

[David Blaikie via llvm-dev]

Yeah, compile_commands.json would be insufficient - it's just the compile
commands, not tblgen. (compile_commands is for clang tools to consume so
they know what command line arguments are used for a given source file, so
they can reproduce that build to show clang-tidy tips, etc)

A log output from something like ninja would likely be complete, I think.

On Thu, Aug 16, 2018 at 1:28 PM Douglas Parker <dgp1130422 at gmail.com> wrote:

> I tried running all the commands in the compile_commands.json (thanks for
> pointing that out), but it runs into the same "No such file or directory:
> *.inc". I don't see those files built anywhere in that list. Does it take
> tblgen into account?
>
> Doug
>
> On Thu, Aug 16, 2018, 1:02 PM Sanjoy Das <sanjoy at playingwithpointers.com>
> wrote:
>
>> TensorFlow uses bazel to build LLVM:
>> https://github.com/tensorflow/tensorflow/tree/master/third_party/llvm
>> The script that generates llvm.autogenerated.BUILD is not open sourced
>> yet unfortunately but looking skimming through the generated file
>> should give you a rough idea of what's involved.
>>
>> -- Sanjoy
>> On Thu, Aug 16, 2018 at 11:16 AM Isaiah Norton via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> >>
>> >> You could look at the cmake+ninja (or other build system) build and
>> dump the commands it executes (I think ninja produces a log, or can do so)
>> which should show you all the commands needed to build any part of LLVM.
>> >
>> >
>> > There's a switch to dump all compiler commands as a JSON file:
>> >
>> >
>> https://cmake.org/cmake/help/v3.12/variable/CMAKE_EXPORT_COMPILE_COMMANDS.html
>> >
>> > On Wed, Aug 15, 2018 at 8:30 PM David Blaikie via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >>
>> >>
>> >>
>> >> On Wed, Aug 15, 2018 at 2:05 PM Douglas Parker <dgp1130422 at gmail.com>
>> wrote:
>> >>>
>> >>> I believe it would be possible to run a cmake command to generate a
>> BUILD file, though I don't know if that would be easier to maintain on the
>> LLVM side. Would definitely be happy to see direct support, though I was
>> just trying to figure out what's needed to hack this together on my end.
>> >>>
>> >>> I guess my real question is what underlying commands are necessary to
>> build all the source files (without actually compiling the C/C++)? If I can
>> understand how to do this manually with terminal/cmake/tblgen, then I could
>> probably get it to work with Bazel.
>> >>>
>> >>> Looking at TensorFlow's setup, it looks like tblgen has dependencies
>> on support which goes down to zlib and gets a lot of complexity there. I
>> get the impression that tblgen isn't so complicated as to require all that.
>> What would be the minimum steps to build tblgen from source?
>> >>
>> >>
>> >> You could look at the cmake+ninja (or other build system) build and
>> dump the commands it executes (I think ninja produces a log, or can do so)
>> which should show you all the commands needed to build any part of LLVM.
>> >>
>> >> But yeah, I think you do have to build support to build tblgen, to run
>> tblgen to generate the rest of the files to continue the build.
>> >>
>> >> - Dave
>> >>
>> >>>
>> >>>
>> >>> Doug
>> >>>
>> >>> On Wed, Aug 15, 2018 at 1:28 PM Chris Bieneman <chris.bieneman at me.com>
>> wrote:
>> >>>>
>> >>>> There have been discussions about adding a Bazel generator before:
>> >>>> https://cmake.org/pipermail/cmake-developers/2017-July/030144.html
>> >>>>
>> >>>> There does seem to be interest in having that support in CMake, and
>> I can't imagine any insurmountable reason why it couldn't be done. The real
>> issue is that nobody has put in the time to do it.
>> >>>>
>> >>>> -Chris
>> >>>>
>> >>>> On Aug 15, 2018, at 11:21 AM, David Blaikie via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >>>>
>> >>>>
>> >>>>
>> >>>> On Wed, Aug 15, 2018 at 10:04 AM Chris Lattner <clattner at nondot.org>
>> wrote:
>> >>>>>
>> >>>>>
>> >>>>>
>> >>>>> > On Aug 14, 2018, at 2:43 PM, David Blaikie via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >>>>> >
>> >>>>> > Yeah - not sure we're quite at the point where LLVM wants to
>> start supporting two build systems again (used to be Configure+Make and the
>> CMake system, now it's just the Cmake system), but if you want to make it
>> work out-of-tree it shouldn't be too difficult (Google does this internally
>> with the internal version of Bazel). Writing a short BUILD extension for
>> running tblgen should be possible without too much complexity - not sure
>> what Tensorflow is doing that makes its solution so complicated, it doesn't
>> seem like it should be terribly hard, just a genrule to run tblgen and
>> generate the appropriate files from the td files.
>> >>>>>
>> >>>>> Would it be technically possible for cmake to generate bazel
>> files?  If so, it seems that that could be a great bridge, and useful to
>> other projects as well.
>> >>>>
>> >>>>
>> >>>> /maybe/? It's an interesting thought - not sure I know enough about
>> either build system to have a very informed opinion here, though.
>> >>>>
>> >>>> - Dave
>> >>>>
>> >>>>>
>> >>>>>
>> >>>>> -Chris
>> >>>>>
>> >>>> _______________________________________________
>> >>>> LLVM Developers mailing list
>> >>>> llvm-dev at lists.llvm.org
>> >>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>>>
>> >>>>
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>> >
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>
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