[llvm-dev] Building LLVM through Bazel

[Isaiah Norton via llvm-dev]

>
> 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
>> <https://github.com/tensorflow/tensorflow/blob/efddd17519e43e956c3fa79981c408803521fe61/third_party/llvm/llvm.autogenerated.BUILD#L195>,
>> 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
>>>>
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>>>
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