[llvm-dev] Beginning developer questions

[David Blaikie via llvm-dev]

On Tue, Jan 12, 2021 at 7:35 AM Deep Majumder via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Thanks everyone for the advice! I am able to build LLVM now without
> causing my laptop to thrash. Also as I understand that for auto-complete in
> LLVM, Linux is not the best place to be. Also, thanks for the
> Doxygen-generated docs link.
> Warm regards,
>

If you're more vim/emacs than IDE - I use
https://wiki.archlinux.org/index.php/Vim/YouCompleteMe and
compile_commands.json generated from the ninja build I think (maybe it's
generated by cmake? I forget)


> Deep
>
> On Tue, Jan 12, 2021 at 10:03 AM Craig Topper <craig.topper at gmail.com>
> wrote:
>
>>
>> On Mon, Jan 11, 2021 at 8:07 PM Stefanos Baziotis via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi Deep,
>>>
>>> 1) Kind of. There's Doxygen generated from source automatically, which
>>> shows you many things e.g., members of a type along with some short
>>> documentation (which is taken from the code). It also shows you the
>>> inheritance tree related to this type
>>> Here's an example: https://llvm.org/doxygen/classllvm_1_1LoopInfo.html
>>> It doesn't really matter what this is for now, but you can see e.g.,
>>> that LoopInfo inherits from LoopInfoBase. If you scroll down, you can click
>>> to different members and go to a more detailed description further down.
>>> You can open the dropdown menus (e.g., public
>>> functions inherited). And finally, at the top, you can see the file it
>>> appears at. In general, I think that if you start clicking stuff, it's
>>> going to make sense, it's relatively intuitive.
>>>
>>> 2) Try minimizing the number of parallel threads used. I think by
>>> default Ninja uses all the available threads which in most machines will
>>> fill up the RAM. To limit them, use the -j argument like this: ninja -j8
>>> Another thing that will probably be useful in general is that you can
>>> choose to build specific sub-projects instead of building the whole thing,
>>> like this: ninja -j8 opt
>>>
>>
>> You can also use -DLLVM_PARALLEL_LINK_JOBS=<number> on your cmake
>> command to limit just the number of linking jobs that can run in parallel.
>> -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON can be a useful
>> build configuration that you gets you debug logging and assertions, but you
>> won't have debug symbols for gdb. There's also -DLLVM_USE_SPLIT_DWARF. All
>> of these options are covered here
>> https://llvm.org/docs/GettingStarted.html#common-problems
>>
>>
>>>
>>> 3) Ok, first of all, if you only care about editing and not debugging
>>> LLVM (i.e. launching it with a debugger like gdb), then editors like Vim,
>>> Emacs, 4coder, maybe Sublime Text should do the job. I think most people
>>> developing LLVM on Linux use something like this.
>>>
>>> Now, if you're interested in IDEs and / or debuggers, well, the news in
>>> Linux is bad IMHO. For example, in my machine, GDB takes _30 seconds_ to
>>> launch the debug build of opt.
>>> So, I couldn't use any IDE because virtually all use GDB under the hood.
>>> Personally, I switched to Windows + Visual Studio just for this reason.
>>> That was an insane productivity boost for me.
>>> But if you need something that works in Linux, you can maybe try LLDB.
>>> Hopefully it will be faster. If yes, you can maybe try hooking it in an
>>> IDE, which I guess won't be trivial.
>>>
>>> That said, as I don't develop LLVM in Linux, other people might have
>>> better suggestions.
>>>
>>> Best,
>>> Stefanos
>>>
>>> Στις Τρί, 12 Ιαν 2021 στις 5:43 π.μ., ο/η Deep Majumder via llvm-dev <
>>> llvm-dev at lists.llvm.org> έγραψε:
>>>
>>>> Hello everyone,
>>>> I have been studying the LLVM IR and now want to get into LLVM
>>>> development. I have a few questions regarding that and I would be really
>>>> grateful to get answers for:
>>>>
>>>> 1) The LangRef is an excellent guide/reference to the IR. Is there
>>>> something similar for the codebase (the core llvm to be specific)? Or do I
>>>> have to generate that from the source, in which case how do I do that?
>>>> 2) I tried building just the llvm sub-project, and that is filling up
>>>> my RAM completely during the linking stages, and sends my laptop thrashing.
>>>> I am using Ninja. Is there a way to mitigate this? (I am on Ubuntu 20.04
>>>> Linux, 8 GM RAM, 8 GM swap on an HDD).
>>>> 3) VSCode, at least on my laptop, is very sluggish with such large a
>>>> project. Is there any recommended development environment for Linux (or at
>>>> least something that has been found to work well)?
>>>>
>>>> Thank you for your time!
>>>> Regards,
>>>> Deep
>>>> _______________________________________________
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>>>> llvm-dev at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>> _______________________________________________
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