[llvm-dev] Beginning developer questions

[Craig Topper via llvm-dev]

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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