[llvm-dev] Beginning developer questions

[Mehdi AMINI via llvm-dev]

On Mon, Jan 11, 2021 at 8:33 PM Craig Topper via llvm-dev <
llvm-dev at lists.llvm.org> 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
>

On top of these, if you're on Linux I found that using LLD (or Gold) as a
linker instead of the default bfd helps a lot with memory consumption
(-DLLVM_ENABLE_LLD=ON)

>
>
>>
>> 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
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
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