[llvm-dev] Beginning developer questions

Thu Jan 14 18:04:16 PST 2021

Hi David,
Do you use ld, gold or lld as the linker. I am getting an unknown flag
error with lld for the --gdb-index.
Warm regards,
Deep

On Thu, Jan 14, 2021, 11:38 PM David Blaikie <dblaikie at gmail.com> wrote:

> gdb startup time can be reduced significantly by using a linker-generated
> index. Compile with -ggnu-pubnames and link with -Wl,--gdb-index. I use
> this configuration (plus Split DWARF, fwiw) and gdb startup time is only a
> few seconds/quite usabel.
>
> On Thu, Jan 14, 2021 at 9:58 AM Deep Majumder via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi all,
>> As Stefanos had pointed out, GDB takes an awful lot of time to even start
>> on a debug build of an executable (say clang). LLDB works better but still
>> isn't quite smooth to work with (takes a long time to set breakpoints). So
>> what do LLVM devs who use Linux use for debugging, or is Windows the
>> predominant platform of development?
>> Warm regards,
>> Deep
>>
>> On Wed, Jan 13, 2021, 12:26 AM <paul.robinson at sony.com> wrote:
>>
>>> Re CLion:  The LLVM **Project** (presumably meaning the Foundation)
>>> does not pay core developers.  It does pay for some infrastructure staff
>>> IIRC.
>>>
>>> However, the project is primarily funded by commercial companies (you
>>> should be able to find documentation of the contributors on the Foundation
>>> website), so I think on that count it would not qualify for the free CLion.
>>>
>>> --paulr
>>>
>>>
>>>
>>> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Chris
>>> Tetreault via llvm-dev
>>> *Sent:* Tuesday, January 12, 2021 1:34 PM
>>> *To:* Deep Majumder <deep.majumder2019 at gmail.com>; LLVM Dev <
>>> llvm-dev at lists.llvm.org>
>>> *Subject:* Re: [llvm-dev] Beginning developer questions
>>>
>>>
>>>
>>> I’ve had good luck using QTCreator for large C++ projects in the past.
>>> Unlike CLion, QTCreator is actually free. It may be worth taking a look.
>>>
>>>
>>>
>>> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Deep
>>> Majumder via llvm-dev
>>> *Sent:* Tuesday, January 12, 2021 9:52 AM
>>> *To:* Madhur Amilkanthwar <madhur13490 at gmail.com>
>>> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
>>> *Subject:* [EXT] Re: [llvm-dev] Beginning developer questions
>>>
>>>
>>>
>>> Hi Stefanos and Madhur,
>>>
>>> Of course it would be great if LLVM is given licenses by JetBrains as it
>>> would benefit many people(I guess) working on this project who are not
>>> students.
>>>
>>> I am a student and so have a free license anyway.
>>>
>>> Also, thank you David for the link.
>>>
>>> Warm Regards,
>>>
>>> Deep
>>>
>>>
>>>
>>> On Tue, Jan 12, 2021 at 11:17 PM Madhur Amilkanthwar <
>>> madhur13490 at gmail.com> wrote:
>>>
>>> Hi Stefanos,
>>>
>>> Speaking of CLion, their page
>>> <https://urldefense.com/v3/__https:/www.jetbrains.com/community/opensource/*support__;Iw!!JmoZiZGBv3RvKRSx!o9fgR9CoQWXxAdRU22r4DY-KSrkbTejsaB5XNz8OYsjXy2OMnwiMJJnRAMhI8ZF95g$>
>>> says open source projects can qualify for free licenses. I am not sure if
>>> LLVM community qualifies as per the below required qualifications:
>>>
>>>
>>>
>>> *Do not pay their core project developers. *
>>>
>>>    - *Meet the Open Source
>>>    <https://urldefense.com/v3/__https:/opensource.org/docs/osd__;!!JmoZiZGBv3RvKRSx!o9fgR9CoQWXxAdRU22r4DY-KSrkbTejsaB5XNz8OYsjXy2OMnwiMJJnRAMjLa7muLA$>
>>>    definition.*
>>>    -
>>>    - *Are in active development, i.e. new code commits are submitted
>>>    regularly within the past 3 months.*
>>>    -
>>>    - *Do not provide paid versions of open source software or any
>>>    commercial services around the Open Source project (e.g. paid support,
>>>    consulting, etc).*
>>>    -
>>>    - *Are not funded by commercial companies or organizations (NGO,
>>>    educational, research, or governmental).*
>>>    -
>>>    -
>>>
>>>
>>>
>>> On Tue, Jan 12, 2021 at 10:31 PM David Blaikie via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>
>>>
>>> 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
>>> <https://urldefense.com/v3/__https:/wiki.archlinux.org/index.php/Vim/YouCompleteMe__;!!JmoZiZGBv3RvKRSx!o9fgR9CoQWXxAdRU22r4DY-KSrkbTejsaB5XNz8OYsjXy2OMnwiMJJnRAMjo76Zb5w$>
>>> and compile_commands.json generated from the ninja build I think (maybe
>>> it's generated by cmake? I forget)
>>>
>>>
>>> Deep
>>>
>>>
>>>
>>> On Tue, Jan 12, 2021 at 10:03 AM Craig Topper <craig.topper at gmail.com>
>>> wrote:
>>>
>>>
>>>
>>> On Mon, Jan 11, 2021 at 8:07 PM Stefanos Baziotis via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> Hi Deep,
>>>
>>> 1) Kind of. There's Doxygen generated from source automatically, which
>>> shows you many things e.g., members of a type along with some short
>>> documentation (which is taken from the code). It also shows you the
>>> inheritance tree related to this type
>>>
>>> Here's an example: https://llvm.org/doxygen/classllvm_1_1LoopInfo.html
>>> <https://urldefense.com/v3/__https:/llvm.org/doxygen/classllvm_1_1LoopInfo.html__;!!JmoZiZGBv3RvKRSx!o9fgR9CoQWXxAdRU22r4DY-KSrkbTejsaB5XNz8OYsjXy2OMnwiMJJnRAMhTJF2iRQ$>
>>>
>>> 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
>>> <https://urldefense.com/v3/__https:/llvm.org/docs/GettingStarted.html*common-problems__;Iw!!JmoZiZGBv3RvKRSx!o9fgR9CoQWXxAdRU22r4DY-KSrkbTejsaB5XNz8OYsjXy2OMnwiMJJnRAMilZ2oAYA$>
>>>
>>>
>>>
>>>
>>>
>>> 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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>>>
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>>>
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>>>
>>>
>>>
>>> --
>>>
>>> *Disclaimer: Views, concerns, thoughts, questions, ideas expressed in
>>> this mail are of my own and my employer has no take in it. *
>>>
>>> Thank You.
>>> Madhur D. Amilkanthwar
>>>
>>> _______________________________________________
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>>
>
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