[llvm-dev] Can I build llvm with only a handful of source files compiled for debug?

[David Blaikie via llvm-dev]

On Wed, Aug 14, 2019 at 12:22 PM Praveen Velliengiri <
praveenvelliengiri at gmail.com> wrote:

> Regarding resource constraint problems, I didn't build llvm on much
> heavier machine previously, so it is difficult for me to tell whether my
> build is taking longer than expected trivially, fresh build (+ clang, lldb)
> takes time. But rebuild are actually fast.
>

Are you already using split DWARF (& gdb-index)?


> I will use -compress-debug-sections with the full build and rebuilds and
> see how fast it is :)
> Making an assumption here: since debug-info is compressed, i think it may
> cause a overhead for the debugger. Is it true? If so, it overhead is
> observable to some extent ?
>

Compression will add some CPU compile time (& some link time, technically -
since the linker will decompress the sections to link them), but might save
time when writing fewer bytes to disk (& save disk usage). Similarly
decompression by the debugger might slow things, but reading fewer bytes
from disk may speed them up - will depend on the CPU versus disk IO speeds.


>
> On Thu, 15 Aug 2019 at 00:33, David Blaikie <dblaikie at gmail.com> wrote:
>
>> Are you already using split DWARF & still having resource constraint
>> problems? (oh, you could also compress debug info,
>> -Wa,-compress-debug-sections)
>>
>>
>>
>> On Wed, Aug 14, 2019 at 12:00 PM Praveen Velliengiri <
>> praveenvelliengiri at gmail.com> wrote:
>>
>>> Actually, I have same question, If llvm build provides a option similar
>>> to that, it will be lot more easier for people doing development in
>>> relatively less (compute, storage) PC's.
>>>
>>>
>>> On Thu, 15 Aug 2019 at 00:22, David Blaikie via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Nothing supported, though might not be too hard to do by hand.
>>>>
>>>> If you're having long link times, lots of disk usage, and slow gdb
>>>> startup time I'd recommend enabling split DWARF (LLVM_USE_SPLIT_DWARF=ON,
>>>> and CMAKE_EXE_LINKER_FLAGS_*=-Wl,-gdb-index in cmake) if you haven't
>>>> already.
>>>>
>>>> On Wed, Aug 14, 2019 at 11:40 AM Robert Henry via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>> In order to minimize edit/compile/debug turn time, is there a way to
>>>>> compile llvm tools so that the majority of the files are compiled as if for
>>>>> release (eg, no debug symbols), and only the handful of files that I have
>>>>> touched are compiled for debugging? This will reduce the load on the file
>>>>> system, linker and gdb tremendously.  At present, AFAICT, it's all or
>>>>> nothing.
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
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>>>
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