[llvm-dev] LLVM build performance with LLVM

[Itaru Kitayama via llvm-dev]

As I am facing the serious super slow down:
https://bugs.llvm.org/show_bug.cgi?id=44407 , I'd like to
learn more about how it can be minimized. When debugging an app, there are
times building it with a
Debug build LLVM can not be avoided, but a situation like 40 times time
increase (40 minutes) is hard
to work with.


On Fri, Jan 3, 2020 at 11:14 AM David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Thu, Jan 2, 2020 at 6:09 PM Itaru Kitayama <itaru.kitayama at gmail.com>
> wrote:
>
>> David,
>> Yes, I was indeed trying to build LLVM with a Debug build. I'll stop
>> doing that from now on.
>>
>
> I mean, you can - it's just going to be super slow & mostly not what you
> want, unless you're trying to debug that building process. Usually you'd
> want to isolate one particular test case, maybe even reduce it, before
> running it with a debug build of LLVM which will be quite slow (because
> it's not optimized at all).
>
>
>> I am on JSC's JURON machine which has 251 GB of memory on the login node,
>> that's more than sufficient
>> to do a build, I suppose, and the linker is LLD as LLVM has a CMake
>> variable to select the linker.
>>
>
> Yep, sounds like you're just tripping over the fact that an
> unoptimized/debug build of LLVM is very slow. *thumbs up*
>
>
>>
>> On Fri, Jan 3, 2020 at 11:02 AM David Blaikie <dblaikie at gmail.com> wrote:
>>
>>> Were you trying to use a Debug build to build LLVM? Yes, that would be
>>> very slow.
>>>
>>> If you mean you were using a release build of LLVM to build a Debug
>>> build of LLVM - yeah, that's generally going to be recommended. Did this
>>> get slower/change significantly in performance? Many people have trouble
>>> with building Debug builds (no matter the host compiler) especially if
>>> they're using bfd-ld, since it's quite slow/uses a lot of memory. There are
>>> a few other issues to do with memory usage (do you have less than about a
>>> GB of RAM per CPU? Then you'll probably hit swapping by default & have a
>>> bad time - there are ways around that)
>>>
>>>
>>> On Thu, Jan 2, 2020 at 5:42 PM Itaru Kitayama via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Hi,
>>>> When building LLVM, is it always recommended to do it with the
>>>> latest official release, currently, it is 9.0.1? I ask because when I
>>>> tried
>>>> it with a Debug build, it took an enormous amount of time on POWER8.
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>
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