llvm dev - Jan 2020 - LLVM build performance with LLVM

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.
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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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David,
Yes, I was indeed trying to build LLVM with a Debug build. I'll stop doing
that from now on.

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.

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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