[Openmp-dev] Offloading application build with a Trunk Debug Clang is so slow

[Itaru Kitayama via Openmp-dev]

On POWER8, my app builds 40 minutes with the Debug Clang (40 times increase
of time, when
it is built with Release Clang), but on an x86 host, it just takes about 10
minutes and it is bearable.

Could this be PowerPC specific, is it why most people aren't aware of the
slowness?


On Thu, Dec 19, 2019 at 1:38 PM Itaru Kitayama <itaru.kitayama at gmail.com>
wrote:

> Trunk Clang built with setting both variables to
> -DCMAKE_BUILD_TYPE=Release -DLIBOMPTARGET_ENABLE_DEBUG=False
> builds my application in a minute or so.
>
> On Thu, Dec 19, 2019 at 8:18 AM Itaru Kitayama <itaru.kitayama at gmail.com>
> wrote:
>
>> The CMake was executed as below:
>>
>> cmake -GNinja -DCMAKE_BUILD_TYPE=Debug -DLIBOMPTARGET_ENABLE_DEBUG=True
>> -DCMAKE_INSTALL_PREFIX=$SCRATCH/pcp0151/opt/clang/${today}
>> -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
>> -DGCC_INSTALL_PREFIX=/gpfs/software/opt/gcc/7.2.0/
>> -DLLVM_ENABLE_PROJECTS="clang;openmp;libcxx;libcxxabi;lld"
>> -DCLANG_OPENMP_NVPTX_DEFAULT_ARCH=sm_60
>> -DLIBOMPTARGET_NVPTX_COMPUTE_CAPABILITIES=60
>> -DLLVM_TARGETS_TO_BUILD="PowerPC;NVPTX"
>> $SCRATCH/pcp0151/projects/llvm-project/llvm
>>
>> On Thu, Dec 19, 2019 at 7:57 AM Itaru Kitayama <itaru.kitayama at gmail.com>
>> wrote:
>>
>>> The Clang at this commit:
>>> commit 1c49553c19a7044fbbf4528b732926f19f210e54
>>> Author: Bjorn Pettersson <bjorn.a.pettersson at ericsson.com>
>>> Date:   Thu Dec 12 20:51:13 2019 +0100
>>> [kitayama1 at juron1-adm pcp0151]$ time clang++ -g -fopenmp
>>> -fopenmp-targets=nvptx64 mini.cpp
>>>
>>> real 0m2.344s
>>> user 0m2.231s
>>> sys 0m0.049s
>>> Release Clang 9
>>> [[kitayama1 at juron1-adm pcp0151]$ time clang++ -g -fopenmp
>>> -fopenmp-targets=nvptx64 mini.cpp
>>>
>>> real 0m0.693s
>>> user 0m0.533s
>>> sys 0m0.047s
>>>
>>> On Thu, Dec 19, 2019 at 5:32 AM Jon Chesterfield <
>>> jonathanchesterfield at gmail.com> wrote:
>>>
>>>> Ah, OK. In that case I still suspect a regression in clang, as opposed
>>>> to a change in the library. Does the compile time remain very slow if you
>>>> roll deviceRTL back by a few days?
>>>>
>>>> On Wed, Dec 18, 2019 at 8:30 PM Itaru Kitayama <
>>>> itaru.kitayama at gmail.com> wrote:
>>>>
>>>>> Sorry, of course it should include this #pragma
>>>>> omp target parallel for for(;;) {}. My local Debug Clang is updated
>>>>> daily, so the tool chain is pretty much up to date.
>>>>>
>>>>> On Thu, Dec 19, 2019 at 5:24 Jon Chesterfield <
>>>>> jonathanchesterfield at gmail.com> wrote:
>>>>>
>>>>>> On Wed, Dec 18, 2019 at 8:13 PM Itaru Kitayama <
>>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>>
>>>>>>> The app build time increases can be reproduced with a simple int
>>>>>>> main() {} code.
>>>>>>>
>>>>>>
>>>>>> I thought the problem was with the compile time of deviceRTL.
>>>>>>
>>>>>> If you're compiling int main() {}, then there's no openmp involved,
>>>>>> so that seems out of scope for this list.
>>>>>>
>>>>>>
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