Interplay of LCG_DICT_HEADER and LCG_DICT_XML with ALPAKA_BACKENDS

[makortel]

It seems that if a data format package BuildFile.xml specifies explicitly the classes.h headers and the classes_def.xml selection XML files like here

cmssw/DataFormats/ParticleFlowReco/BuildFile.xml

Lines 20 to 21 in c56dd8a

	<flags LCG_DICT_HEADER="classes_1.h classes_2.h"/>
	<flags LCG_DICT_XML="classes_def_1.xml classes_def_2.xml"/>

and one enables the Alpaka backend compilation with <flags ALPAKA_BACKENDS="1"/>, the src/alpaka/classes_<backend>.h and src/alpaka/classes_<backend>.def.xml files are not being considered.

[makortel]

assign core,heterogeneous

[cmsbuild]

New categories assigned: heterogeneous,core

@fwyzard,@Dr15Jones,@smuzaffar,@makortel,@makortel you have been requested to review this Pull request/Issue and eventually sign? Thanks

[cmsbuild]

A new Issue was created by @makortel Matti Kortelainen.

@Dr15Jones, @perrotta, @dpiparo, @rappoccio, @makortel, @smuzaffar can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[makortel]

@smuzaffar Just as a guess we tried

 <flags LCG_DICT_HEADER="classes_1.h classes_2.h alpaka/classes_serial.h alpaka/classes_cuda.h"/> 
 <flags LCG_DICT_XML="classes_def_1.xml classes_def_2.xml alpaka/classes_serial_def.xml alpaka/classes_cuda_def.xml"/> 

but that didn't work either. I'm not sure if that would even be a good way to declare the classes* files inside the alpaka subdirectory.

[smuzaffar]

@makortel , yes this is known issue with the build rules. I already have it on my to do list to fix it but did not realized that we will hit it this soon :-)
Currently, alpaka backend rules do not support multiple HEADER/XML files. I will update the rules to not consider LCG_DICT_HEADER/XML for alpaka backend and use default classes_(serial|cuda).h files for backend. If we need to support multiple header/def files for each alpaka backend too then I guess we can support something like

 <flags LCG_DICT_HEADER="classes_1.h classes_2.h"/> 
 <flags LCG_DICT_XML="classes_def_1.xml classes_def_2.xml"/> 
 <flags ALPAKA_SERIAL_LCG_DICT_HEADER="classes_serial_1.h classes_serial_2.h"/> 
 <flags ALPAKA_SERIAL_LCG_DICT_XML="classes_serial_def_1.xml classes_def_serial_2.xml"/> 
 <flags ALPAKA_CUDA_LCG_DICT_HEADER="classes_cuda_1.h classes_cuda_2.h"/> 
 <flags ALPAKA_CUDA_LCG_DICT_XML="classes_cuda_def_1.xml classes_def_cuda_2.xml"/> 

[makortel]

In this specific case the Alpaka backend's did not need to be split in multiple files. I'd also expect that in the near-to-medium term we would not really need the ability (but for long term it could be useful). The problem was that already the presence of LCG_DICT_HEADER and LCG_DICT_XML (or because they had two elements?) seemed to prevent the generation of dictionaries for each Alpaka backend.

As a quick workaround we merged the classes_{1,2}.h and classes_def_{1,2}.xml in the developers area so that he was able to continue his work.

[smuzaffar]

yes presence of LCG_DICT_HEADER/XML was feeding the wrong information to alpaka backend rules. One reason we had split these files was to avoid long rootcling/compilation times. Multiple files allowed the build system to run rootcling and compilation in parallel.

[makortel]

@smuzaffar Could you remind me if this issue was fixed?

[smuzaffar]

No, not yet @makortel

[makortel]

Ok. There is now a PR merging two classes_def_<N>.xml files together to work around the problem #42807 .

[smuzaffar]

@makortel , cms-sw/cmsdist#8705 addresses this issue. It should allow multiple header/xml files for alpaka backend too.