Add GPU annotations to LFRic infrastructure

[Sergi Siso (sergisiso)]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: Oakley Brunt (@oakleybrunt)

To improve GPU coverage in LFRic, the infrastructure and global variables used inside kernels also need to be annotated with omp declare target directives. These directives cannot currently be added by PSyclone because the relevant files are either not provided to it or are not yet preprocessed when PSyclone runs.

This limitation will be resolved once the new LFRic build system is introduced, but until then, adding the directives directly in the code is the most practical solution for the work we do to support Hacka Fett (@christophermaynard) GIG.

The directives will be ignored by any other compiler, and I can open an issue to remove these once the new build system and PSyclone functionality allow them to be added automatically.

I also modified the flags in nvfortran.mk to make the GPU output numerically equivalent to the CPU (with the same compiler) to make it easier to validate.

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• I have tested this change locally, using the LFRic Core rose-stem suite
• If required (e.g. API changes) I have also run the LFRic Apps test suite using this branch
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
• I have added tests to cover new functionality as appropriate (e.g. system tests, unit tests, etc.)
• Any new tests have been assigned an appropriate amount of compute resource and have been allocated to an appropriate testing group (i.e. the developer tests are for jobs which use a small amount of compute resource and complete in a matter of minutes)

trac.log

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

Performance Impact

• Performance of the code has been considered and, if applicable, suitable performance measurements have been conducted

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the TCD Team

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• CLA compliance has been confirmed
• Code quality standards have been met
• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[Thomas Bendall (tommbendall)]

No complaints from a code owner point-of-view