Speed-up of adjoint transport

[DrTVockerodtMO]

PR Summary

Sci/Tech Reviewer: @tom-j-h
Code Reviewer: @mo-lottieturner

Includes speed-ups to adjoint transport algorithms and kernels. Main algorithm speedups include removing vestigial setting of internal fields to zero, and then replacing inc_X_plus_Y invokes with setval_x. In the kernels, mostly consists of removing patterns like:

internal_field = 0.0_r_def
...
do idx = loop_min, loop_max
  internal_field = internal_field + <some calculation>
  ...
  internal_field = 0.0_r_def
end do
...

with simply:

do idx = loop_min, loop_max
  internal_field = <some calculation>
  ...
end do

I have also included putting the proper kinds on zero setting as this may trigger implicit float conversions.

• fixes Speed-up adjoint transport (algorithms + kernels) #141

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
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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
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trac.log

Test Suite Results - lfric_apps - lfric_apps_speedup_adj_transport/run1

Suite Information

Item	Value
Suite Name	lfric_apps_speedup_adj_transport/run1
Suite User	terence.vockerodt
Workflow Start	2026-01-15T14:39:30
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2025.12.1	True
jules	MetOffice/jules@2025.12.1	True
lfric_apps	DrTVockerodtMO/lfric_apps@lfric_apps_speedup_adj_transport	False
lfric_core	MetOffice/lfric_core@5d4d72f	True
moci	MetOffice/moci@2025.12.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@2025.12.1	True
socrates	MetOffice/socrates@2025.12.1	True
socrates-spectral	MetOffice/socrates-spectral@2025.12.1	True
ukca	MetOffice/ukca@2025.12.1	True

Task Information

✅ succeeded tasks - 1106

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Performance Impact

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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

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Sci/Tech Review

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

Code Review

• All dependencies have been resolved
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• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[tom-j-h]

Thanks Terry, looks great, just a couple of questions on specific bits.