Optimizations on the loop blocking

[iomaganaris]

• Read neighbors only once for the unrolled loop and then only once for the epilogue loop
• Create as_const_sid for nanobind_adapter to be able to pass the input fields as const and allow the compiler to apply optimizations like avoiding reading vertically independent fields in every k loop iteration (based on Felix's suggestion)
• It was too painful to reuse as_sid from as_const_sid by adding a bool template parameter to as_sid and depending on that call add_const due to the variadic parameters. Maybe try and find a way to make it better?

The idea behind as_const_sid is to be called by the nanobind bindings generated by gt4py only for the input fields. Some extra work is necessary for that.

[fthaler]

Once everything works and is ready, I would actually suggest to open two separate PRs on the main GT repo: one with the SID neighbor table updates and the other one with as_const_sid as both are quite independent.
For as_const_sid a test would also be appreciated.

[fthaler]

Just checked the nanobind documentation and saw that there is a ReadOnly property in the ndarray class (https://nanobind.readthedocs.io/en/latest/api_extra.html#_CPPv4N8nanobind7ndarray8ReadOnlyE). Could it also make sense to just read this property and decide based on this if we should treat the data type as const?

[iomaganaris]

Just checked the nanobind documentation and saw that there is a ReadOnly property in the ndarray class (https://nanobind.readthedocs.io/en/latest/api_extra.html#_CPPv4N8nanobind7ndarray8ReadOnlyE). Could it also make sense to just read this property and decide based on this if we should treat the data type as const?

Good point 👍 I guess something like the last commit together with https://github.com/GridTools/icon_structured_benchmark/compare/main...gtfn_improvements would also make sense? In the bindings I've only added const to the input fields, since the neighbors are going to be automatically turned to const later in as_neighbor_table. We could also just pass them as const from the bindings as well. What do you think?

[iomaganaris]

Superseded by GridTools#1808 and GridTools#1809