[flang-commits] [flang] [Flang] Add FIR and LLVM lowering support for prefetch directive (PR #167272)

[Tom Eccles via flang-commits]

https://github.com/tblah approved this pull request.

LGTM if tests pass.

As a nit, please add a comment above the prefetch op explaining the need for the allocation effect. Perhaps something like
> The allocation effect is to ensure this operation is not removed by dead code elimination as a dead read on the argument: the prefetch happens as a side effect.

https://github.com/llvm/llvm-project/pull/167272