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@jeanPerier explained the importance of converting box loads and stores into `memcpy`s instead of aggregate loads and stores, and I'll do my best to explain it here. * [(godbolt link) Example comparing opt transformations on memcpys vs aggregate load/stores](https://godbolt.org/z/be7xM83cG) * LLVM can more effectively reason about memcpys compared to aggregate load/stores. * This came up when others were discussing array descriptors for assumed-rank arrays passed to `bind(c)` subroutines, with the implication that the array descriptors are known to have lower bounds of 1 and that they are not pointer/allocatable types. * [(godbolt link) Clang also uses memcpys so we should probably follow them, assuming the clang developers are generatign what they know Opt will handle more effectively.](https://godbolt.org/z/YT4x7387W) * This currently may not help much without the `nocapture` attribute being propagated to function calls, but [it looks like someone may do this soon (discourse link)](https://discourse.llvm.org/t/applying-the-nocapture-attribute-to-reference-passed-arguments-in-fortran-subroutines/81401/23) or I can do this in a follow-up patch. Note on test `flang/test/Fir/embox-char.fir`: it looks like the original test was auto-generated. I wasn't too sure which parts were especially important to test, so I regenerated the test. If we want the updated version to look more like the old version, I'll make those changes.
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