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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.
Flang
Flang is a ground-up implementation of a Fortran front end written in modern C++. It started off as the f18 project (https://github.com/flang-compiler/f18) with an aim to replace the previous flang project (https://github.com/flang-compiler/flang) and address its various deficiencies. F18 was subsequently accepted into the LLVM project and rechristened as Flang.
Please note that flang is not ready yet for production usage.
Getting Started
Read more about flang in the docs directory. Start with the compiler overview.
To better understand Fortran as a language and the specific grammar accepted by flang, read Fortran For C Programmers and flang's specifications of the Fortran grammar and the OpenMP grammar.
Treatment of language extensions is covered in this document.
To understand the compilers handling of intrinsics, see the discussion of intrinsics.
To understand how a flang program communicates with libraries at runtime, see the discussion of runtime descriptors.
If you're interested in contributing to the compiler, read the style guide and also review how flang uses modern C++ features.
If you are interested in writing new documentation, follow LLVM's Markdown style guide.
Consult the Getting Started with Flang for information on building and running flang.