979c275097
The module currently stores the target triple as a string. This means that any code that wants to actually use the triple first has to instantiate a Triple, which is somewhat expensive. The change in #121652 caused a moderate compile-time regression due to this. While it would be easy enough to work around, I think that architecturally, it makes more sense to store the parsed Triple in the module, so that it can always be directly queried. For this change, I've opted not to add any magic conversions between std::string and Triple for backwards-compatibilty purses, and instead write out needed Triple()s or str()s explicitly. This is because I think a decent number of them should be changed to work on Triple as well, to avoid unnecessary conversions back and forth. The only interesting part in this patch is that the default triple is Triple("") instead of Triple() to preserve existing behavior. The former defaults to using the ELF object format instead of unknown object format. We should fix that as well.
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.