2080334574
This PR is to improve the driver code to build `flang-rt` path by re-using the logic and code of `compiler-rt`. 1. Moved `addFortranRuntimeLibraryPath` and `addFortranRuntimeLibs` to `ToolChain.h` and made them virtual so that they can be overridden if customization is needed. The current implementation of those two procedures is moved to `ToolChain.cpp` as the base implementation to default to. 2. Both AIX and PPCLinux now override `addFortranRuntimeLibs`. The overriding function of `addFortranRuntimeLibs` for both AIX and PPCLinux calls `getCompilerRTArgString` => `getCompilerRT` => `buildCompilerRTBasename` to get the path to `flang-rt`. This code handles `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR` setting. As shown in `PPCLinux.cpp`, `FT_static` is the default. If not found, it will search and build for `FT_shared`. To differentiate `flang-rt` from `clang-rt`, a boolean flag `IsFortran` is passed to the chain of functions in order to reach `buildCompilerRTBasename`.
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.