# 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. ## Getting Started Read more about flang in the [docs directory](docs). Start with the [compiler overview](docs/Overview.md). To better understand Fortran as a language and the specific grammar accepted by flang, read [Fortran For C Programmers](docs/FortranForCProgrammers.md) and flang's specifications of the [Fortran grammar](docs/f2018-grammar.md) and the [OpenMP grammar](docs/OpenMP-4.5-grammar.md). Treatment of language extensions is covered in [this document](docs/Extensions.md). To understand the compilers handling of intrinsics, see the [discussion of intrinsics](docs/Intrinsics.md). To understand how a flang program communicates with libraries at runtime, see the discussion of [runtime descriptors](docs/RuntimeDescriptor.md). If you're interested in contributing to the compiler, read the [style guide](docs/C++style.md) and also review [how flang uses modern C++ features](docs/C++17.md). If you are interested in writing new documentation, follow [LLVM's Markdown style guide](https://github.com/llvm/llvm-project/blob/main/llvm/docs/MarkdownQuickstartTemplate.md). ## Building flang There are two ways to build flang. The first method is to build it at the same time that you build all of the projects on which it depends. This is called building in tree. The second method is to first do an in tree build to create all of the projects on which flang depends, and then only build the flang code itself. This is called building standalone. Building standalone has the advantage of being smaller and faster. Once you create the base build and base install areas, you can create multiple standalone builds using them. Note that instructions for building LLVM can be found at https://llvm.org/docs/GettingStarted.html. ### Building flang in tree Building flang in tree means building flang along with all of the projects on which it depends. These projects include mlir, clang, flang, and compiler-rt. Note that compiler-rt is only needed to access libraries that support 16 bit floating point numbers. It's not needed to run the automated tests. Here's a complete set of commands to clone all of the necessary source and do the build. First clone the source: ```bash git clone https://github.com/llvm/llvm-project.git my-project ``` Once the clone is complete, execute the following commands: ```bash cd my-project rm -rf build mkdir -p build cd build cmake \ -G Ninja \ ../llvm \ -DCMAKE_BUILD_TYPE=Release \ -DFLANG_ENABLE_WERROR=On \ -DLLVM_ENABLE_ASSERTIONS=ON \ -DLLVM_TARGETS_TO_BUILD=host \ -DCMAKE_INSTALL_PREFIX=$INSTALLDIR -DLLVM_LIT_ARGS=-v \ -DLLVM_ENABLE_PROJECTS="clang;mlir;flang" \ -DLLVM_ENABLE_RUNTIMES="compiler-rt" ninja ``` To run the flang tests on this build, execute the command in the "build" directory: ```bash ninja check-flang ``` Note that these instructions specify flang as one of the projects to build in the in tree build. This is not strictly necessary for subsequent standalone builds, but doing so lets you run the flang tests to verify that the source code is in good shape. ### Building flang standalone To do the standalone build, start by building flang in tree as described above. This build is base build for subsequent standalone builds. Start each standalone build the same way by cloning the source for llvm-project: ```bash git clone https://github.com/llvm/llvm-project.git standalone ``` Once the clone is complete, execute the following commands: ```bash cd standalone base= cd flang rm -rf build mkdir build cd build cmake \ -G Ninja \ -DCMAKE_BUILD_TYPE=Release \ -DFLANG_ENABLE_WERROR=On \ -DLLVM_TARGETS_TO_BUILD=host \ -DLLVM_ENABLE_ASSERTIONS=On \ -DLLVM_BUILD_MAIN_SRC_DIR=$base/build/lib/cmake/llvm \ -DLLVM_LIT_ARGS=-v \ -DLLVM_DIR=$base/build/lib/cmake/llvm \ -DCLANG_DIR=$base/build/lib/cmake/clang \ -DMLIR_DIR=$base/build/lib/cmake/mlir \ .. ninja ``` To run the flang tests on this build, execute the command in the "flang/build" directory: ```bash ninja check-flang ``` ## Supported C++ compilers Flang is written in C++17. The code has been compiled and tested with GCC versions from 7.2.0 to 9.3.0. The code has been compiled and tested with clang version 7.0, 8.0, 9.0 and 10.0 using either GNU's libstdc++ or LLVM's libc++. The code has been compiled on AArch64, x86\_64 and ppc64le servers with CentOS7, Ubuntu18.04, Rhel, MacOs, Mojave, XCode and Apple Clang version 10.0.1. The code does not compile with Windows and a compiler that does not have support for C++17. ### Building flang with GCC By default, cmake will search for g++ on your PATH. The g++ version must be one of the supported versions in order to build flang. Or, cmake will use the variable CXX to find the C++ compiler. CXX should include the full path to the compiler or a name that will be found on your PATH, e.g. g++-8.3, assuming g++-8.3 is on your PATH. ```bash export CXX=g++-8.3 ``` or ```bash CXX=/opt/gcc-8.3/bin/g++-8.3 cmake ... ``` ### Building flang with clang To build flang with clang, cmake needs to know how to find clang++ and the GCC library and tools that were used to build clang++. CXX should include the full path to clang++ or clang++ should be found on your PATH. ```bash export CXX=clang++ ``` ### Installation Directory To specify a custom install location, add `-DCMAKE_INSTALL_PREFIX=` to the cmake command where `` is the path where flang should be installed. ### Build Types To create a debug build, add `-DCMAKE_BUILD_TYPE=Debug` to the cmake command. Debug builds execute slowly. To create a release build, add `-DCMAKE_BUILD_TYPE=Release` to the cmake command. Release builds execute quickly. # How to Run Tests Flang supports 2 different categories of tests 1. Regression tests (https://www.llvm.org/docs/TestingGuide.html#regression-tests) 2. Unit tests (https://www.llvm.org/docs/TestingGuide.html#unit-tests) ## For standalone builds To run all tests: ```bash cd ~/flang/build cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src ninja check-all ``` To run individual regression tests llvm-lit needs to know the lit configuration for flang. The parameters in charge of this are: flang_site_config and flang_config. And they can be set as shown below: ```bash /llvm-lit \ --param flang_site_config=/test-lit/lit.site.cfg.py \ --param flang_config=/test-lit/lit.cfg.py \ ``` Unit tests: If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`ON` by default), it is possible to generate unittests. Note: Unit-tests will be skipped for LLVM install for an standalone build as it does not include googletest related headers and libraries. There are various ways to run unit-tests. ``` 1. ninja check-flang-unit 2. ninja check-all or ninja check-flang 3. /llvm-lit \ test/Unit 4. Invoking tests from /unittests/ ``` ## For in tree builds If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`On` by default), it is possible to generate unittests. To run all of the flang unit tests use the `check-flang-unit` target: ```bash ninja check-flang-unit ``` To run all of the flang regression tests use the `check-flang` target: ```bash ninja check-flang ``` # How to Generate Documentation ## Generate FIR Documentation If flang was built with `-DLINK_WITH_FIR=On` (`On` by default), it is possible to generate FIR language documentation by running `ninja flang-doc`. This will create `docs/Dialect/FIRLangRef.md` in flang build directory. ## Generate Doxygen-based Documentation To generate doxygen-style documentation from source code - Pass `-DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON` to the cmake command. ```bash cd ~/llvm-project/build cmake -DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON ../llvm ninja doxygen-flang ``` It will generate html in ```bash /tools/flang/docs/doxygen/html # for flang docs ``` ## Generate Sphinx-based Documentation Flang documentation should preferably be written in `markdown(.md)` syntax (they can be in `reStructuredText(.rst)` format as well but markdown is recommended in first place), it is mostly meant to be processed by the Sphinx documentation generation system to create HTML pages which would be hosted on the webpage of flang and updated periodically. If you would like to generate and view the HTML locally: - Install [Sphinx](http://sphinx-doc.org/), including the [sphinx-markdown-tables](https://pypi.org/project/sphinx-markdown-tables/) extension. - Pass `-DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF` to the cmake command. ```bash cd ~/llvm-project/build cmake -DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF ../llvm ninja docs-flang-html ``` It will generate html in ```bash $BROWSER /tools/flang/docs/html/ ```