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262 lines
8.0 KiB
262 lines
8.0 KiB
# Flang
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Flang is a ground-up implementation of a Fortran front end written in modern
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C++. It started off as the f18 project (https://github.com/flang-compiler/f18)
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with an aim to replace the previous flang project
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(https://github.com/flang-compiler/flang) and address its various deficiencies.
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F18 was subsequently accepted into the LLVM project and rechristened as Flang.
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## Getting Started
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Read more about flang in the [docs directory](docs).
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Start with the [compiler overview](docs/Overview.md).
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To better understand Fortran as a language
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and the specific grammar accepted by flang,
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read [Fortran For C Programmers](docs/FortranForCProgrammers.md)
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and
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flang's specifications of the [Fortran grammar](docs/f2018-grammar.md)
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and
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the [OpenMP grammar](docs/OpenMP-4.5-grammar.md).
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Treatment of language extensions is covered
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in [this document](docs/Extensions.md).
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To understand the compilers handling of intrinsics,
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see the [discussion of intrinsics](docs/Intrinsics.md).
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To understand how a flang program communicates with libraries at runtime,
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see the discussion of [runtime descriptors](docs/RuntimeDescriptor.md).
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If you're interested in contributing to the compiler,
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read the [style guide](docs/C++style.md)
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and
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also review [how flang uses modern C++ features](docs/C++17.md).
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If you are interested in writing new documentation, follow
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[markdown style guide from LLVM](https://github.com/llvm/llvm-project/blob/master/llvm/docs/MarkdownQuickstartTemplate.md).
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## Supported C++ compilers
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Flang is written in C++17.
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The code has been compiled and tested with
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GCC versions from 7.2.0 to 9.3.0.
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The code has been compiled and tested with
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clang version 7.0, 8.0, 9.0 and 10.0
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using either GNU's libstdc++ or LLVM's libc++.
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The code has been compiled on
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AArch64, x86\_64 and ppc64le servers
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with CentOS7, Ubuntu18.04, Rhel, MacOs, Mojave, XCode and
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Apple Clang version 10.0.1.
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The code does not compile with Windows and a compiler that does not have
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support for C++17.
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## Building Flang out of tree
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These instructions are for building Flang separately from LLVM; if you are
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building Flang alongside LLVM then follow the standard LLVM build instructions
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and add flang to `LLVM_ENABLE_PROJECTS` instead, as detailed there.
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### LLVM dependency
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The instructions to build LLVM can be found at
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https://llvm.org/docs/GettingStarted.html. If you are building flang as part
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of LLVM, follow those instructions and add flang to `LLVM_ENABLE_PROJECTS`.
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We highly recommend using the same compiler to compile both llvm and flang.
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The flang CMakeList.txt file uses
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the variable `LLVM_DIR` to find the installed LLVM components
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and
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the variable `MLIR_DIR` to find the installed MLIR components.
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To get the correct LLVM and MLIR libraries included in your flang build,
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define LLVM_DIR and MLIR_DIR on the cmake command line.
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```
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LLVM=<LLVM_BUILD_DIR>/lib/cmake/llvm \
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MLIR=<LLVM_BUILD_DIR>/lib/cmake/mlir \
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cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ...
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```
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where `LLVM_BUILD_DIR` is
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the top-level directory where LLVM was built.
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### Building flang with GCC
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By default,
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cmake will search for g++ on your PATH.
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The g++ version must be one of the supported versions
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in order to build flang.
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Or, cmake will use the variable CXX to find the C++ compiler. CXX should include
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the full path to the compiler or a name that will be found on your PATH, e.g.
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g++-8.3, assuming g++-8.3 is on your PATH.
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```
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export CXX=g++-8.3
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```
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or
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```
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CXX=/opt/gcc-8.3/bin/g++-8.3 cmake ...
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```
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### Building flang with clang
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To build flang with clang,
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cmake needs to know how to find clang++
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and the GCC library and tools that were used to build clang++.
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CXX should include the full path to clang++
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or clang++ should be found on your PATH.
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```
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export CXX=clang++
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```
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### Installation Directory
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To specify a custom install location,
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add
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`-DCMAKE_INSTALL_PREFIX=<INSTALL_PREFIX>`
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to the cmake command
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where `<INSTALL_PREFIX>`
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is the path where flang should be installed.
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### Build Types
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To create a debug build,
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add
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`-DCMAKE_BUILD_TYPE=Debug`
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to the cmake command.
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Debug builds execute slowly.
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To create a release build,
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add
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`-DCMAKE_BUILD_TYPE=Release`
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to the cmake command.
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Release builds execute quickly.
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### Build Flang out of tree
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```
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cd ~/flang/build
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cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
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make
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```
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### Build The New Flang Driver
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The new Flang driver, `flang-new`, is currently under active development and
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should be considered as an experimental feature. For this reason it is disabled
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by default. This will change once the new driver replaces the _throwaway_
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driver, `flang`.
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In order to build the new driver, add `-DFLANG_BUILD_NEW_DRIVER=ON` to your
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CMake invocation line. Additionally, when building out-of-tree, use `CLANG_DIR`
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(similarly to `LLVM_DIR` and `MLIR_DIR`) to find the installed Clang
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components.
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**Note:** `CLANG_DIR` is only required when building the new Flang driver,
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which currently depends on Clang.
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# How to Run Tests
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Flang supports 2 different categories of tests
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1. Regression tests (https://www.llvm.org/docs/TestingGuide.html#regression-tests)
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2. Unit tests (https://www.llvm.org/docs/TestingGuide.html#unit-tests)
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## For out of tree builds
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To run all tests:
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```
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cd ~/flang/build
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cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
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make test check-all
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```
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To run individual regression tests llvm-lit needs to know the lit
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configuration for flang. The parameters in charge of this are:
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flang_site_config and flang_config. And they can be set as shown below:
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```
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<path-to-llvm-lit>/llvm-lit \
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--param flang_site_config=<path-to-flang-build>/test-lit/lit.site.cfg.py \
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--param flang_config=<path-to-flang-build>/test-lit/lit.cfg.py \
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<path-to-fortran-test>
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```
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Unit tests:
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If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`ON` by default), it is possible to generate unittests.
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Note: Unit-tests will be skipped for LLVM install for an out-of-tree build as it does not include googletest related headers and libraries.
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There are various ways to run unit-tests.
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```
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1. make check-flang-unit
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2. make check-all or make check-flang
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3. <path-to-llvm-lit>/llvm-lit \
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test/Unit
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4. Invoking tests from <out-of-tree flang build>/unittests/<respective unit test folder>
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```
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## For in tree builds
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If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`On` by default), it is possible to
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generate unittests.
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To run all of the flang unit tests use the `check-flang-unit` target:
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```
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make check-flang-unit
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```
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To run all of the flang regression tests use the `check-flang` target:
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```
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make check-flang
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```
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# How to Generate Documentation
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## Generate FIR Documentation
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If flang was built with `-DLINK_WITH_FIR=On` (`On` by default), it is possible to
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generate FIR language documentation by running `make flang-doc`. This will
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create `docs/Dialect/FIRLangRef.md` in flang build directory.
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## Generate Doxygen-based Documentation
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To generate doxygen-style documentation from source code
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- Pass `-DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON` to the cmake command.
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```
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cd ~/llvm-project/build
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cmake -DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON ../llvm
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make doxygen-flang
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```
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It will generate html in
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```
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<build-dir>/tools/flang/docs/doxygen/html # for flang docs
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```
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## Generate Sphinx-based Documentation
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<!TODO: Add webpage once we have a website.
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!>
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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
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is mostly meant to be processed by the Sphinx documentation generation
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system to create HTML pages which would be hosted on the webpage of flang and
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updated periodically.
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If you would like to generate and view the HTML locally:
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- Install [Sphinx](http://sphinx-doc.org/), including the [sphinx-markdown-tables](https://pypi.org/project/sphinx-markdown-tables/) extension.
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- Pass `-DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF` to the cmake command.
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```
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cd ~/llvm-project/build
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cmake -DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF ../llvm
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make docs-flang-html
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```
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It will generate html in
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```
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$BROWSER <build-dir>/tools/flang/docs/html/
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```
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