F18 is a ground-up implementation of a Fortran front end written in modern C++. F18, when combined with LLVM, is intended to replace the Flang compiler.
Flang is a Fortran compiler targeting LLVM. Visit the Flang wiki for more information about Flang.
Read more about f18 in the documentation directory. Start with the compiler overview.
To better understand Fortran as a language and the specific grammar accepted by f18, read Fortran For C Programmers and f18'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 an f18 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 f18 uses modern C++ features.
cd where/you/want/the/source git clone https://github.com/flang-compiler/f18.git
F18 is written in C++17.
The code has been compiled and tested with GCC versions 7.2.0, 7.3.0, 8.1.0, and 8.2.0.
The code has been compiled and tested with clang version 7.0 and 8.0 using either GNU‘s libstdc++ or LLVM’s libc++.
F18 uses components from LLVM.
The instructions to build LLVM can be found at https://llvm.org/docs/GettingStarted.html.
We highly recommend using the same compiler to compile both llvm and f18.
The f18 CMakeList.txt file uses the variable LLVM_DIR to find the installed LLVM components and the variable MLIR_DIR to find the installed MLIR components.
To get the correct LLVM and MLIR libraries included in your f18 build, define LLVM_DIR and MLIR_DIR on the cmake command line.
LLVM=<LLVM_BUILD_DIR>/lib/cmake/llvm \ MLIR=<LLVM_BUILD_DIR>/lib/cmake/mlir \ cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ...
where LLVM_BUILD_DIR is the top-level directory where LLVM was built.
If you do not want to build Fortran IR, add -DLINK_WITH_FIR=Off to f18 cmake command and ignore the rest of this section.
If you intend to build f18 with Fortran IR (-DLINK_WITH_FIR On by default), you must:
-DCMAKE_CXX_STANDARD=17 -DLLVM_ENABLE_PROJECTS="mlir" to LLVM cmake command.make install in order to get the required AddMLIR cmake file (it is not generated in LLVM build directory).Installing LLVM from packages is most likely not an option as it will not include MLIR and not be built following C++17 standard.
MLIR is under active development and the most recent development version may be incompatible. A branch named f18 is available inside LLVM fork in https://github.com/flang-compiler/f18-llvm-project. It contains a version of LLVM that is known be compatible to build f18 with FIR.
The fastest way to get set up is to do:
cd where/you/want/to/build/llvm
git clone --depth=1 -b f18 https://github.com/flang-compiler/f18-llvm-project.git
mkdir build
mkdir install
cd build
cmake ../f18-llvm-project/llvm -DCMAKE_BUILD_TYPE=Release \
-DLLVM_ENABLE_PROJECTS=mlir -DCMAKE_CXX_STANDARD=17 \
-DLLVM_INSTALL_UTILS=On \
-DCMAKE_INSTALL_PREFIX=../install
make
make install
Then, -DLLVM_DIR would have to be set to <where/you/want/to/build/llvm>/install/lib/cmake/llvm and, -DMLIR_DIR would have to be set to <where/you/want/to/build/llvm>/install/lib/cmake/mlir
in f18 cmake command.
To run lit tests, -DLLVM_EXTERNAL_LIT=<where/you/want/to/build/llvm>/build/bin/llvm-lit must be added to f18 cmake command. This is because llvm-lit is not part of LLVM installation.
Note that when using some advanced options from f18 cmake file it may be necessary to reproduce their effects in LLVM cmake command.
By default, cmake will search for g++ on your PATH. The g++ version must be one of the supported versions in order to build f18.
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.
export CXX=g++-8.3
or
CXX=/opt/gcc-8.3/bin/g++-8.3 cmake ...
To build f18 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.
export CXX=clang++
To specify a custom install location, add -DCMAKE_INSTALL_PREFIX=<INSTALL_PREFIX> to the cmake command where <INSTALL_PREFIX> is the path where f18 should be installed.
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.
cd ~/f18/build cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/f18/src make
To run all tests:
cd ~/f18/build cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/f18/src make test check-all
To run individual regression tests llvm-lit needs to know the lit configuration for f18. The parameters in charge of this are: flang_site_config and flang_config. And they can be set as shown bellow:
<path-to-llvm-lit>/llvm-lit \ --param flang_site_config=<path-to-f18-build>/test-lit/lit.site.cfg.py \ --param flang_config=<path-to-f18-build>/test-lit/lit.cfg.py \ <path-to-fortran-test>
If f18 was built with -DLINK_WITH_FIR=On (On by default), it is possible to generate FIR language documentation by running make flang-doc. This will create docs/Dialect/FIRLangRef.md in f18 build directory.