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Flang is a Fortran compiler targeting LLVM.
We have mailing lists for announcements and developers. Here's the link with the sign-up information:
http://lists.flang-compiler.org/mailman/listinfo
We have a flang-compiler channel on Slack. Slack is invitation only but anyone can join. Here's the link:
https://join.slack.com/t/flang-compiler/shared_invite/MjExOTEyMzQ3MjIxLTE0OTk4NzQyNzUtODQzZWEyMjkwYw
We build Flang on Intel x86-64 and OpenPOWER hardware running either Ubuntu or Red Hat.
Building LLVM requires fairly modern compiler toolchain and CMake, check Getting started with LLVM and Building LLVM with CMake for the full list.
LLVM openmp-llvm modified clang The latest supported LLVM version is 5.0. Flang also supports LLVM version 4.0. To use 4.0, substitute 40 for 50 in the build instructions.
Custom install location The command-line examples provided below will install everything into the default system location.
To specify a custom install location, add -DCMAKE_INSTALL_PREFIX=<INSTALL_PREFIX> to each of the CMake commands given below.
When using a custom install location, you must make sure that the bin directory is on your PATH when building and running flang.
Flang is developed outside of the llvm source tree.
Get LLVM 5.0, build and install it according to instructions
cd where/you/want/to/build
git clone https://github.com/llvm-mirror/llvm.git
cd llvm
git checkout release_50
mkdir build && cd build
cmake ..
make
sudo make install
Get the modified clang for flang, build and install it (4.0)
cd where/you/want/to/build
git clone https://github.com/flang-compiler/clang.git
cd clang
git checkout flang_release_50
mkdir build && cd build
cmake ..
make
sudo make install
If you use CMAKE_INSTALL_PREFIX in Step 1 and <INSTALL_PREFIX>/bin is not in your path, you need to add -DLLVM_CONFIG=<INSTALL_PREFIX>/bin/llvm-config when invoking CMake, otherwise you will encounter an error related to LLVMConfig.cmake not being found.
Build and install openmp-llvm (5.0)
cd where/you/want/to/build
git clone https://github.com/llvm-mirror/openmp.git
cd openmp/runtime
git checkout release_50
mkdir build && cd build
cmake ..
make
sudo make install
Build and install the flang components
cd where/you/want/to/build
git clone https://github.com/flang-compiler/flang.git
cd flang
mkdir build && cd build
cmake -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_Fortran_COMPILER=flang ..
make
sudo make install
If you use CMAKE_INSTALL_PREFIX in Step 1 and <INSTALL_PREFIX>/bin is not in your path, you need to add -DLLVM_CONFIG=<INSTALL_PREFIX>/bin/llvm-config and set the explicit paths for the compilers (i.e. -DCMAKE_CXX_COMPILER=<INSTALL_PREFIX>/bin/clang++ -DCMAKE_C_COMPILER=<INSTALL_PREFIX>/bin/clang -DCMAKE_Fortran_COMPILER=<INSTALL_PREFIX>/bin/flang) when invoking CMake, otherwise you will encounter errors.
Spack is a flexible package manager for HPC system and can be used to build flang and its dependencies.
Get Spack
git clone https://github.com/llnl/spack.git
On bash:
source spack/share/spack/setup-env.sh
or tcsh:
source spack/share/spack/setup-env.csh
Build Flang and its depencencies:
spack install flang
watch out for the installation path, the flang wrapper script in there is ready to use.
(optional) setup Flang as a compiler inside spack if you want to build spack package with flang:
spack compiler add path/to/flang/bin
Now you might want to edit your ~/.spack/*/compilers.yaml to combine flang with any c compiler of your choice.
To test your installation, create a simple "hello world" program, like the following:
program hello
print *, 'hello world'
end
Next, compile the program in the following manner. We will assume the program is called hello.f90
% flang hello.f90
If the build succeeds, then you can execute the program in the following manner:
% ./a.out
For a list of compiler options, enter
% flang -help
The Flang compiler supports accepts all clang 4.0 compiler options and supports many, as well as the following flang-specific compiler options:
- -noFlangLibs Do not link against Flang libraries
- -mp Enable OpenMP and link with with OpenMP library libomp
- -nomp Do not link with OpenMP library libomp
- -Mbackslash Treat backslash character like a C-style escape character
- -Mno-backslash Treat backslash like any other character
- -Mbyteswapio Swap byte-order for unformatted input/output
- -Mfixed Assume fixed-format source
- -Mextend Allow source lines up to 132 characters
- -Mfreeform Assume free-format source
- -Mpreprocess Run preprocessor for Fortran files
- -Mrecursive Generate code to allow recursive subprograms
- -Mstandard Check standard conformance
- -Msave Assume all variables have SAVE attribute
- -module path to module file (-I also works)
- -Mallocatable=95 Select Fortran 95 semantics for assignments to allocatable objects (Default)
- -Mallocatable=03 Select Fortran 03 semantics for assignments to allocatable objects
- -static-flang-libs Link using static Flang libraries
- -M[no]daz Treat denormalized numbers as zero
- -M[no]flushz Set SSE to flush-to-zero mode
- -Mcache_align Align large objects on cache-line boundaries
- -M[no]fprelaxed This option is ignored
- -fdefault-integer-8 Treat INTEGER and LOGICAL as INTEGER8 and LOGICAL8
- -fdefault-real-8 Treat REAL as REAL*8
- -i8 Treat INTEGER and LOGICAL as INTEGER8 and LOGICAL8
- -r8 Treat REAL as REAL*8
- -fno-fortran-main Don't link in Fortran main