================ @@ -0,0 +1,198 @@ +<!--===- README.md + + Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. + See https://llvm.org/LICENSE.txt for license information. + SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception + +--> + +# Fortran Runtime (flang-rt) + +Flang-rt is the runtime library for code emitted by the Flang compiler +(https://flang.llvm.org). + + +## Getting Started + +There are two build modes for the flang-rt. The bootstrap build, also +called the in-tree build, and the runtime-only build, also called the +out-of-tree build. +Not to be confused with the terms +[in-source and out-of-source](https://cmake.org/cmake/help/latest/manual/cmake.1.html#introduction-to-cmake-buildsystems) +builds as defined by CMake. In an in-source build, the source directory and the +build directory are identical, whereas with an out-of-source build the +build artifacts are stored somewhere else, possibly in a subdirectory of the +source directory. LLVM does not support in-source builds. + + +### Requirements + +Requirements: + * [Same as LLVM](https://llvm.org/docs/GettingStarted.html#requirements). + + +### Bootstrap/In-Tree Build + +The bootstrap build will first build Clang and Flang, then use these compilers +to compile flang-rt. CMake will create a secondary build tree in +configured with these just-built compilers. The secondary build will reuse the +same build options (Flags, Debug/Release, ...) as the primary build. It will +also ensure that once built, flang-rt is found by Flang from either +the build- or install-prefix. To enable, add `flang-rt` to +`LLVM_ENABLE_RUNTIMES`: + +```bash +cmake -S <path-to-llvm-project>/llvm \ + -DNinja \ + -DLLVM_ENABLE_PROJECTS=flang \ + -DLLVM_ENABLE_RUNTIMES=flang-rt \ + ... +``` + +It is recommended to enable building OpenMP alongside Flang and flang-rt +as well. This will build `omp_lib.mod` required to use OpenMP from Fortran. +Building Compiler-RT may also be required, particularly on platforms that do +not provide all C-ABI functionality (such as Windows). + +```bash +cmake -S <path-to-llvm-project>/llvm \ + -DNinja \ + -DCMAKE_BUILD_TYPE=Release \ + -DLLVM_ENABLE_PROJECTS="flang;openmp" \ + -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt" \ + ... +``` + +By default, the enabled runtimes will only be built for the host platform +(`-DLLVM_RUNTIME_TARGETS=default`). To add additional targets to support +cross-compilation via `flang-new --target=<target-triple>`, add more triples to +`LLVM_RUNTIME_TARGETS`, such as +`-DLLVM_RUNTIME_TARGETS="default;aarch64-linux-gnu"`. + +After configuration, build, test, and install the runtime(s) via + +```shell +$ ninja flang-rt +$ ninja check-flang-rt +$ ninja install +``` + + +### Runtime-only/Out-of-Tree Build + +Instead of building Clang and Flang from scratch, the Runtime-only build uses +CMake's environment introspection to find a C, C++, and Fortran compiler. The +compiler to be used can be controlled using CMake's standard mechanisms such as +`CMAKE_CXX_COMPILER`, `CMAKE_CXX_COMPILER`, and `CMAKE_Fortran_COMPILER`. +`CMAKE_Fortran_COMPILER` must be `flang-new` built from the same Git commit as +flang-rt to ensure they are using the same ABI. The C and C++ compiler +can be any compiler supporting the same ABI. + +In addition to the compiler, the build be able to find LLVM development tools ---------------- jeanPerier wrote:
```suggestion In addition to the compiler, the build must be able to find LLVM development tools ``` https://github.com/llvm/llvm-project/pull/110217 _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
