Extract Flang's runtime library to use the LLVM_ENABLE_RUNTIME
mechanism. It will only become active when
`LLVM_ENABLE_RUNTIMES=flang-rt` is used, which also changes the
`FLANG_INCLUDE_RUNTIME` to `OFF` so the old runtime build rules do not
conflict. This also means that unless `LLVM_ENABLE_RUNTIMES=flang-rt` is
passed, nothing changes with the current build process.
Motivation:
* Consistency with LLVM's other runtime libraries (compiler-rt, libc,
libcxx, openmp offload, ...)
* Allows compiling the runtime for multiple targets at once using the
LLVM_RUNTIME_TARGETS configuration options
* Installs the runtime into the compiler's per-target resource directory
so it can be automatically found even when cross-compiling
Also see RFC discussion at
https://discourse.llvm.org/t/rfc-use-llvm-enable-runtimes-for-flangs-runtime/80826
Following the conclusion of the
[RFC](https://discourse.llvm.org/t/rfc-names-for-flang-rt-libraries/84321),
rename Flang's runtime libraries as follows:
* libFortranRuntime.(a|so) to libflang_rt.runtime.(a|so)
* libFortranFloat128Math.a to libflang_rt.quadmath.a
* libCufRuntime_cuda_${CUDAToolkit_VERSION_MAJOR}.(a|so) to
libflang_rt.cuda_${CUDAToolkit_VERSION_MAJOR}.(a|so)
This follows the same naming scheme as Compiler-RT libraries
(`libclang_rt.${component}.(a|so)`). It provides some consistency
between Flang's runtime libraries for current and potential future
library components.
I changed the set of files that are built for experimental CUDA/OMP
builds, i.e. the files with enabled device support are built
as such and the rest of the files are built just for the host target.
With this change we can build Flang runtime library that is fully functional
on the host target, so in-tree targets like check-flang become operational.
Reviewed By: klausler, PeteSteinfeld
Differential Revision: https://reviews.llvm.org/D155029
These are initial changes to experiment with building the Fortran runtime
as a CUDA or OpenMP target offload library.
The initial patch defines a set of macros that have to be used consistently
in Flang runtime source code so that it can be built for different
offload devices using different programming models (CUDA, HIP, OpenMP target
offload). Currently supported modes are:
* CUDA: Flang runtime may be built as a fatlib for the host and a set
of CUDA architectures specified during the build. The packaging
of the device code is done by the CUDA toolchain and may differ
from toolchan to toolchain.
* OpenMP offload:
- host_device mode: Flang runtime may be built as a fatlib for the host
and a set of OpenMP offload architectures. The packaging
of the device code is done by the OpenMP offload compiler and may differ
from compiler to compiler.
OpenMP offload 'nohost' mode is a TODO to match the build setup
of libomptarget/DeviceRTL. Flang runtime will be built as LLVM Bitcode
library using Clang/LLVM toolchain. The host part of the library
will be "empty", so there will be two distributable object: the host
Flang runtime and dummy host library with device Flang runtime pieces
packaged using clang-offload-packager and clang.
In all supported modes, enabling parts of Flang runtime for the device
compilation can be done iteratively to make the patches observable.
Note that at any point in time the resulting library may have unresolved
references to not yet enabled parts of Flang runtime.
Example cmake/make commands for building with Clang for NVPTX target:
cmake \
-DFLANG_EXPERIMENTAL_CUDA_RUNTIME=ON \
-DCMAKE_CUDA_ARCHITECTURES=80 \
-DCMAKE_C_COMPILER=/clang_nvptx/bin/clang \
-DCMAKE_CXX_COMPILER=/clang_nvptx/bin/clang++ \
-DCMAKE_CUDA_COMPILER=/clang_nvptx/bin/clang \
/llvm-project/flang/runtime/
make -j FortranRuntime
Example cmake/make commands for building with Clang OpenMP offload:
cmake \
-DFLANG_EXPERIMENTAL_OMP_OFFLOAD_BUILD="host_device" \
-DCMAKE_C_COMPILER=clang \
-DCMAKE_CXX_COMPILER=clang++ \
-DFLANG_OMP_DEVICE_ARCHITECTURES="sm_80" \
../flang/runtime/
make -j FortranRuntime
Differential Revision: https://reviews.llvm.org/D151173
