1c6cecdbdd
libclc uses llvm-link to link together all of the individually built libclc builtins files into one module. Some of these builtins files are compiled from source by clang whilst others are converted from LLVM IR directly to bytecode. When llvm-link links a 'source' module into a 'destination' module, it warns if the two modules have differing data layouts. The LLVM IR files libclc links either have no data layout (shared submodule files) or an explicit data layout in the case of certain amdgcn/r600 files. The warnings are very noisy and largely inconsequential. We can suppress them exploiting a specific behaviours exhibited by llvm-link. When the destination module has no data layout, it is given the source module's data layout. Thus, if we link together all IR files first, followed by the clang-compiled modules, 99% of the warnings are suppressed as they arose from linking an empty data layout into a non-empty one. The remaining warnings came from the amdgcn and r600 targets. Some of these were because the data layouts were out of date compared with what clang currently produced, so those could have been updated. However, even with those changes and by grouping the IR files together, the linker may still link explicit data layouts with empty ones depending on the order the IR files are processed. As it happens, the data layouts aren't essential. With the changes to the link line we can rely on those IR files receiving the correct data layout from the clang-compiled modules later in the link line. This also makes the previously AMDGPU-specific IR files available to be used by all targets in a generic capacity in the future.
libclc
libclc is an open source implementation of the library requirements of the OpenCL C programming language, as specified by the OpenCL 1.1 Specification. The following sections of the specification impose library requirements:
- 6.1: Supported Data Types
- 6.2.3: Explicit Conversions
- 6.2.4.2: Reinterpreting Types Using as_type() and as_typen()
- 6.9: Preprocessor Directives and Macros
- 6.11: Built-in Functions
- 9.3: Double Precision Floating-Point
- 9.4: 64-bit Atomics
- 9.5: Writing to 3D image memory objects
- 9.6: Half Precision Floating-Point
libclc is intended to be used with the Clang compiler's OpenCL frontend.
libclc is designed to be portable and extensible. To this end, it provides generic implementations of most library requirements, allowing the target to override the generic implementation at the granularity of individual functions.
libclc currently supports PTX, AMDGPU, SPIRV and CLSPV targets, but support for more targets is welcome.
Compiling and installing
(in the following instructions you can use make or ninja)
For an in-tree build, Clang must also be built at the same time:
$ cmake <path-to>/llvm-project/llvm/CMakeLists.txt -DLLVM_ENABLE_PROJECTS="libclc;clang" \
-DCMAKE_BUILD_TYPE=Release -G Ninja
$ ninja
Then install:
$ ninja install
Note you can use the DESTDIR Makefile variable to do staged installs.
$ DESTDIR=/path/for/staged/install ninja install
To build out of tree, or in other words, against an existing LLVM build or install:
$ cmake <path-to>/llvm-project/libclc/CMakeLists.txt -DCMAKE_BUILD_TYPE=Release \
-G Ninja -DLLVM_DIR=$(<path-to>/llvm-config --cmakedir)
$ ninja
Then install as before.
In both cases this will include all supported targets. You can choose which
targets are enabled by passing -DLIBCLC_TARGETS_TO_BUILD to CMake. The default
is all.
In both cases, the LLVM used must include the targets you want libclc support for
(AMDGPU and NVPTX are enabled in LLVM by default). Apart from SPIRV where you do
not need an LLVM target but you do need the
llvm-spirv tool available.
Either build this in-tree, or place it in the directory pointed to by
LLVM_TOOLS_BINARY_DIR.