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.

Configure, build, and install

libclc is built as part of an LLVM runtimes build.

Select the targets to build with LLVM_RUNTIME_TARGETS, and enable libclc for each selected target with the matching RUNTIMES_<target-triple>_LLVM_ENABLE_RUNTIMES cache entry.

Configure for the AMDGPU target

cd llvm-project
mkdir build
cd build
cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Release \
  -DRUNTIMES_amdgcn-amd-amdhsa-llvm_LLVM_ENABLE_RUNTIMES=libclc \
  -DLLVM_RUNTIME_TARGETS="amdgcn-amd-amdhsa-llvm"

Configure for the NVPTX64 target

cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Release \
  -DRUNTIMES_nvptx64-nvidia-cuda_LLVM_ENABLE_RUNTIMES=libclc \
  -DLLVM_RUNTIME_TARGETS="nvptx64-nvidia-cuda"

Configure for CLSPV targets

cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Release \
  -DRUNTIMES_clspv--_LLVM_ENABLE_RUNTIMES=libclc \
  -DRUNTIMES_clspv64--_LLVM_ENABLE_RUNTIMES=libclc \
  -DLLVM_RUNTIME_TARGETS="clspv--;clspv64--"

Configure for SPIR-V targets

cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Release \
  -DRUNTIMES_spirv-mesa3d-_LLVM_ENABLE_RUNTIMES=libclc \
  -DRUNTIMES_spirv64-mesa3d-_LLVM_ENABLE_RUNTIMES=libclc \
  -DLLVM_RUNTIME_TARGETS="spirv-mesa3d-;spirv64-mesa3d-"

To build multiple targets, pass them as a semicolon-separated list in LLVM_RUNTIME_TARGETS and provide a matching RUNTIMES_<target-triple>_LLVM_ENABLE_RUNTIMES=libclc entry for each target.

Build

ninja

Install

ninja install

Note you can use the DESTDIR Makefile variable to do staged installs.

DESTDIR=/path/for/staged/install ninja install

Run tests

ninja check-libclc-<target-triple>

ninja -C runtimes/runtimes-<target-triple>-bins check-libclc

Out-of-tree build

To build out of tree, or in other words, against an existing LLVM build or install:

CC=$(<path-to>/llvm-config --bindir)/clang cmake \
  <path-to>/llvm-project/libclc/CMakeLists.txt -DCMAKE_BUILD_TYPE=Release \
  -G Ninja -DLLVM_DIR=$(<path-to>/llvm-config --cmakedir) \
  -DLLVM_RUNTIMES_TARGET=<target-triple>
$ ninja

Then install as before.

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.

Website

https://libclc.llvm.org/