b2bdd8bd39
Some libclc builtins currently use internal builtins prefixed with '__clc_' for various reasons, e.g., to avoid naming clashes. This commit formalizes this concept by starting to isolate the definitions of these internal clc builtins into a separate self-contained bytecode library, which is linked into each target's libclc OpenCL builtins before optimization takes place. The goal of this step is to allow additional libraries of builtins that provide entry points (or bindings) that are not written in OpenCL C but still wish to expose OpenCL-compatible builtins. By moving the implementations into a separate self-contained library, entry points can share as much code as possible without going through OpenCL C. The overall structure of the internal clc library is similar to the current OpenCL structure, with SOURCES files and targets being able to override the definitions of builtins as needed. The idea is that the OpenCL builtins will begin to need fewer target-specific overrides, as those will slowly move over to the clc builtins instead. Another advantage of having a separate bytecode library with the CLC implementations is that we can internalize the symbols when linking it (separately), whereas currently the CLC symbols make it into the final builtins library (and perhaps even the final compiled binary). This patch starts of with 'dot' as it's relatively self-contained, as opposed to most of the maths builtins which tend to pull in other builtins. We can also start to clang-format the builtins as we go, which should help to modernize the codebase.
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.