d5038b3774
This function was already conceptually in the CLC namespace - this just formally moves it over. Note however that this commit marks a change in how libclc functions may be overridden by targets. Until now we have been using a purely build-system-based approach where targets could register identically-named files which took responsibility for the implementation of the builtin in its entirety. This system wasn't well equipped to deal with AMD's overriding of __clc_ldexp for only a subset of types, and furthermore conditionally on a pre-defined macro. One option for handling this would be to require AMD to duplicate code for the versions of __clc_ldexp it's *not* interested in overriding. We could also make it easier for targets to re-define CLC functions through macros or .inc files. Both of these have obvious downsides. We could also keep AMD's overriding in the OpenCL layer and bypass CLC altogether, but this has limited use. We could use weak linkage on the "base" implementations of CLC functions, and allow targets to opt-in to providing their own implementations on a much finer granularity. This commit supports this as a proof of concept; we could expand it to all CLC builtins if accepted. Note that the existing filename-based "claiming" approach is still in effect, so targets have to name their overrides differently to have both files compiled. This could also be refined.
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.