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Developer Guide

Supported Software

oneAPI Construction Kit depends on LLVM and Clang. The compiler information section contains a list of supported versions.

LLVM and Clang need to be built and installed separately. The oneAPI Construction Kit build then uses this installation as a dependency.

Directory layout

Current directory layout:

  • source: Contains source specific to implementing open standards, such as OpenCL and Vulkan.
    • source/cl: Encapsulates all source code which implements the OpenCL open standard, this is an optional component and may not be present dependent on license agreement.
      • source/cl/external/OpenCL-Headers/include: This directory holds the upstream headers in the sub-directory external (for example CL/cl.h).
      • source/cl/source/extension/include: This directory holds the headers for the Codeplay specific OpenCL extensions.
    • source/vk: Encapsulates all source code which implements the Vulkan open standard, this is an optional component and may not be present dependent on license agreement.
  • modules: Contains shared modules used in the implementation of the open standards in source. For details on the modules layout in the modules documentation. Currently we have the following modules:
    • modules/cargo: Generic module containing the implementations of containers.
    • modules/compiler: Module providing the main compilation infrastructure, which in turn contains the following parts:
      • builtins: Module providing the OpenCL C builtins, math library (abacus) and the image library (libimg) are part of this module.
      • cookie contains template files for generating target implementations.
      • targets contains target-specific compilation pipeline infrastructure, including the host device implementation.
      • tools contains the muxc executable.
      • utils contains various common code for transforming IR and metadata.
      • vecz: contains the Vectorizer.
    • modules/mux: Definition of the Mux API.
  • doc: Contains documentation in a structure matching the source and modules directory trees.
  • cmake: Hold various utility CMake scripts.
  • platform: Holds CMake toolchains files for the various supported platforms, as well as all the necessary information to build the oneAPI Construction Kit for the specific platforms.
  • scripts: Holds various scripts used by the oneAPI Construction Kit, includes an OpenCL CTS runner, performance analysis scripts, scripts to help with building, and scripts used in continuous integration.

Branches

The two long running branches are:

  • stable: This branch is merged to on a successful nightly run and should not be merged into directly.
  • main: This is the main branch for on-going development.

No force pushes are allowed on these two branches.

Coding style

C++ Style

All the C++ code in the oneAPI Construction Kit should be formatted using clang-format version 16, and using the .clang-format file provided by the project (option: -style=file).

Header include guards should follow the convention of <MODULE>_<FILE>_H_INCLUDED.

CMake Style

All the CMake scripts in the oneAPI Construction Kit should be free of cmakelint warnings when the following checks are disabled in the .cmakelintrc configuration file:

  • linelength when writing CMake best effort should be made to keep lines shorter than 80 characters, however this is not always practical or possible, the check is disabled.
  • syntax it is possible for cmakelint to generate some false positives when checking CMake syntax, configuring a build with CMake itself is the best method of validating syntax, the check is disabled.
  • convention/filename/package/consistency/package/stdargs these checks are more strict than CMake's documentation suggests, they also trigger warnings in the modules provided by CMake itself, the checks are disabled.

To run cmakelint using the .cmakelintrc configuration file in the root of the oneAPI Construction Kit repository:

$ cmakelint --config=.cmakelintrc <file> [<file>] ...

Python Style

All the Python code in the oneAPI Construction Kit must be formatted using yapf set to the pep8 style (default). As with clang-format it's not perfect in all situations and occasionally does something baffling, but the consistency mostly keeps the holy warriors at bay.

You may also wish to run Python code run through the pylint (configured in .pylintrc) and flake8 linters (configured in .flake8), though these tools can be noisy and encourage somewhat ugly suggestions - so they are not a pre-merge requirement. As with any linter they can catch errors such as use of undefined names - so we encourage that you use them as part of your development flow.

Python code must support Python 3.6.+ version streams. Old code can be updated using the futurize command line tool from the future package to find issues and suggested solutions.

Khronos OpenCL ICD

The Khronos ICD allows multiple OpenCL implementations to coexist in the same system, these implementations will usually be exposed to the OpenCL user as individual cl_platform_id's. To inform the system's OpenCL ICD where to find the oneAPI Construction Kit OpenCL driver it needs to be registered. Note that we also support fetching and building an ICD within the toolkit through cmake options as described here.

Linux Registration

On Linux the ICD looks for all files with the .icd extension in the /etc/OpenCL/vendors directory. To register the oneAPI Construction Kit OpenCL driver issue the following command replacing <install_dir> with the path to the oneAPI Construction Kit install and <bits> bit width of the binary. The command will likely require root privileges.

echo <install_dir>/lib/libCL.so > /etc/OpenCL/vendors/<any_name>.icd

Windows Registration

For Windows the ICD inspects the registry so to register the oneAPI Construction Kit OpenCL driver a new registry entry must be added. Add a REG_DWORD value to the appropriate registry path.

  • 32-bit - HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Khronos\OpenCL\Vendors
  • 64-bit - HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenCL\Vendors

The REG_DWORD value's name should be the path to the oneAPI Construction Kit OpenCL driver and its data should be 0.

Android Registration

To register the oneAPI Construction Kit OpenCL driver with the Android ICD follow the same instructions as Linux except that the directory containing the .icd file should be /system/vendor/Khronos/OpenCL/vendors/.

echo <install_dir>/lib/libCL.so > /system/vendor/Khronos/OpenCL/vendors/<any_name>.icd

Building ICD From Source

In order to test the oneAPI Construction Kit OpenCL driver on systems which do not already have an installed ICD we must first build it from source. Due to the binary redistribution clause in the license oneAPI Construction Kit does not bundle the Khronos ICD, it is however open source and can be cloned then built from the public GitHub repository.

The Khronos ICD does not provide the OpenCL headers files, those are also located on GitHub.

git clone https://github.com/KhronosGroup/OpenCL-ICD-Loader.git
git clone https://github.com/KhronosGroup/OpenCL-Headers.git

The ICD expects to be built against the latest version of the OpenCL headers which at the time of writing is OpenCL 2.2. This is fine since the ICD is backwards compatible. We must symlink or copy the OpenCL headers into the ./inc directory of the ICD repository.

ln -s OpenCL-Headers/opencl22/CL OpenCL-ICD-Loader/inc/CL

Now you can follow the instructions on how to build the ICD as seen in the README.

CMake

Help regarding the CMake options and targets available in the oneAPI Construction Kit when building the project. For advice on modifying the CMake code itself see our CMake Development documentation.

CMake Flags

The flags used when invoking CMake on the command line which are used in the examples shown later in this document.

  • -B<path>: An undocumented option which creates a build directory <path> if it does not already exist then configures the build system in that directory. It is important to specify the source directory position argument otherwise you will see unexpected behaviour.
  • -G<generator>: Specifies the build system generator to use, when not specified the platform specific default generator is used.
  • -D<variable>=<value>: Defines a CMake option stored in CMakeCache.txt to control how CMake configures the build directory.

CMake Options

The builtin CMake options used when invoking CMake on the command line.

  • CMAKE_BUILD_TYPE: CMake provides a default set of build types:
    • Debug: Enable debug symbols and disable optimizations.
    • Release: Enable optimizations and disable assertions.
    • RelWithDebInfo: Enable debug symbols, optimizations, and disable assertions.
    • MinSizeRel: Enable size optimizations and disable assertions.
  • CMAKE_INSTALL_PREFIX: Path to write files produced by the install target.
  • CMAKE_TOOLCHAIN_FILE: Path to a CMake script, used to cross-compile a project, which defines variables that inform CMake where the compiler, assembler, linker, etc. for the target platform reside.

oneAPI Construction Kit CMake Options

  • CMAKE_BUILD_TYPE: In addition to the defaults provided by CMake the oneAPI Construction Kit extends the builtin build types:

    • ReleaseAssert: Enable assertions is a Release build.

  • CA_USE_SANITIZER: Enable support for dynamic analysis sanitizers:

  • CA_LLVM_INSTALL_DIR: Tells the oneAPI Construction Kit to use the LLVM and Clang installation that can be found at this prefix. The LLVM and Clang installations must be development installations i.e. they must contain the relevant llvm headers and support tools, and their version must match a supported LLVM version.

  • CA_ENABLE_API: Semi-colon separated list of APIs to enable. Valid values are cl for OpenCL, and vk for Vulkan. Enabling an API when an optional component is not present dependent on license agreement will result in a CMake error. The default is cl;vk.

  • CA_BUILD_32_BITS: Enable compiling in 32-bit mode on Linux, this requires to have the proper 32-bit toolchain installed. When used in combination with an external LLVM, the external LLVM also needs to be built in 32-bit mode.

  • CA_EXTERNAL_BUILTINS_DIR is used to specify the directory containing pre-generated builtins. This option is mandatory when cross compiling. It is usually set to the modules/builtins directory in the build directory of a host oneAPI Construction Kit build, but can be set to another directory as long as it contains generated builtins.

  • CA_EXTERNAL_BUILTINS: This option is used to specify whether or not builtins should be generated. If it is set to OFF, CA_EXTERNAL_BUILTINS_DIR must be provided to indicate which builtins to use instead. This option is set to ON for cross compile builds.

  • CA_BUILTINS_TOOLS_DIR: This options makes it possible to specify which tools to use in order the build the builtins, executables for the correct versions of clang and llvm-link must be found in this directory. This can also be used for cross-compile builds in which case the tools must work on the host.

  • CA_RUNTIME_COMPILER_ENABLED: This option determines whether the oneAPI Construction Kit is built with or without a runtime compiler (LLVM). It defaults to ON. Without a runtime compiler, only pre-compiled binaries can be run, and the oneAPI Construction Kit implements an embedded profile.

  • CA_CLANG_TIDY_FLAGS: This option specifies a semi-colon separated list of additional flags which are passed to clang-tidy when invoking tidy targets.

  • CA_HOST_ENABLE_BUILTIN_KERNEL: This option enables builtin kernel support within the host target. By default, it is set to OFF. If enabled this will report that host supports builtin kernels and will also enable two test kernels that are used by UnitMux and UnitCL to verify functionality.

  • CA_HOST_ENABLE_FP64: This option determines whether host is built with or without double support. By default, it is only enabled on non-Windows platforms.

  • CA_HOST_ENABLE_FP16: This option determines whether host is built with or without half support. It is disabled by default since we can't detect if this feature is natively supported by hardware, which is a requirement.

  • CA_HOST_ENABLE_PAPI_COUNTERS: This option enables performance counter support in host via the Mux query_pool API and the PAPI performance counter API. Requires the PAPI library and headers to be installed on the system. Currently this only works on Linux.

  • CA_HOST_CROSS_COMPILERS: This option specifies a semi-colon separated list of compilers registered to enable offline or cross-compilation for non-native host CPU's, e.g. for Linux kernel cross-compile arm, aarch64, x86, x86_64 may be specified, alternatively set to all to enable all backends which were built during the LLVM install.

  • CMAKE_SKIP_RPATH: On Linux the oneAPI Construction Kit specifies a relative RPATH for all targets when they are installed using CMAKE_INSTALL_RPATH, this ensures that when the install target is invoked the user does not need to specify LD_LIBRARY_PATH to correctly execute a test binary in order to use the installed OpenCL or Vulkan library. Do disable this behaviour set -DCMAKE_SKIP_RPATH=ON when configuring CMake in build directory.

  • CA_HOST_TARGET_<arch>_CPU: This option is used by the host`` target to optimize for performance on a given CPU. archshould be a capitalized version of thehosttarget architecture e.g.X86_64, RISCV64orAARCH64. If set to "native" host will optimize for the CPU being used to compile it. Otherwise a CPU name can be provided, for example "skylake", but be warned that this string will be passed directly to the llvm backend so make sure it's a valid CPU name. Information about your host CPU can be found by running llc --version, and a list of host CPUs supported by your installed version of LLVM can be found by running llc --march=[your-arch] --mcpu=help`.

    Be aware that if host is compiled with this option set, running it on a different CPU from the one specified (or the one compiled with if "native" was specified) isn't supported and bad things may happen. When the oneAPI Construction Kit is built in debug mode, the environment variable CA_HOST_TARGET_CPU is also respected across all host targets, which can help track down codegen differences among different machine targets. The caveats above apply, and this may result in an illegal instruction crash if your CPU doesn't support the generated instructions.

  • CA_USE_SPLIT_DWARF: When building with gcc, enable split dwarf debuginfo. This significantly reduces binary size (especially when static linking) and speeds up the link step. Requires a non-ancient toolchain.

  • CA_CL_TEST_STATIC_LIB: Forces all of our CL executable targets to link the static CL library rather than the normal dynamic one, to force testing with the static library.

  • CA_MUX_TARGETS_TO_ENABLE: A ; separated list of mux targets that should be enabled. By default this is set to the host target.

  • CA_EXTERNAL_MUX_TARGET_DIRS: A ; separated list of external mux targets that should be built. The base directory name must be that of the target.

  • CA_EXTERNAL_MUX_COMPILER_DIRS: A ; separated list of external compiler targets that should be built. The base directory name must be that of the target.

CMake Build Targets

  • all: The default target, it builds everything which is enabled by default.
  • install: First builds the all target, then installs the files to the path specified by CMAKE_INSTALL_PREFIX.
  • clean: Removes all build artifacts, useful if a file exists which is suspected of being invalid.

oneAPI Construction Kit CMake Build Targets

  • ComputeAorta: Build the OpenCL and Vulkan libraries, if present, and all their test suites.
  • check-ock/check-ock-<target>: Build and run all short running test suites, this selection of testing is used by continuous integration to verify a baseline of correctness, individual test suites can also be tested in isolation by specifying the target to test.
  • internal_builtins: Builds the compiler builtins functions, this target can be used even if automatically building the builtins was disabled with CA_EXTERNAL_BUILTINS, although this target will fail in cross compile builds.
  • doc_html: Generates HTML documentation for the oneAPI Construction Kit project, currently this is only supported for OpenCL. Due to our dependency on the breathe package which has known memory leaks, building this target can take an excessive amount of time or fail with a python MemoryError. A workaround for this issue is to temporarily delete the file api-reference.md to reduce demands on the build.
  • format: When clang-format is found by CMake the format target is added, this target, when invoked, automatically formats all C/C++ source code which has been editing and not yet committed to the repository.
  • tidy/tidy-<target>: When clang-tidy is found by CMake a number of additional targets are added which invoke clang-tidy to perform static analysis. The tidy target runs clang-tidy on all targets adding using the add_ca_{library,exectuable} commands which also add an individual tidy-<target> target per library or executable.
oneAPI Construction Kit OpenCL CMake Build Targets
  • CL: Build only the OpenCL library, only available when OpenCL is enabled.
  • UnitCL: Build the UnitCL test suite, as well as the OpenCL library.
  • OpenCLCTS: Build the OpenCL library and all the CTS binaries.
  • check-ock-cl: Build and run various OpenCL test suites, primarily UnitCL and selected short running OpenCL CTS tests.
oneAPI Construction Kit Vulkan CMake Build Targets
  • VK: Build only the Vulkan library, only available when Vulkan is enabled.
  • UnitVK: Build the UnitVK test suite, as well as the Vulkan library.
  • VKICDManifest: Generates the Vulkan ICD manifest, Linux only.
  • check-ock-vk: Build and run UnitVK and spirv-ll lit tests.

Compiling

Compiling LLVM

oneAPI Construction Kit requires an LLVM install that includes the clang project. First clone the LLVM repository.

git clone https://github.com/llvm/llvm-project.git --branch $LLVMBranch
cd llvm-project

Compiling LLVM from Upstream on Linux

Configure the build directory with CMake, ensuring to enable the clang project using LLVM_ENABLE_PROJECTS. Run this command from the root of the repository.

cmake llvm -GNinja \
  -Bbuild-x86_64 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-x86_64/install \
  -DLLVM_ENABLE_PROJECTS=clang \
  -DLLVM_TARGETS_TO_BUILD='X86;ARM;AArch64'

Now the build directory is configured, build the install target.

ninja -C build-x86_64 install

Compiling LLVM from Upstream on Windows

Configure the build directory with CMake, ensuring to enable the clang project using LLVM_ENABLE_PROJECTS. Run this command from the root of the repository. The LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN variable is needed when building LLVM version 8.0 or later on Visual Studio toolchains prior to MSVC version 19.1.

cmake llvm -G"Visual Studio 15 2017 Win64" ^
  -Bbuild-x86_64 ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCMAKE_INSTALL_PREFIX=%CD%\build-x86_64\install ^
  -DLLVM_TARGETS_TO_BUILD="X86;ARM;AArch64" ^
  -DLLVM_ENABLE_PROJECTS=clang ^
  -DLLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN=ON

Note that using the Ninja generator, -GNinja, on Windows may be preferable for improve compilation times.

Now the build directory is configured, build the install target. This can be done by opening the llvm.sln solution in Visual Studio and building the install target via the GUI for the Release configuration. Alternatively we can build on the command line using CMake as shown below.

cmake --build %CD%\build-x86_64 --target install --config Release

Compiling LLVM-SPIRV

llvm-spirv is used to translate bitcode binaries into SPIR-V binaries.

The SPIRV-LLMV-Translator repository should be cloned into its own directory and not into LLVM's projects sub-directory. In principle, the translator can be cloned into the LLVM source tree and built as yet another LLVM sub-project. However, this currently causes a CMake conflict in the oneAPI Construction Kit on the llvm-spirv executable.

git clone -b llvm_release_80 \
  https://github.com/KhronosGroup/SPIRV-LLVM-Translator.git
cd SPIRV-LLVM-Translator
mkdir build
cd build
cmake .. -GNinja \
  -DLLVM_DIR=/path/to/llvm80/build/install/lib/cmake/llvm/
ninja llvm-spirv

The executable llvm-spirv will be generated in the build/tools/llvm-spirv/ directory.

NOTE: The LLVM release version and the llvm-spirv branch version must match. The vast majority of spir-v binaries have been translated using llvm-spirv based on LLVM 8.0.

Compiling oneAPI Construction Kit

Compiling the oneAPI Construction Kit requires an LLVM install to link against and to use the tools as part of the build process when the runtime compiler is enabled, follow the LLVM guide to build a suitable install. In the following examples the $LLVMInstall variable specifies the directory of the LLVM install. Alternatively, to compile the oneAPI Construction Kit with the runtime compiler disabled follow the without LLVM guide.

The examples provided should be sufficient to get up and running, for more fine grained control of how to compile the oneAPI Construction Kit consult the list of CMake options.

the oneAPI Construction Kit must use the same ``NDEBUG`` configuration as LLVM.
For the most part this should be automatically detected, but if you pass custom
`CXXFLAGS` to cmake, this cannot be properly detected and may cause ABI issues
and subsequent crashes that are difficult to debug

Compiling oneAPI Construction Kit on Linux

To configure the oneAPI Construction Kit build run the following command from the root of the oneAPI Construction Kit repository.

cmake . -GNinja \
  -Bbuild-x86_64 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-x86_64/install \
  -DCA_LLVM_INSTALL_DIR=$LLVMInstall

Now the build directory is configured, build the install target.

ninja -C build-x86_64 install

The check target will run the oneAPI Construction Kit's test suites to ensure the build is working as expected.

ninja -C build-x86_64 check
Compiling Debug oneAPI Construction Kit on Linux

Non-Release build times of the oneAPI Construction Kit can benefit from using a Release install of LLVM, this is because tools such as clang, llvm-dis, FileCheck, and others from a Non-Release LLVM install are used as part of the build. To enable faster build times set the CA_BUILTINS_TOOLS_DIR variable to point to a Release install of LLVM, here $LLVMReleaseInstall specifies the path to the root of the install.

cmake . -GNinja \
  -Bbuild-x86_64-Debug \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-x86_64-Debug/install \
  -DCA_LLVM_INSTALL_DIR=$LLVMInstall \
  -DCA_BUILTINS_TOOLS_DIR=$LLVMReleaseInstall/bin

Now the build directory is configured, you can build the oneAPI Construction Kit and run the dchecks as above.

Compiling oneAPI Construction Kit on Windows

To configure a oneAPI Construction Kit build run the following command from the root of the oneAPI Construction Kit repository.

cmake . -G"Visual Studio 15 2017 Win64" ^
  -Bbuild-x86_64 ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCMAKE_INSTALL_PREFIX=%CD%\build-x86_64\install ^
  -DCA_LLVM_INSTALL_DIR=%LLVMInstall%

Note that using the Ninja generator, -GNinja, on Windows may be preferable for improve compilation times.

Now the build directory is configured, build the install target. This can be done by opening the ComputeAorta.sln solution in Visual Studio and building the install target via the GUI for a Release configuration. Alternatively we can build on the command line using CMake as shown below.

cmake --build %CD%\build-x86_64 --target install --config Release

The check target will run the oneAPI Construction Kit's test suites to ensure the build is working as expected.

cmake --build %CD%\build-x86_64 --target check --config Release

Compiling Debug oneAPI Construction Kit on Windows

Non-Release build times of the oneAPI Construction Kit can benefit from using a Release install of LLVM, this is because tools such as clang, llvm-dis, FileCheck, and others from a Non-Release LLVM install are used as part of the build. To enable faster build times set the CA_BUILTINS_TOOLS_DIR variable to point to a Release install of LLVM, here %LLVMReleaseInstall% specifies the path to the root of the install.

cmake . -G"Visual Studio 15 2017 Win64" ^
  -Bbuild-x86_64-Debug ^
  -DCMAKE_BUILD_TYPE=Debug ^
  -DCMAKE_INSTALL_PREFIX=%CD%\build-x86_64-Debug\install ^
  -DCA_LLVM_INSTALL_DIR=%LLVMInstall% ^
  -DCA_BUILTINS_TOOLS_DIR=%LLVMReleaseInstall%\bin

Note that using the Ninja generator, -GNinja, on Windows may be preferable for improve compilation times.

Now the build directory is configured, you can build the oneAPI Construction Kit and run the checks, changing the --config parameter to Debug.

cmake --build %CD%\build-x86_64-Debug --target install --config Debug
cmake --build %CD%\build-x86_64-Debug --target check --config Debug

Compiling the oneAPI Construction Kit without LLVM

Compiling the oneAPI Construction Kit without LLVM is also referred to as an offline-only configuration or disabling the runtime compiler. In this mode the oneAPI Construction Kit does not include a JIT compiler for OpenCL, offline-only is currently not supported for Vulkan and is disabled in the configuration.

Compiling the oneAPI Construction Kit without LLVM on Linux

The clc offline compiler, which includes LLVM, must be provided. To build clc follow the guide above, the $ONEAPI_CON_KIT_INSTALL variable specifies the path to the root of this install.

To configure the oneAPI Construction Kit build without LLVM run following command from the root of the oneAPI Construction Kit repository.

cmake . -GNinja \
  -Bbuild-offline \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-offline/install \
  -DCA_RUNTIME_COMPILER_ENABLED=OFF \
  -DCA_EXTERNAL_CLC=$ONEAPI_CON_KIT_INSTALL/bin/clc \
  -DCA_ENABLE_API=cl

Now the build directory is configured, build the install target.

ninja -C build-offline install

Compiling oneAPI Construction Kit without LLVM on Windows

The clc offline compiler, which includes LLVM, must be provided. To build clc follow the guide above, the %ONEAPI_CON_KIT_INSTALL% variable specifies the path to the root of this install.

The configure the oneAPI Construction Kit build without LLVM run the following command from the root of the oneAPI Construction Kit repository.

cmake . -G"Visual Studio 15 2017 Win64" ^
  -Bbuild-offline ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCMAKE_INSTALL_PREFIX=%CD%\build-offline\install ^
  -DCA_RUNTIME_COMPILER_ENABLED=OFF ^
  -DCA_EXTERNAL_CLC=%ONEAPI_CON_KIT_INSTALL%\bin\clc ^
  -DCA_ENABLE_API=cl

Now the build directory is configured, build the install target. This can be done by opening the ComputeAorta.sln solution in Visual Studio and building the install target via the GUI for a Release configuration. Alternatively we can build on the command line using CMake as shown below.

cmake --build %CD%\build-offline --target install --config Release

Compiling oneAPI Construction Kit without LLVM on Windows using MinGW

MinGW can be used instead of Visual Studio to compile the oneAPI Construction Kit. On Windows, only offline-only the oneAPI Construction Kit can be built with MinGW, so the build is of limited practical value. The build is configured as follows:

cmake . -GNinja ^
  -DCMAKE_C_COMPILER=gcc.exe ^
  -DCMAKE_CXX_COMPILER=g++.exe ^
  -Bbuild-offline ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCMAKE_INSTALL_PREFIX=%CD%\build-offline\install ^
  -DCA_RUNTIME_COMPILER_ENABLED=OFF ^
  -DCA_CL_ENABLE_OFFLINE_KERNEL_TESTS=OFF ^
  -DCA_ENABLE_API=cl

Then, install with:

cmake --build %CD%\build-offline --target install --config Release

Note: MinGW must be installed with structured exception handling (SEH) and POSIX threads. The choco command is choco install mingw -y -params "/exception:seh /threads:posix".

Cross-compiling

Note: Cross-compilation is only supported on Linux.

Cross-platform building LLVM and oneAPI Construction Kit for Linux

All CMake cross-compilation configurations set CMAKE_TOOLCHAIN_FILE to inform CMake how to compile for the target architecture, this sets up various CMake variables which specify the locations of executables such as the C and C++ compilers, assembler, linker, target file system root, etc.

The examples provided should be sufficient to get up and running, for more fine grained control of how to compile the oneAPI Construction Kit consult the list of CMake options.

Cross-compilation requires -- in most cases -- both a native build of LLVM and a specialised build of of LLVM for the cross-compilation target. In this guide, the following environment variables are assumed.

# path to upstream LLVM build
LLVMNativeBuild=/absolute/path/to/native_llvm/build

# usually equivalent to ${LLVMNativeBuild}/install
LLVMNativeInstall=${CMAKE_INSTALL_PREFIX}

Cross-compiling LLVM

Cross-compiling LLVM from Upstream

To cross-compile LLVM the appropriate CMake toolchain file from the oneAPI Construction Kit repository is required, the path to this will be specified by the $ONEAPI_CON_KIT variable in the following examples.

Cross-compiling LLVM for Arm from Upstream

For cross-compilation targeting Arm only the ARM target back end is enabled. Run the following command to configure an LLVM build targeting Arm from the root of the repository.

cmake . -GNinja \
  -Bbuild-arm \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$ONEAPI_CON_KIT/scripts/toolchains/arm-toolchain.cmake \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-arm/install \
  -DLLVM_TARGET_ARCH=ARM \
  -DLLVM_TARGETS_TO_BUILD=ARM \
  -DLLVM_HOST_TRIPLE=arm-unknown-linux-gnu \
  -DLLVM_DEFAULT_TARGET_TRIPLE=arm-unknown-linux-gnu \
  -DLLVM_ENABLE_ZLIB=OFF \
  -DLLVM_ENABLE_ZSTD=OFF \
  -DLLVM_TABLEGEN=$LLVMNativeInstall/bin/llvm-tblgen \
  -DCLANG_TABLEGEN=$LLVMNativeBuild/bin/clang-tblgen

Now the build directory is configured, build the install target.

ninja -C build-arm install
Cross-compiling LLVM for AArch64 from Upstream

For cross-compilation targeting AArch64 only the AArch64 target back end is enabled. Run the following command to configure an LLVM build targeting Arm from the root of the repository.

cmake . -GNinja \
  -Bbuild-aarch64 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$ONEAPI_CON_KIT/scripts/toolchains/aarch64-toolchain.cmake \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-aarch64/install \
  -DLLVM_TARGET_ARCH=AArch64 \
  -DLLVM_TARGETS_TO_BUILD=AArch64 \
  -DLLVM_HOST_TRIPLE=aarch64-unknown-linux-gnu \
  -DLLVM_DEFAULT_TARGET_TRIPLE=aarch64-unknown-linux-gnu \
  -DLLVM_ENABLE_ZLIB=OFF \
  -DLLVM_ENABLE_ZSTD=OFF \
  -DLLVM_TABLEGEN=$LLVMNativeInstall/bin/llvm-tblgen \
  -DCLANG_TABLEGEN=$LLVMNativeBuild/bin/clang-tblgen

Now the build directory is configured, build the install target.

ninja -C build-aarch64 install

Cross-compiling the oneAPI Construction Kit

Cross-compiling the oneAPI Construction Kit requires a LLVM install to link against, follow the LLVM guide to build a suitable install, the $LLVMInstall variable specifies the path to this install.

oneAPI Construction Kit uses tools from an LLVM install during the build process. For a native x86_64 build no additional install is required, although build times can be improved by doing so. For cross-compilation a native LLVM install is also required, the $LLVMNativeInstall variable specifies the path to this install.

Cross-compiling the oneAPI Construction Kit for Arm

Configure an Arm cross-compile build using the following command.

cmake . -GNinja \
  -Bbuild-arm \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$PWD/platform/arm-linux/arm-toolchain.cmake \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-arm/install \
  -DCA_LLVM_INSTALL_DIR=$LLVMInstall \
  -DCA_BUILTINS_TOOLS_DIR=$LLVMNativeInstall/bin

Now the build directory is configured, build the install target.

ninja -C build-arm install

If qemu-arm is installed on the system arm-toolchain.cmake will automatically detect it and set the CMAKE_CROSSCOMPILING_EMULATOR variable, the oneAPI Construction Kit uses this to enable emulated testing using the check target.

ninja -C build-arm check

Cross-compiling the oneAPI Construction Kit for AArch64

Configure an AArch64 cross-compile build using the following command.

cmake . -GNinja \
  -Bbuild-aarch64 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$PWD/platform/arm-linux/aarch64-toolchain.cmake \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-aarch64/install \
  -DCA_LLVM_INSTALL_DIR=$LLVMInstall \
  -DCA_BUILTINS_TOOLS_DIR=$LLVMNativeInstall/bin

Now the build directory is configured, build the install target.

ninja -C build-aarch64 install

If qemu-aarch64 is installed on the system aarch64-toolchain.cmake will automatically detect it and set the CMAKE_CROSSCOMPILING_EMULATOR variable, the oneAPI Construction Kit uses this to enable emulated testing using the check target.

ninja -C build-aarch64 check

Cross-compiling the oneAPI Construction Kit for Windows with the MinGW toolchain

oneAPI Construction Kit for Windows can be built on Linux using MinGW. This requires LLVM that has been built with MinGW. Note that offline-compiled kernels cannot be built, because there is no way to run the clc that is built.

cmake -GNinja \
  -Bbuild-mingw \
  -DCMAKE_INSTALL_PREFIX=$PWD/build-mingw/install \
  -DCMAKE_TOOLCHAIN_FILE=$PWD/platform/mingw-w64/mingw-w64-toolchain.cmake \
  -DCA_LLVM_INSTALL_DIR=/path/to/mingw/llvm/build \
  -DCMAKE_BUILD_TYPE=ReleaseAssert \
  -DCA_BUILTINS_TOOLS_DIR=/path/to/llvm_tools \
  -DCA_CL_ENABLE_OFFLINE_KERNEL_TESTS=OFF \
  .

cmake --build build-mingw --target ComputeAorta

Testing

Testing OpenCL

  • UnitCL: Is our primary OpenCL test suite, it extensively tests the API part of OpenCL in various situations. It is composed of one self-contained binary. UnitCL also contains a series of kernel execution tests built to test the vectorizer as well as compilation stages. We add regression tests to UnitCL when we fix previously uncaught bugs and when we add new functionality to the oneAPI Construction Kit. See the UnitCL documentation for more details on UnitCL.
  • OpenCL CTS: We have our own runner for the OpenCL CTS, you can refer to its scripts/testing/README.md for how to use it.
  • CLSmith and C-Reduce: CLSmith is a tool to generate random OpenCL kernels, accompanied by a helper application to run them. If a bug is found in a kernel, C-Reduce can help reduce the code size of the test down to a manageable size.

Testing OpenCL with CLSmith

CLSmith is a tool (based on CSmith) used to generate random OpenCL kernels. It also provides a launcher application (cl_launcher) to run the generated kernels and produce an output. Specifically, the output is generated by hashing together all the variables in the kernel.

Build instructions for CLSmith are available on the Github repository. After building it, the easiest way to start using it is with the cl_setup_test.py script found in the scripts directory. The script accepts one argument, a directory name, and it will create that directory in $HOME. In there it will place all the files necessary for creating a running a kernel, such as the CLSmith and cl_launcher executables, as well as some headers required by the generated kernels. So, for example, in order to generate and run a random kernel, one would do the following:

cd CLSmith/scripts
./cl_setup_test.py cltest
cd ~/cltest
./CLSmith
./cl_launcher -f CLProg.c -p 0 -d 0

This will run the random kernel on the first device of the first OpenCL platform (-p 0 -d 0). It is also possible to specify local and global workgroup sizes with the -l and -g arguments, such as

./cl_launcher -f CLProg.c -p 0 -d 0 -l 1,1,1 -g 1,1,1

This will run only one work item, which can help to make the testing faster.

cl_launcher itself is not a testing application, which means that the user can write their own tests around it. For example, a simple test would be to detect if the compilation failed or not. Another test can be constructed by running the kernel on multiple OpenCL implementations and comparing the results. Finally, it is possible to run with and without optimization and compare the results.

Testing OpenCL with C-Reduce

The kernels generated from CLSmith can be hundreds or thousands of lines long, which can make narrowing down the issue difficult. C-Reduce is a tool that can take a source file and a test script and reduce the size of the source file while making sure that the test still fails.

creduce test.sh CLProg.c

C-Reduce is C-aware, using clang to perform C specific changes to the source code. Since clang also supports OpenCL, it is possible to use C-Reduce with OpenCL kernels, although it will not perform OpenCL specific transformation, such as propagation of constant vectors etc.

The first argument for C-Reduce is called the "interestingness" test. This is the test that determines if the transformed source code is still interesting, i.e. if it still exhibits the issue that we are interested in debugging. A simple interestingness test could be the following:

./cl_launcher -f CLProg.c -p 0 -d 0 -l 1,1,1 -g 1,1,1 || return 0

The interestingness test should return 0 if the test is interesting. The test above runs the kernel and if cl_launcher fails for some reason, then it returns 0 (|| is a short-circuited boolean OR in bash). While bash scripts are common, the test can be anything that can be executed, such as python scripts or executables.

C-Reduce is a fairly simple application to use (online documentation), but there are some gotchas:

  1. The input file needs to be given as a relative path, while everything else needs to be in absolute paths. C-Reduce will copy the input file in a temporary directory and work on it from there, so all the paths need to be adjusted accordingly.
  2. Multiple interestingness tests will be run in parallel, so special care needs to be taken when outputting into files etc.
  3. C-Reduce will not do anything other than run the interestingness test to determine whether to keep a transformation or not. This can lead to transformations being applied that produce code that compiles but exhibits undefined behaviour. For this reason, it is also important to incorporate some sort of correctness test in the interestingness test. For example, if testing for runtime failures in OpenCL kernels, it is possible to use tools like Oclgrind to check the kernel for undefined behaviour.
  4. The interestingness test has to be specific, because otherwise it is possible to switch to a different bug during the reduction, or produce code that is completely invalid. For example, it is better to check for a specific output or error message than just a compilation failure in general.
  5. The test should be optimized for performance. During the reduction process, it might be run thousands of times, so if the test is slow the reduction process will also be extremely slow.
  6. When it comes to files generated from CLSmith, it is easier to test them if they are passed though the C preprocessor before testing them, since this will eliminate all the include directives.

Testing oneapi-construction-kit application examples using official Intel oneAPI Base Toolkit

Download the official Intel OneAPI Base Toolkit following the instructions mentioned here.

To compile the tests follow the steps below:

mkdir build_tests
cmake -GNinja -Bbuild_tests -DCMAKE_CXX_COMPILER=/path/to/intel_oneapi/bin/clang++ /path/to/oneapi-construction-kit/examples/applications -DOpenCL_LIBRARY=/path/to/build/lib/libCL.so -DOpenCL_INCLUDE_DIR=/path/to/build-riscv/include
ninja -C build_tests

To test the binaries compiled above, set the environment variables as follows:

export LD_LIBRARY_PATH=/path/to/build/lib:/path/to/intel_oneapi/lib/libsycl.so:/path/to/intel_oneapi/lib:$LD_LIBRARY_PATH
export CMAKE_CXX_COMPILER=/path/to/intel_oneapi/bin/clang++
export CMAKE_C_COMPILER=/path/to/intel_oneapi/bin/clang
export CA_HAL_DEBUG=1
export CA_PROFILE_LEVEL=3
export ONEAPI_DEVICE_SELECTOR=opencl:fpga
export OCL_ICD_FILENAMES=/path/to/build/lib/libCL.so
# As the oneAPI basetoolkit release has a whitelist of devices, it filters out RefSi.
# To override it, as a temporary solution we can point SYCL_CONFIG_FILE_NAME to ``.
# This way it doesn't set the default sycl.conf.
export SYCL_CONFIG_FILE_NAME=""

The tests can be run using ctest command.

cd build_tests
ctest

The generated output should be as follows:

Test project /path/to/build_tests
    Start 1: simple_vector_add
1/7 Test #1: simple_vector_add ..................   Passed    0.06 sec
    Start 2: vector_addition-load-store
2/7 Test #2: vector_addition-load-store .........   Passed    0.04 sec
    Start 3: vector_addition-predicated
3/7 Test #3: vector_addition-predicated .........   Passed    0.03 sec
    Start 4: vector_addition-masked-store
4/7 Test #4: vector_addition-masked-store .......   Passed    0.04 sec
    Start 5: vector_addition-tiled-load-store
5/7 Test #5: vector_addition-tiled-load-store ...   Passed    0.03 sec
    Start 6: syclAvgPooling
6/7 Test #6: syclAvgPooling .....................   Passed    0.03 sec
    Start 7: clVectorAddition
7/7 Test #7: clVectorAddition ...................   Passed    0.04 sec

100% tests passed, 0 tests failed out of 7

More information can be gathered by passing --verbose to the ctest command.

Providing extra options

The following environment variables are mostly used for testing and trying out options without having to modify the source.

  • CA_EXTRA_COMPILE_OPTS: This option is used to specify additional compile options when building a kernel.
  • CA_EXTRA_LINK_OPTS: This option is used to specify additional link options in the same manner as CA_EXTRA_COMPILE_OPTS.
  • CA_LLVM_OPTIONS: This environment variable allows the injection of LLVM flags only when either NDEBUG is not defined (i.e. Debug and ReleaseAssert build configurations) or when the CA_ENABLE_LLVM_OPTIONS_IN_RELEASE option is set in CMake. See below for example of how this can be used.
  • CA_HOST_NUM_THREADS: Sets the maximum number of threads the host device will create. host may create fewer threads than this value.

Debugging the LLVM compiler

Developers can use a variety of methods to debug the running of LLVM compiler pipelines without having to recompile the oneAPI Construction Kit. The following suggestions involve passing additional options via CA_LLVM_OPTIONS (detailed above).

-print-after-all (and -print-before-all)

This option prints the state of the compiler IR after (/before) every compiler pass. This can be useful for:

  • understanding compiler flow
  • identifying the source of an unknown bug
  • tracing a known bug through the pipeline

Note: Passes print the unit of IR on which they work: module passes print the whole module; function passes print just the function; loops print only the loop. This can occasionally interfere with bug discovery.

-print-after=X (and -print-before=X)

This option prints the state of the compiler IR after (/before) a specific compiler pass. When given a pass name or comma-separated list of pass names, it prints the IR before or after every instance of those passes, on every unit of IR:

> CA_LLVM_OPTIONS=-print-after=early-cse,mem2reg ...

*** IR Dump After EarlyCSEPass on foo ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @foo(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !10
  %mul = mul nsw i32 %0, 5
  %arrayidx1 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx1, align 4, !tbaa !10
  ret void
}
*** IR Dump After EarlyCSEPass on bar ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @bar(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !10
  %mul = mul nsw i32 %0, 5
  %arrayidx2 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx2, align 4, !tbaa !10
  ret void
}
*** IR Dump After PromotePass on foo ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @foo(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) local_unnamed_addr #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #2
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !10
  %mul = mul nsw i32 %0, 5
  %arrayidx1 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx1, align 4, !tbaa !10
  ret void
}
; <... and on>

The two options can be combined, e.g., to better inspect the result of a specific pass:

> CA_LLVM_OPTIONS="-print-before=early-cse -print-after=early-cse" ...

*** IR Dump Before EarlyCSEPass on bar ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @bar(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %call1 = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call1
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !10
  %mul = mul nsw i32 %0, 5
  %arrayidx2 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx2, align 4, !tbaa !10
  ret void
}
*** IR Dump After EarlyCSEPass on bar ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @bar(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !10
  %mul = mul nsw i32 %0, 5
  %arrayidx2 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx2, align 4, !tbaa !10
  ret void
}

This option is useful for visually inspecting the result of a pass, whether for comprehension or to inspect a compiler bug narrowed down to a specific pass.

Note: This uses the same output format as with -print-after-all/-print-before-all as noted above.

Pass names

The name of the pass can typically be found in any of the pass registry files. The main ComputeMux pass registry is found at modules/compiler/source/base/source/base_module_pass_registry.def, but targets may define their own. LLVM also defines its own, found (through access to the LLVM source code) at llvm/lib/Passes/PassRegistry.def.

Since LLVM ComputeMux use the same style of pass registration, both contain lines such as:

MODULE_PASS("always-inline", AlwaysInlinerPass())

MODULE_PASS("add-sched-params", utils::AddSchedulingParametersPass())

FUNCTION_PASS_WITH_PARAMS("early-cse",
                          "EarlyCSEPass",
                           [](bool UseMemorySSA) {
                             return EarlyCSEPass(UseMemorySSA);
                           },
                          parseEarlyCSEPassOptions,
                          "memssa")

The pass name in each is the first token. For example, always-inline.

Pass name conventions

When adding a new pass, you should ensure its name is properly registered in order that it is testable independently with tools such as muxc.

Use meaningful names for the string literal pass name following the conventions already present in the global registry: terse pass names separated that describe actions are most understandable; dashes separate words; lowercase words separated by dashes where appropriate. This makes them easy to read, understand, type, and require no shell quoting, e.g., remove-fences.

-print-changed

This option works like -print-after-all but only when the pass makes a change to the IR.

*** IR Dump After CoroEarlyPass on [module] omitted because no change ***
*** IR Dump After LowerExpectIntrinsicPass on bar omitted because no change ***
*** IR Dump After SimplifyCFGPass on bar omitted because no change ***
*** IR Dump After EarlyCSEPass on bar ***
; Function Attrs: norecurse nounwind
define dso_local spir_kernel void @bar(ptr addrspace(1) align 4 %a, ptr addrspace(1) align 4 %b) #0 {
entry:
  %call = call spir_func i64 @_Z13get_global_idj(i32 0) #3
  %arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a, i64 %call
  %0 = load i32, ptr addrspace(1) %arrayidx, align 4, !tbaa !9
  %mul = mul nsw i32 %0, 5
  %arrayidx2 = getelementptr inbounds i32, ptr addrspace(1) %b, i64 %call
  store i32 %mul, ptr addrspace(1) %arrayidx2, align 4, !tbaa !9
  ret void
}

Values can be passed to this option to control its behaviour:

  • -print-changed=quiet - Only prints changed IR, suppressing all other messages including the starting IR

Note: There are other values to this option that LLVM supports, like diff and cdiff, which print changes in a useful diff-compatible form. These options currently trigger crashes after certain passes used by the ComputeMux compiler so are not recommended for use.

-verify-each

This option invokes LLVM's IR verifier before and after every pass. The default behaviour is to verify the IR at the beginning and end of every compiler pipeline, so may miss temporal verification errors that are masked by later changes.

This option is useful for identifying whether a compiler pass is generating invalid IR.

-debug-pass-manager

This option gives an overview of each compiler pipeline, listing the passes and analyses running at each point.

> CA_LLVM_OPTIONS=-debug-pass-manager

Running pass: ForceFunctionAttrsPass on [module]
Running analysis: InnerAnalysisManagerProxy<llvm::FunctionAnalysisManager, llvm::Module> on [module]
Running pass: compiler::SoftwareDivisionPass on bar (24 instructions)
  Running analysis: PreservedCFGCheckerAnalysis on bar
Running pass: compiler::StripFastMathAttrs on bar (24 instructions)
; <and on>

Values can be passed to this option to control its behaviour:

  • -debug-pass-manager=quiet - Skips printing of analyses 
    Running pass: ForceFunctionAttrsPass on [module]
Running pass: compiler::SoftwareDivisionPass on bar (24 instructions)
Running pass: compiler::StripFastMathAttrs on bar (24 instructions)
; <and on>
  • -debug-pass-manager=verbose - Prints additional information about pass managers and adaptors. 
    Running pass: ForceFunctionAttrsPass on [module]
Running pass: ModuleToFunctionPassAdaptor on [module]
  Running analysis: InnerAnalysisManagerProxy<llvm::FunctionAnalysisManager, llvm::Module> on [module]
  Running pass: compiler::SoftwareDivisionPass on bar (24 instructions)
    Running analysis: PreservedCFGCheckerAnalysis on bar
Running pass: ModuleToFunctionPassAdaptor on [module]
  Running pass: compiler::StripFastMathAttrs on bar (24 instructions)
; <and on>

-time-passes

Prints timing information summaries at the end of each compiler pipeline, with a breakdown of how long each individual pass took. This is useful for understanding compile-time performance issues.

> CA_LLVM_OPTIONS=-time-passes

===-------------------------------------------------------------------------===
                      ... Pass execution timing report ...
===-------------------------------------------------------------------------===
  Total Execution Time: 0.0044 seconds (0.0044 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
   0.0013 ( 28.9%)   0.0000 (  0.0%)   0.0013 ( 28.9%)   0.0013 ( 28.8%)  ModuleInlinerWrapperPass
   0.0011 ( 24.6%)   0.0000 (  0.0%)   0.0011 ( 24.5%)   0.0011 ( 24.5%)  DevirtSCCRepeatedPass
   0.0005 ( 10.5%)   0.0000 (  0.0%)   0.0005 ( 10.5%)   0.0005 ( 10.5%)  SimplifyCFGPass
   0.0004 (  9.1%)   0.0000 (  0.0%)   0.0004 (  9.0%)   0.0004 (  9.0%)  TargetIRAnalysis
   ; <and on>

Debugging passes with the muxc tool

muxc is a tool, similar to opt, which can be used to run compiler pipelines made of the oneAPI Construction Kit utility passes or provided by the target. This is detailed here.

Running with extra debug support

In non-release mode environment variables can be used for debugging. This can also be supported in release mode if the CMake option CA_ENABLE_DEBUG_SUPPORT is set to ON.

On Bash or similar shells environment variables can be set as follows:

export CA_OCL_DEBUG_PRINT_KERNELS=1

On Windows console:

SET CA_OCL_DEBUG_PRINT_KERNELS=1

Extracting Kernels From Tests

It is possible to extract the source of a kernel being compiled into a file while running the the oneAPI Construction Kit compiler. This is, for example, helpful for extracting kernels from failing test cases in a test suite. Setting the CA_OCL_DEBUG_PRINT_KERNELS environment variable to 1 will enable the feature.

The kernels will be printed in unique files named cl_program_ID.cl the next time the compiler is run, where ID is an incremental numerical value padded with zeroes. Note that the filenames are chosen simply to be unique without any consideration of the contents of the file, so it is possible to get the same kernel in different files, if the kernel is compiled multiple times.

Perf Support for Linux CPU kernels

For Linux hosts which support perf hardware events, we can get various metrics by setting the environment variable CA_ENABLE_PERF_INTERFACE=1 and then running the executable with perf. Since the kernel is being JIT'ed, on Linux hosts.

  1. The compiled kernel object will be placed in /tmp/perf-$\{pid\}.o
  2. A map file with details about the kernel entry function required by perf, are placed in /tmp/perf-${pid}.map

It is possible to disassemble the object code in /tmp/perf-${pid}.o using a disassembler. For a list of hardware events that are supported by perf :

perf list

Some useful events that help with performance analysis are :

  1. branch-instructions
  2. branch-misses
  3. cache-misses
  4. cache-references
  5. cpu-cycles
  6. instructions
  7. mem-loads
  8. mem-stores

To record hardware events for perf, for all the above events,

CA_ENABLE_PERF_INTERFACE=1 perf record \
-e branch-instructions:u,branch-misses:u,cache-misses:u,cache-references:u\
,cpu-cycles:u,instructions:u,mem-loads:u,mem-stores:u <executable> <options>

After recording the profile, you can view the statistics using perf report

Note : Be aware that if you run perf report with the -a option to enable profiling on all the CPUs, all processes running on the OS will be profiled and percentage calculations will take all of them into account. This is most likely Not what you want.

Reducing Rebuild Times With ccache

On supported platforms, such a Linux distribution, it is possible to use ccache to reduce rebuilds times.

ccache is a compiler cache. It speeds up recompilation by caching previous compilations and detecting when the same compilation is being done again.

It can be installed on Ubuntu as follows:

sudo apt install ccache

Once installed ccache is not enabled by default, to use it the PATH environment variable must be updated.

export PATH=/usr/lib/ccache:$PATH

Note that to make this change permanent add the command above to your shell's configuration file, for example ~/.bashrc.

The /usr/lib/ccache directory contains a number of symbolic links which alias common names for compilers installed on the system including; cc, c++, gcc, g++, clang and clang++. These all point to the /usr/bin/ccache executable which handles the caching, when compilation is required ccache dispatches to the actual compiler executable.

If you have installed clang from LLVM's apt repositories ccache will not cache compilation because the executables have a version suffix such as clang-9. There are two choices to enable caching:

Using update-alternatives to manage which clang executable /usr/bin/clang targets, you can do this using:

sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-9 600
sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-9 600

Adding symbolic link targeting /usr/bin/ccache called clang-9, in this example lets assume ~/.local/bin is at the beginning of PATH and will be found before /usr/bin/clang.

ln -s /usr/bin/ccache $HOME/.local/bin/clang-9
ln -s /usr/bin/ccache $HOME/.local/bin/clang++-9

By default ccache has a cache size of 5 Gigabytes which can fill up quickly when working with multiple debug build directories, to increase the cache size to 20 Gigabytes:

ccache -M 20G

With ccache installed any existing build directories will need to be deleted because the originals will not be using the ccache symbolic links. New build directories can be configured as normal however please verify that /usr/lib/ccache is found in the PATH before doing so:

echo $PATH

Now everything is set up we can verify ccache is working as expected using the watch command in combination with ccache -s, which provides cache statistics, in another terminal whilst a build is in progress:

watch ccache -s

If in the rare event ccache may result in bad builds, such as in the event of a hash collision in the cache, the cache can be cleared:

ccache -C

Unfortunately it is not possible to cache all the oneAPI Construction Kit build steps such as building bitcode for the builtins module, this is due to ccache not being aware of the compiler flags passed to clang to generate these outputs.

Enhanced GDB Debugging

Pretty Printers

oneAPI Construction Kit makes use of many non-standard C++ types, such as those in cargo, which do not produce helpful output when used with the GDB print command in a debugging session. To aid in such situations GDB is extensible using the Python API, this can be used to register custom pretty printers for C++ types. cargo provides a set of pretty printers for the types it defines, these can be found in modules/cargo/scripts/gdb/prettyprinters.py. To enable them, issue the following command in a GDB session:

(gdb) source modules/cargo/scripts/gdb/prettyprinters.py

Tracer Guards

Limited internal profiling can be achived with tracer guards. If enabled a .trace file is produced which can be viewed inside chrome, by typing chrome://tracing in the address bar space, clicking Load and selecting your trace file.

You must do two things to get a trace. First build with the any of the following flags (or all of them) -DCA_TRACE_CL=1, -DCA_TRACE_CORE=1, and -DCA_TRACE_IMPLEMENTATION=1. The tracer flags can be set manually in tracer.h or built as part of CMake. Each flag will enable a trace for that layer of the oneAPI Construction Kit.

And second set the environment variable CA_TRACE_FILE=/path/to/save/your.trace E.g: export CA_TRACE_FILE=/tmp/ca.trace. Now when your run your application a .trace file should be written to the location specified.

By default on Linux tracer will stream to a temporary fixed size file using an atomic counter, this removes the need for a mutex on the file. Setting the environment variable CA_TRACE_FILE_BUFFER_MB you can override the default buffer size (1GB). It also has a max size of 75GB which represents the largest tested value.

Benchmarking driver performance with Flamegraphs

  1. Ensure that symbol information is retained when building the oneAPI Construction Kit. This can be done by passing the -DCA_ENABLE_DEBUG_BACKTRACE=ON CMake option. See source/cl/CMakeLists.txt:180 for more information. Without this step, the perf report will not contain anything useful.

  2. Build the oneAPI Construction Kit and the benchmark you'll be using to benchmark the driver (for example, a benchmark from PerfCL).

  3. Clone the Flamegraphs repository: https://github.com/brendangregg/FlameGraph

  4. cd to your benchmark, then use the perf tool to execute your benchmark and record some stack samples:

perf record -g --call-graph dwarf ./jacobi1D (if running the jacobi1D benchmark from PerfCL)

Don't forget to ensure the the oneAPI Construction Kit CL driver is being loaded correctly by the ICD, or you use OCL_ICD_FILENAMES to override the CL driver:

export OCL_ICD_FILENAMES=<path-to-install>/lib/libCL.so

  1. Follow the instructions in the FlameGraph repository to generate a nice SVG:

    • perf script > out.perf
    • $HOME/Work/FlameGraph/stackcollapse-perf.pl out.perf > out.folded
    • $HOME/Work/FlameGraph/flamegraph.pl out.folded > framegraph.svg