sibnick / vc4c

Compiler for the VC4CL OpenCL implementation

VC4C

Compiler for the VC4CL OpenCL-implementation. This compiler supports OpenCL C (via LLVM or SPIRV-LLVM), LLVM-IR and SPIR-V code, depending on the build configuration.

Required software

• A C++11 capable compiler
• CMake in version >= 3.1
• A suitable OpenCL 1.2 compiler. Supported versions are the "original" LLVM/CLang, which can be found in the Raspbian repositories, and Khronos SPIRV-LLVM with the Khronos SPIR-V compiler frontend (only the tools clang and llvm-spirv need to be built).
• The source-code for VC4CLStdLib for the GPU-side standard-library

Build

The following configuration variables can be set in CMake:

• BUILD_TESTING toggles building of test program
• BUILD_DEBUG toggles building debug or release program
• MULTI_THREADED toggles building with multi-threaded support
• VERIFY_OUTPUT toggles the usage of vc4asm to validate the generated machine code
• LLVMIR_FRONTEND toggles building of the LLVM-IR frontend, requires an installed CLang compiler (LLVM or SPIRV-LLVM)
• VC4CL_STDLIB_HEADER_SOURCE sets the headers for the GPU-side VC4CLStdLib, defaults to ../VC4CLStdLib/include/VC4CLStdLib.h
• CROSS_COMPILE toggles whether to cross-compile for the Raspberry Pi, requires the Raspberry Pi cross-compiler to be installed
• CROSS_COMPILER_PATH sets the root path to the Raspberry Pi cross compiler, defaults to /opt/rasperrypi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64 (e.g. for the cross compiler cloned into the directory /opt/raspberrypi/tools/)
• SPIRV_FRONTEND toggles building of the SPIR-V frontend, requires SPIRV-LLVM
• SPIRV_COMPILER_ROOT sets the root-path to binaries of the SPIRV-LLVM compiler, defaults to /opt/SPIRV-LLVM/build/bin/

Known Issues

If the VC4CLStdLib is updated, the LLVM precompiled header (PCH) needs to be rebuilt. For this to happen, simply delete the file include/VC4CLStdLib.h.pch and rebuild the VC4C compiler (or just the vc4cl-stdlib target).

Sometimes, at least on my Raspberry Pi, if a compilation fails, it somehow removes the symbolic /dev/stdout to the current process' standard output, resulting in no program can write to stdout anymore!! To remedy, restart the Pi.