SIMT to SPMD code translation


At the LHCb detector, bunches of particles collide at a 30 MHz rate, producing a peak data rate of 40 Tbit/s. A data selection is performed over these data, in order to record interesting events from a particle physics standpoint, in a process known as “triggering”. The Allen software framework provides a realization of the first stage of software trigger of the LHCb reconstruction software for GPUs. The entirety of algorithms in Allen is written in CUDA following the SIMT programming model, and are thus restricted to NVIDIA graphics cards hardware. Nevertheless, LHCb software should also support the baseline x86-64 architecture.

The SPMD programming model allows to write vectorized code on CPUs while maintaining a regular coding structure. Under the SPMD model, the programmer writes a program that generally appears to be a regular serial program, though the execution model is actually that a number of program instances execute in parallel on the hardware, in vector units. The Intel SPMD Program Compiler (ISPC) is a realization of a compiler utilizing this model that targets primarily x86 and x86-64 architectures.

The SIMT programming model exposed by CUDA and the SPMD programming model required by ISPC share many commonalities, making the transition from one language to another a nuanced translation exercise. The LLVM Compiler Infrastructure provides a modular compiler and toolchain software infrastructure. LLVM supports compilation of CUDA code, while ISPC is an open source compiler using the LLVM machinery as a backend.

The project aims to provide a basic code translation engine from CUDA into ISPC-understandable code. The student will be provided guidance both through the LLVM infrastructure, and self-contained examples extracted from the Allen codebase. The code translation engine would not only be helpful for the GPU reconstruction under development in LHCb, but for any existing CUDA code with a simple syntax.


Expected results

Working implementation of a basic code translation engine from CUDA into ISPC-understandable code using the LLVM machinery.


Compiler knowledge, CUDA, C


Corresponding Project

Participating Organizations