Codeplay to present at HiPEAC Conference in Haifa

07 November 2013

Codeplay's Paul Keir is delighted to have the opportunity to present at this year's HiPEAC Compiler, Architecture and Tools Conference in Haifa, Israel. The talk is entitled "Fusing GPU kernels within a novel single-source C++ API". The work has been undertaken by Codeplay and TU Berlin's AES group as part of the EU FP7 project: LPGPU. The abstract follows:

Fusing GPU kernels within a novel single-source C++ API

The prospect of GPU kernel fusion is often described in research papers as a standalone command-line tool. Such a tool adopts a usage pattern wherein a user isolates, or annotates, an ordered set of kernels. Given such OpenCL C kernels as input, the tool would output a single kernel, which performs similar calculations, hence minimising costly runtime intermediate load and store operations. Such a mode of operation is, however, a departure from normality for many developers, and is mainly of academic interest.

Automatic compiler-based kernel fusion could provide a vast improvement to the end-user's development experience. The OpenCL Host API, however, does not provide a means to specify opportunities for kernel fusion to the compiler. Ongoing and rapidly maturing compiler and API research by Codeplay aims to provide a higher-level, single-source, industry-focused C++-based interface to OpenCL. Opportunities for kernel fusion have now also been investigated here; utilising features from C++11 including lambda functions; variadic templates; and lazy evaluation using std::bind expressions.

While pixel-to-pixel transformations are interesting in this context, insomuch as they demonstrate the expressivity of this new single-source C++ API, we also consider fusing transformations which utilize synchronization within workgroups. Hence convolutions, utilising halos; and the use of the GPU's local shared memory are also explored.

A perennial problem has therefore been restructured to accommodate a modern C++-based expression of kernel fusion. Kernel fusion thus becomes an integrated component of an extended C++ compiler and API.

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Scott Straughan

UX and Toolkit Engineer