A Cross-platform Evaluation of Graphics Shader Compiler Optimization

For real-time graphics applications such as games and virtual reality, performance is crucial to provide a smooth user experience. Central to this is the performance of shader programs which render images on the GPU. The rise of low-level graphics APIs such as Vulkan means compilation tools play an increasingly important role in the graphics ecosystem. However, despite the importance of graphics, there is little published work on the impact of compiler optimization. This paper explores common features of graphics shaders, and examines the impact and applicability of common optimizations such as loop unrolling, and arithmetic reassociation. Combinations of optimizations are evaluated via exhaustive search across a wide set of shaders from the GFXBench 4.0 benchmark suite. Their impact is assessed across three desktop and two mobile GPUs from different vendors. We show that compiler optimization can have significant positive and negative impacts which vary across optimisations, benchmarks and platforms.