Evaluating SIMD Compiler-Intrinsics for Database Systems

Abstract

Modern query engines often use SIMD instructions to speed up query performance. As these instructions are heavily CPU-specific, developers must write multiple variants of the same code to support multiple target platforms such as AVX2, AVX512, and ARM NEON. This process leads to logical code duplication, which is cumbersome, hard to test, and hard to benchmark. In this paper, we make the case for writing less platform-specific SIMD code by leveraging the compiler’s own platform-independent SIMD vector abstraction. This allows developers to write a single code variant for all platforms as with a SIMD library, without the library’s redundant layers of abstraction. Clang and GCC implement the platforms’ SIMD intrinsics on top of their own abstraction, so code written in it is optimized for the underlying vector instructions by the compiler. We conduct four database operation microbenchmarks based on code in real systems on x86 and ARM and show that compiler-intrinsic variants achieve the same or even better performance than platform-intrinsics in most cases. In addition, we completely replace the SIMD library in the state-of-the-art query engine Velox with compiler-intrinsics. Our results show that query engines can achieve the same performance with platform-independent code while requiring significantly less SIMD code and fewer variants.