Characterizing Performance Impacts of Subnormal Numbers on Vector Instructions and Transcendental Functions

We investigated the performance impact of IEEE-754 double-precision floating-point subnormal numbers, focusing on vector arithmetic and transcendental functions across Intel, AMD, and HiSilicon CPUs. We developed a benchmark tool, SNBench, and uncovered that subnormal numbers can extend instruction latency and reciprocal throughput by up to 162 cycles on Intel, 13 cycles on AMD, and 2 cycles on HiSilicon processors. The impact is more pronounced in transcendental functions, with performance losses reaching up to 562 cycles on Intel, 404 cycles on AMD, and 62 cycles on HiSilicon CPUs.