aten/src/ATen/native/quantized/cpu/kernels/README.md
The files in this directory are compiled multiple times for different CPU vector instruction sets (e.g. AVX, AVX2). The purpose of putting code in this directory is to make sure we can generate the optimal code for a given processor's vector capabilities. Much of this is done via preprocessor guards in vec256_qint.h.
The considerations for code written in this directory include: