[HELP] Enabling SIMD / instruction set selection

Hi there, if I compile OIIO without explicitly setting the SIMD architectures I want to use, does SIMD get skipped altogether? What SIMD architectures should I use for Intel + Apple Silicon Macs?

The issue is a help request about SIMD architecture selection during OIIO compilation, but it names no files, tests, or entry points. Start by locating the compilation settings for SIMD architectures; done means the behavior when settings are omitted and recommendations for Intel and Apple Silicon Macs are documented.

Written by the indexing model from the issue text.