I also learned from experience that -ffast-math only enables the FTZ/DAZ optimization on the main thread, at least on Linux/X86. I don’t know if its universal or this has changed since I debugged it ~5-6 years ago, but that proved to be a bit hard to get to the bottom of since I immediately suspected the big CPU spike when the volume was set very low was caused by denormals, yet we were using the —ffast-math gcc flag.