This is the approach that I take! (Note: I write graphics and rendering code for a living. "Good enough" for me tends to mean quantizing to either identical p

This is the approach that I take! (Note: I write graphics and rendering code for a living. "Good enough" for me tends to mean quantizing to either identical pixels at the display bit depth or at least perceptually identical pixels. Also, I usually do see a measurable performance benefit to -Ofast over -O3 or -O2. YMMV.) Just like cranking the warning levels as high as I can at the beginning of a project, I also like to build and test with -ffast-math (really -Ofast) from the very beginning. Keeping it warning-free and working under -ffast-math as I go is a lot easier than trying to do it all at once later! And much like the warnings, I find that any new code that fails under -ffast-math tends to be a bit suspect. I've found stuff that tends to break under -ffast-math will also frequently break with a different compiler or on a different hardware architecture. So -ffast-math is a nice canary for that.