> At best, we can say that if you run the same code generated by the same compiler targeting the same hardware, you'll get identical results. But nothing else is guaranteed.

Basic arithmetic operations of the same size have had guaranteed results for a long time. And the CPU is not going to swap in an FMA instruction, you choose which instructions to use. As of more recently, a bunch of log and exponent and trig operations also have mandatory correct rounding.

> To make matters worse, AMD shipped an incompatible FMA extension that was later removed in Zen 2!

To be clear, this is an annoyance for compiled program compatibility, but it has nothing to do with math compatibility. It's a difference of instruction encoding details.