IEEE compliance doesn't guarantee determinism across different GPUs
No, IEEE compliance does in fact guarantee "determinism" across different GPUs.
No. It does not.
You need a guarantee the generated ISA performs all calculations in the exact same order, which you don't get with IEEE conformance, not even if you use the same HLSL compiler. IEEE also doesn't guarantee the intermediate precision in which calculations are made.
As you can see, I was talking about graphics, not simulation, where e.g. one ulp of color difference "most likely" will not matter.