#2083 chooses the NaN result of the f32 fma family on the bits: the first
NaN source, quieted in IEEE mode, with the addend skipped when the
product is infinity times zero, and 0xffc00000 otherwise. The selection
and the infinity-times-zero test ran for every fma, but a NaN source
always gives a NaN result, so for any other result they return it
unchanged.
FPNanResultFma32 carries the result and the three sources, with the IEEE
mode as a flag. The SPIR-V emitter makes the selection, including the
infinity-times-zero test, in a branch taken only for a NaN result, and
the SRT evaluator computes it exactly. Add, sub and mul keep the inline
selects: with two sources a branch costs more than it saves.
Karan Vora