https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96804
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- IEEE 754 does not specify the choice of output NaN. None of the C bindings to IEEE 754 specify the choice of output NaN. There are various architecture differences in choice of output NaN (for example, RISC-V always uses a canonical quiet NaN, x87 chooses based on comparing the payloads, SSE chooses based on the operand order to the instruction). Since none of the C bindings specify anything about the choice of output NaN, there is no expectation that particular C syntax constructs map to any particular rules for choice of NaN. And even once you have a choice of NaN from an arithmetic operation, the C bindings leave it implementation-defined whether assignment, function return and other conversions as if by assignment are a convertFormat or copy operation (and convertFormat from a type to itself might change a NaN payload).
