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At least some GCC devs claimed that the standard does not impose any requirements on these macros if a compiler does not claim strict ISO/IEC 6055 (aka IEE 754) conformance (which is still optional, and gcc and clang do not claim it).

Other devs disagree.

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I admit "We don't have to comply with the standard if we don't claim to comply with the standard" is tautologically true.

But it does kind of support the whole "GCC C is not standard C" point.

A C implementation can be fully-compliant without conforming to ISO/IEC 6055, that's optional; question is just whether that optionality extends to fenv.h too. (at least how far I looked, imo it doesn't, and the pragma must exist, and valid fesetround calls (which there may be none of if no FE_* rounding modes are defined) must be represented by FLT_ROUNDS, even if it changes literally no actual float op behavior)

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