https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121652
--- Comment #6 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Andrew Waterman from comment #5)
> My recollection is that Annex F leaves signaling NaN behavior
> implementation-defined, and so setting the invalid flag on signaling NaN is
> permitted but not required.
It is required by Glibc manual:
-- Macro: int FE_SNANS_ALWAYS_SIGNAL
This macro, defined by TS 18661-1:2014, is defined to ‘1’ in
‘fenv.h’ to indicate that functions and operations with signaling
NaN inputs and floating-point results always raise the invalid
exception and return a quiet NaN, even in cases (such as ‘fmax’,
‘hypot’ and ‘pow’) where a quiet NaN input can produce a non-NaN
result. Because some compiler optimizations may not handle
signaling NaNs correctly, this macro is only defined if compiler
support for signaling NaNs is enabled. That support can be enabled
with the GCC option ‘-fsignaling-nans’.
Thus the RISC-V implementation needs to raise it unless you announce
-fsignaling-nans completely unsupported on RISC-V.
