https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127369
Bug ID: 127369
Summary: std::isfinite/std::isinf do not work reliably
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gero.peterhoff at gmx dot net
Target Milestone: ---
With -O1/2/3/s/z, std::isfinite/std::isinf do not work in an inline context. It
appears that the functions are “optimized away” in that case. However, they
seem to work with noinline or constexpr values. The problem always occurs (not
just with U64->FP16 as in the example), e.g., U128 -> FP32.
This means that many math functions do not work correctly --> showstopper.
Other functions may also be affected.
template <std::floating_point Float>
__attribute__ ((__noinline__)) constexpr bool is_finite(const Float x)
noexcept { return std::isfinite(x); }
template <std::floating_point Float>
__attribute__ ((__noinline__)) constexpr bool is_inf(const Float x)
noexcept { return std::isinf(x); }
int main(const int argc, const char*const*const args)
{
if (argc > 0)
{
using F = std::float16_t;
using U = std::uint64_t;
using I = std::int64_t;
I i = std::atoll(args[1]);
F f = F(U(i)); // inf
std::cout << f << "\n";
std::cout << "finite\t" << std::isfinite(f) << "\t" <<
is_finite(f) << "\n";
std::cout << "inf\t" << std::isinf(f) << "\t" << is_inf(f) <<
"\n";
}
return 0;
}
Compile with -O3 and run with -1:
inf
finite true false
inf false true
