expm1(x) is not folded at the compilation time when x is constant

[k-arrows]

Consider the following C++ example. The function exp(x) is folded, but expm1(x) is not. I still don't have a good idea of how to list these kinds of issues exhaustively.
https://godbolt.org/z/ravEhEEqh

#include <cmath>

double f1() {
  return std::exp(0.)-1.;
}

double f2() {
  return std::expm1(0.);
}