Most efficient standard-compliant way of reinterpreting int as float

Assume I have guarantees that float is IEEE 754 binary32. Given a bit pattern that corresponds to a valid float, stored in std::uint32_t, how does one reinterpret it as a float in a most efficient standard compliant way?

float reinterpret_as_float(std::uint32_t ui) {
   return /* apply sorcery to ui */;
}

I've got a few ways that I know/suspect/assume have some issues:

1. Via reinterpret_cast,

   float reinterpret_as_float(std::uint32_t ui) {
       return reinterpret_cast<float&>(ui);
   }
   

   or equivalently

   float reinterpret_as_float(std::uint32_t ui) {
       return *reinterpret_cast<float*>(&ui);
   }
   

   which suffers from aliasing issues.

2. Via union,

   float reinterpret_as_float(std::uint32_t ui) {
       union {
           std::uint32_t ui;
           float f;
       } u = {ui};
       return u.f;
   }
   

   which is not actually legal, as it is only allowed to read from most recently written to member. Yet, it seems some compilers (gcc) allow this.

3. Via std::memcpy,

   float reinterpret_as_float(std::uint32_t ui) {
       float f;
       std::memcpy(&f, &ui, 4);
       return f;
   }
   

   which AFAIK is legal, but a function call to copy single word seems wasteful, though it might get optimized away.

4. Via reinterpret_casting to char* and copying,

   float reinterpret_as_float(std::uint32_t ui) {
       char* uip = reinterpret_cast<char*>(&ui);
       float f;
       char* fp = reinterpret_cast<char*>(&f);
       for (int i = 0; i < 4; ++i) {
           fp[i] = uip[i];
       }
       return f;
   }
   

   which AFAIK is also legal, as char pointers are exempt from aliasing issues and manual byte copying loop saves a possible function call. The loop will most definitely be unrolled, yet 4 possibly separate one-byte loads/stores are worrisome, I have no idea whether this is optimizable to single four byte load/store.

The 4 is the best I've been able to come up with.

Am I correct so far? Is there a better way to do this, particulary one that will guarantee single load/store?