[Bug d/123422] New: d: RVO/NRVO not done when returning a copy constructor by __rvalue

[ibuclaw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123422

            Bug ID: 123422
           Summary: d: RVO/NRVO not done when returning a copy constructor
                    by __rvalue
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: ibuclaw at gcc dot gnu.org
  Target Milestone: ---

RVO already done when returning a constructor call via a temporary, which in
the front-end AST looks like:

    return S.this((__tmp = {}, &__tmp), args...);

Is rewritten into:

    S.this((*<retval> = {}, <retval>), args...);
    return <retval>;


However in the following test:
```
struct S
{
    S* ptr;
    this(int) { ptr = &this; }
    this(ref inout S) { ptr = &this; }
    this(S) { ptr = &this; }
}

struct V
{
    S s;
    this(int) { s = S(1); }
}

S foo()
{
    return __rvalue(V(1).s); // here
}

void main()
{
    S s = foo();
    assert(&s == s.ptr);
}
```

At the marked location, we instead have:

    return __copytmp = {}, S.this(&__copytmp, V(1).s), __copytmp;

This pattern should also be matched and rewritten in the same way.