Ref-return of dynamic expression emits local variable address return

[controlflow]

Version Used:

master branch @ February 4

Steps to Reproduce:

1. Compile the following code:

class C {
  ref object D(dynamic d) => ref d.Something;
}

2. See the emitted code returning the address of local variables slot:

        ...
        IL_0046: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>::Invoke(!0, !1)
        IL_004b: stloc.0
        IL_004c: ldloca.s 0 // address of 'object' local variable used to capture the result of dynamic expression
        IL_004e: ret        // boom!
    }

Expected Behavior:

The analysis of local address returns should think of references taken with ref expression from dynamic values as locally-allocated. The result of dynamic expression always behaves like "temporary", local expression.

cc @gafter

[VSadov]

cc @jaredpar - for triage.

Another example:

public class C 
{
    public void M() 
    {
        dynamic d = "qq";
        
        foo(ref d.Length);
    }
    
    public static ref dynamic foo(ref dynamic d)
    {
        return ref d;
    }
}

[controlflow]

The same with ref from indexer access:

class C {
  ref object D(dynamic d) => ref d[42];
}