fix Issue 20567 returning the result of a constructor should be NRVO (#20568)

compiler/test/runnable/nrvo.d

@@ -22,9 +22,35 @@ void test1()
     assert(&r == s1ptr);
 }
 
+/***************************************************/
+// https://github.com/dlang/dmd/issues/20567
+
+struct S2
+{
+    int x;
+    this(ref S2 s) { x = s.x; }
+}
+
+S2 returnRval(ref S2 arg1, ref S2 arg2, int i)
+{
+    return i ? arg1 : arg2;
+}
+
+void test2()
+{
+    S2 s1, s2;
+    s1.x = 3;
+    s2.x = 4;
+    S2 s = returnRval(s1, s2, 0);
+    assert(s.x == 4);
+    s = returnRval(s1, s2, 1);
+    assert(s.x == 3);
+}
+
 /***************************************************/
 
 void main()
 {
     test1();
+    test2();
 }