Final necessary for inline optimization?

[IGotD-]

When I'm playing around with different D compilers I get 
different results regarding class method inlining. According most 
information I have seen, you must declare a class method final 
for the compiler to be able inline the method otherwise it will 
be a virtual table call.

Take this simple example.

import std.stdio;
import std.random;

class TestClass
{
     static auto rnd = Random(42);
     int tt = 3;

     void doStuff()
     {
         tt = uniform(0, 15, rnd);
     }
}

void main()
{
     auto c = new TestClass;

     c.doStuff();

     writeln("TestClass is ", c.tt);
}


The random generator is used here so that CTFE doesn't kick in.

DMD certainly doesn't inline unless I use final (on class or 
doStuff) but when I use LDC, LDC seems to be able to figure out 
that the class isn't derived and inlines it regardless (-O option 
required). I see that LDC generates the method doStuff so it 
could also be that LDC knows which specific class it is (and not 
a derived one) in main and can inline for this particular case. 
Which one is it, LDC recognizes TestClass isn't derived or is 
sure that the class (c) isn't derived in particular? Would that 
mean that the vtable entry for doStuff is created regardless? Any 
other information why LDC do better?

I have previously seen a failed attempt to make final default 
(https://forum.dlang.org/thread/lfqoan$5qq$1@digitalmars.com?page=1) but would that be necessary. Could the compiler figure out that a class method is final and manage that optimization by itself?