Inherent code performance advantages of D over C?

[Simen Kjærås]

On 07.12.2013 08:38, Maxim Fomin wrote:
> On Friday, 6 December 2013 at 23:30:45 UTC, Walter Bright wrote:
>> On 12/6/2013 3:06 PM, Maxim Fomin wrote:
>>> and what about holes in immutable, pure and rest type system?
>>
>> If there are bugs in the type system, then that optimization breaks.
>
> Bad news: there are many bugs in type system.
>
>>
>>> C doesn't have virtual functions.
>>
>> Right, but you can (and people do) fake virtual functions with tables
>> of function pointers. No, C doesn't devirtualize those.
>>
>
> Neither does D.
>
>>> By the way, does D devirtualize them?
>>
>> It does for classes/methods marked 'final'
>
> this is essentially telling nothing, because these functions are not
> virtual. In your speaking, C 'devirtualizes' all direct calling.

They're both virtual and not (sorta). Consider this case:

class A {
     int foo() { return 3; }
}

class B : A {
     final int foo() { return 4; }
}

int bar(A a) {
     return a.foo();
}

void baz(B b) {
     int n = bar(b);
}

If the compiler does not inline the call to bar in baz, a virtual call 
is performed. If it does inline it, then it knows that the function 
called will always be B.foo, even if the received value may be a 
subclass of B.

-- 
   Simen