GC finalizer optimization.

[Dave]

Argh - I forgot about needing to release synchronization resources or 
zeroing the vptr. regardless of if there is a dtor or not...

Damn.

Dave wrote:
> 
> Comments? Like, how can this break things?
> 
> By changing line 129 of phobos/internal/gc/gc.d from:
> 
> _gc.setFinalizer(p, &new_finalizer);
> 
> to:
> 
> ///_gc.setFinalizer(p, &new_finalizer);
> ///
>     ClassInfo c = ci;
>     do
>     {
>         if (c.destructor)
>         {
>             _gc.setFinalizer(p, &new_finalizer);
>         }
>         c = c.base;
>     } while (c);
> ///
> 
> gives me about 3x performance in allocating class objects w/o a dtor 
> using the following code.
> 
> Before:
> D::~this
> C::~this
> C::~this
> 0.829
> 
> After:
> D::~this
> C::~this
> C::~this
> 0.258
> 
> ;---
> 
> import std.date, std.stdio;
> 
> void main()
> {
>     C c = new C;
>     D d = new D;
>     E e;
>     F f;
> 
>     d_time st = getUTCtime();
>     for(int i = 0; i < 1_000_000; i++)
>     {
>         e = new E;
>         f = new F;
>     }
>     d_time et = getUTCtime();
>     writefln((et - st) / cast(double)TicksPerSecond);
> }
> 
> class C
> {
>     int i;
>     ~this()
>     {
>         printf("C::~this\n");
>     }
> }
> 
> class D : C
> {
>     int i;
>     ~this()
>     {
>         printf("D::~this\n");
>     }
> }
> 
> class E
> {
>     int i;
> }
> 
> class F : E
> {
>     int i;
> }
> 
> Thanks,
> 
> - Dave