Interface vs pure abstract class - speed.

[D-Ratiseur]

On Sunday, 12 May 2013 at 18:45:29 UTC, Maxim Fomin wrote:
> On Sunday, 12 May 2013 at 18:21:14 UTC, SundayMorningRunner 
> wrote:
>> On Sunday, 12 May 2013 at 18:14:51 UTC, Maxim Fomin wrote:
>>> On Sunday, 12 May 2013 at 17:31:22 UTC, SundayMorningRunner 
>>> wrote:
>>>> Hello, let's say I have the choice between using an abstract 
>>>> class or an interface to declare a "plan", a "template" for 
>>>> the descendants.
>>>> From the dmd compiler point of view, should I use the 
>>>> abstract class version (so I guess that for each method 
>>>> call, there will be a few MOV, in order to extract the 
>>>> relative address from the vmt before a CALL) or the 
>>>> interface version (are the CALL directly performed in this 
>>>> case). Are interface faster ? (to get the address used by 
>>>> the CALL).
>>>>
>>>> Thx.
>>>
>>> I doubt that looking from buggy compiler POV is a good idea. 
>>> Anyway you can take code and look into assembly.
>> Which is exactly what you could have done before answering ;)
>
> This is exactly what I *have done* before answering to get 
> correct answer for me. I see no reasons to ask such questions 
> if you can do the test yourself.
>
> interface I
> {
>    void foo();
> }
>
> class A : I { void foo(){}}
>
> abstract class B { void foo() {} }
> class C : B {}
>
> void bar(C c, I i)
> {
>    c.foo();
>    i.foo();
> }
>
> void main()
> {
>    A a = new A;
>    a.foo();
>    C c = new C;
>    c.foo();
>    bar(c, a);
> }
> disas _Dmain
> Dump of assembler code for function _Dmain:
>    0x0000000000419cd8 <+0>:	push   %rbp
>    0x0000000000419cd9 <+1>:	mov    %rsp,%rbp
>    0x0000000000419cdc <+4>:	sub    $0x10,%rsp
>    0x0000000000419ce0 <+8>:	movabs $0x639210,%rdi
>    0x0000000000419cea <+18>:	callq  0x41becc <_d_newclass>
>    0x0000000000419cef <+23>:	mov    %rax,-0x10(%rbp)
>    0x0000000000419cf3 <+27>:	mov    %rax,%rdi
>    0x0000000000419cf6 <+30>:	mov    (%rax),%rcx
>    0x0000000000419cf9 <+33>:	rex.W callq *0x28(%rcx)
>    0x0000000000419cfd <+37>:	movabs $0x639380,%rdi
>    0x0000000000419d07 <+47>:	callq  0x41becc <_d_newclass>
>    0x0000000000419d0c <+52>:	mov    %rax,-0x8(%rbp)
>    0x0000000000419d10 <+56>:	mov    %rax,%rdi
>    0x0000000000419d13 <+59>:	mov    (%rax),%rdx
>    0x0000000000419d16 <+62>:	rex.W callq *0x28(%rdx)
>    0x0000000000419d1a <+66>:	mov    -0x8(%rbp),%rsi
>    0x0000000000419d1e <+70>:	cmpq   $0x0,-0x10(%rbp)
>    0x0000000000419d23 <+75>:	je     0x419d2f <_Dmain+87>
>    0x0000000000419d25 <+77>:	mov    -0x10(%rbp),%rax
>    0x0000000000419d29 <+81>:	lea    0x10(%rax),%rdi
>    0x0000000000419d2d <+85>:	jmp    0x419d32 <_Dmain+90>
>    0x0000000000419d2f <+87>:	xor    %rdi,%rdi
> ---Type <return> to continue, or q <return> to quit---
>    0x0000000000419d32 <+90>:	callq  0x419cb0 
> <_D4main3barFC4main1CC4main1IZv>
>    0x0000000000419d37 <+95>:	xor    %eax,%eax
>    0x0000000000419d39 <+97>:	leaveq
>    0x0000000000419d3a <+98>:	retq
> End of assembler dump.
> disas _D4main3barFC4main1CC4main1IZv
> Dump of assembler code for function 
> _D4main3barFC4main1CC4main1IZv:
>    0x0000000000419cb0 <+0>:	push   %rbp
>    0x0000000000419cb1 <+1>:	mov    %rsp,%rbp
>    0x0000000000419cb4 <+4>:	sub    $0x10,%rsp
>    0x0000000000419cb8 <+8>:	mov    %rdi,-0x10(%rbp)
>    0x0000000000419cbc <+12>:	mov    %rsi,%rdi
>    0x0000000000419cbf <+15>:	mov    (%rsi),%rax
>    0x0000000000419cc2 <+18>:	rex.W callq *0x28(%rax)
>    0x0000000000419cc6 <+22>:	mov    -0x10(%rbp),%rdi
>    0x0000000000419cca <+26>:	mov    (%rdi),%rcx
>    0x0000000000419ccd <+29>:	rex.W callq *0x8(%rcx)
>    0x0000000000419cd1 <+33>:	leaveq
>    0x0000000000419cd2 <+34>:	retq
> End of assembler dump.

so take a tip: go on home.
so take a tip: you'll never beat the IRA.