proposed syntax change

[Robert Jacques]

On Fri, 07 Aug 2009 15:44:04 -0700, Sergey Gromov <snake.scaly at gmail.com>  
wrote:

> Fri, 07 Aug 2009 13:47:31 -0700, Robert Jacques wrote:
>
>> On Fri, 07 Aug 2009 12:03:43 -0700, Yigal Chripun <yigal100 at gmail.com>
>> wrote:
>>
>>> regarding the div() function above, I was thinking about using D's  
>>> naked
>>> asm feature. From what little I know about this, the compiler doesn't
>>> generate the usual asm code for this sort of function to handle
>>> registers, stack, etc, and you're supposed to do everything yourself in
>>> asm.
>>
>> IIRC naked asm only works for zero-argument and single arguments of size
>> 1,2 or 4 functions, which div is not.
>>
>>> I don't think your comment above about the function call overhead
>>> applies if div is implemented in such a way but I'm no expert and
>>> someone more knowledgeable can shed more light on this. (Don?)
>>
>> If you check the D ABI, one of the arguments must be passed on the  
>> stack,
>> the other in a specific register (EAX).
>> http://www.digitalmars.com/d/2.0/abi.html
>> So the backend can't do things like ECX = EBX / EDX. Instead it has to
>> save/restore whatever's in EAX, ECX and EDX before/after the div call.
>
> Inlined functions become integral part of their outer functions and
> therefore are not obliged to follow ABI. They don't have prologues,
> epilogues, call overhead, etc.

Yes and no. This is quite true for normal D functions, but throwing manual  
asm into the mix does mess up register allocation, etc. Even with naked  
asm, a minimum three registers must be saved.

> Moreover compiler intrinsics are
> functions which compiler recognizes and treats specially, usually by
> replacing them with a single processor instruction.

We weren't discussing implementation with intrinsics, but as with a  
standard library function.