Re: Specifying parameter passing convention and place (register)

[Keith Thompson <kst-u@mib.org>]

"Nick Roberts" <nick.roberts@acm.org> writes:
> What form should a pragma take for specifying the convention and place  
> (register or in memory) for the passing of parameters into and out of  
> subprograms?
[...]
> A different possible approach is the use of representation attributes on  
> subtypes. The GNAT attribute Passed_By_Reference could be used to specify  
> whether a parameter of the subtype is passed by reference or by copy  
> (value). An attribute such as Passing_Place could be a value of an  
> enumeration such as, for example:
> 
>     type Parameter_Passing_Place is
>        ( Default, Stack,
>          AL, AH, DL, DH, CL, CH, BL, BH,
>          AX, DX, CX, BX, SI, DI, BP, SP,
>          EAX, EDX, ECX, EBX, ESI, EDI, EBP, ESP,
>          ST_0, ST_1, ..., ST_7,
>          EDX_EAX, ECX_EBX,
>          ES, FS, GS, ES_EAX, FS_EDX, GS_ECX );
> 
> This way, I can declare, for example:
> 
>     subtype Integer_Passed_In_EAX is Integer;
>     for Integer_Passed_By_EAX'Passing_Place use EAX;
> 
> and then I can declare a function:
> 
>     function Wibble (N: in Integer_Passed_In_EAX)
>        return Integer_Passed_In_EAX;
> 
> in order to specify that the parameter N and the function are both to be  
> passed in the register EAX.
[...]

It seems counterintuitive to associate the parameter passing method
with a subtype rather than with a formal parameter.

What about something like this?

    function Wibble (N: in Integer);
    for Wibble'Parameter_Passing use ( N => EAX );

Adjust names and syntax to taste.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center             <*>  <http://users.sdsc.edu/~kst>
We must do something.  This is something.  Therefore, we must do this.