Inline assembly question

[Basile B.]

On Sunday, 12 November 2017 at 11:01:39 UTC, Dibyendu Majumdar 
wrote:
> Hi,
>
> I have recently started work on building a VM for Lua (actually 
> a derivative of Lua) in X86-64 assembly. I am using the dynasm 
> tool that is part of LuaJIT. I was wondering whether I could 
> also write this in D's inline assembly perhaps, but there is 
> one aspect that I am not sure how to do.
>
> The assembly code uses static allocation of registers, but 
> because of the differences in how registers are used in Win64 
> versus Unix X64 - different registers are assigned depending on 
> the architecture. dynasm makes this easy to do using macros; 
> e.g. below.
>
> |.if X64WIN
> |.define CARG1,		rcx		// x64/WIN64 C call arguments.
> |.define CARG2,		rdx
> |.define CARG3,		r8
> |.define CARG4,		r9
> |.else
> |.define CARG1,		rdi		// x64/POSIX C call arguments.
> |.define CARG2,		rsi
> |.define CARG3,		rdx
> |.define CARG4,		rcx
> |.endif
>
> With above in place, the code can use the mnemonics to refer to 
> the registers rather than the registers themselves. This allows 
> the assembly code to be coded once for both architectures.
>
> How would one do this in D inline assembly?
>
> Thanks and Regards
> Dibyendu

TBH I wonder if this is not worth a enhancement (or even a DIP)
to have in asm blocks a special alias syntax...

{
     asm
     {
         version(...)
         {
            alias First = RDI;
            alias Second = RSI;
            // ...
         }
         else
         {
            alias First = RCX;
            alias Second = RDX;
         }
         mov First, Second;
         call aFunctionWithOneParam; // called with 2nd parent 
param as 1st param
     }
}

since the whole mixin solution make the custom asm unreadable 
just because of this problem.

And Even maybe some special identifiers since extern(...) may 
lead to problems...