Re: [f-cpu] calling conventions

["Christophe" <christophe.avoinne@laposte.net>]

> There is another point else which I would enlight : what about the ability to
> use a pair of registers to have 128 bit when 64 bits is default ? especially
> for such opcodes which use or return  a pair of register (Rn,Rn^1) ? not very
> good if the first parameter or return register starts from r1. Worse, what
can
> happen if we use an OPCODE which uses or computes a pair of register
(Rn,Rn^1),
> especially when Rn == R1 ? Rn^1 would be R0, but R0 is hardwired to 0 !

Another proposal :

r0            : zero
r1            : pointer to variable or additional function arguments
(call-clobbered)
r2-r15     : function return values or arguments (call-clobbered)
r16-r31   : temporary registers (call-clobbered)
r32-r47   : local registers (callee-saver)
r48-r63   : global or special registers

that way we could handle pair of registers much smarter
(r2-r3,r3-r4,...,r14,r15).

personally, I'm wondering if it is really necessary to limit function argument
to r15 instead of r31 or r29 (to be sure to have at least a pair of temporary
registers), in so far as we can consider that all function arguments not used
by a function may be used as temporary registers by this function...


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