Re: RFC: Extend x86-64 psABI for 256bit AVX register

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Jun 10, 2008 at 04:50:14PM +0200, Jan Hubicka wrote:
>  1) make __m256 passed on stack on variadic functions and in registers
>  otherwse. Then we don't need to worry about varargs changes at all.
>  This will break unprototyped calls.
>  2) extend rax to pass info about if __m256 registers are present and
>  upper half needs to be saved.
>  This will break passing __m256 arguments to functions with prologues
>  compiled with legacy compiler that will do wild jump.  All other cases
>  should work
>  3) Save upper halves whenever we want to save SSE registers.  This will
>  break calling variadic functions compiled with __m256 support in.
> 
> I guess either 1) or 2) is fine for me, as I told earlier, I am not big
> fan of 3).  I guess 1) is easier and probably make more sense?

I vote for 1), though I think it should be passed on stack only for ...
args.  E.g. for
void foo (__m256 x, ...);
void bar (__m256 x, __m256 y, __m256 z)
{
  foo (x, y, z);
}
the first argument would be passed in %ymm0, while the unnamed arguments
y and z would be pushed to stack.

	Jakub