Re: GCC/powerpc AltiVec expectations.

[Aldy Hernandez <aldyh at redhat dot com>]

> >no.  you'll have to use -mvrsave=yes/no, which affects the entire file,
> >not just one  function.
> 
> How does that work on a file bases?  When would vrsave get set and 
> cleared?

sorry, let me be clear.

you can't use a pragma to enable/disable vrsave generation for a particular
function.  you use -mvrsave=yes to enable vrsave generation for all the
functions in a compilation unit:

	gcc -maltivec -mabi=altivec -mvrsave=yes foo.c

all code in foo.c will maintain vrsave integrity.

bar()
{
	use v50, v51, v52
	hotdog()
}

right before the call to hotdog(), the corresponding bits for v50-v52
will be ORed with the bits already in vrsave.  the caller of bar() will
restore the value of vrsave upon return from bar.

the initial value of vrsave is assumed to be set by the OS.

vrsave generation is on by default in gcc, though since the minority
OS need it, it should be switched to off.

at least that's how i think it works.  i should know, i wrote it.  but i 
should double check though.

is this clearer?

aldy