Dynamic stack alignment for i386

[law@redhat.com]

In message <20020529153023.B4546@redhat.com>, Richard Henderson writes:
 > On Wed, May 29, 2002 at 08:26:50PM +0100, Bernd Schmidt wrote:
 > > I'm pretty sure we need to know the arg pointer's regno before we know
 > > the required alignment, so I'm not sure how feasible this is.
 > 
 > The compiler supports the arg pointer as a pseudo.  Jeff's work on
 > PA64 required this, IIRC.  Thus we needn't reserve _any_ register
 > for this.
Yea.  Actually it tried to support it before PA64 on some other weird
chip and it was mostly correct.

The outgoing argument pointer is put into %r29 by the caller.  The callee
copies it into a new pseudo and that pseudo is used for the callee's argument
pointer.  This is mostly (completely?) handled by generic code in the
compiler.

jef