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Re: Altivec + 16 byte alignment

From: Richard Henderson <rth at redhat dot com>
To: Geoff Keating <geoffk at geoffk dot org>
Cc: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>, gcc at gcc dot gnu dot org
Date: Tue, 11 Feb 2003 16:52:17 -0800
Subject: Re: Altivec + 16 byte alignment
References: <10302111946.AA20111@vlsi1.ultra.nyu.edu> <jmheba4mfs.fsf@desire.geoffk.org>

On Tue, Feb 11, 2003 at 12:00:39PM -0800, Geoff Keating wrote:
> The code is, naturally, machine-dependent.  For rs6000, I believe it's
> not implemented yet.  For x86, it's in ix86_compute_frame_layout, look
> for the variable 'stack_alignment_needed'.

No, the code does not exist in mainline at all.  It was once
written in a Cygnus branch, but it was really sort of ugly,
and never made it out.

STACK_BOUNDARY is an ABI issue; PREFERRED_STACK_BOUNDARY is an
optimization goal.  However, without forcibly aligning the stack
with AND, one cannot assume more than STACK_BOUNDARY, because 
that's the most we can expect from a different compiler (or gcc
with a different set of options).

r~

References:
- Re: Altivec + 16 byte alignment
  - From: Richard Kenner
- Re: Altivec + 16 byte alignment
  - From: Geoff Keating

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