From mboxrd@z Thu Jan  1 00:00:00 1970
From: Craig Burley <burley@gnu.org>
To: martin.kahlert@mchp.siemens.de
Cc: egcs@cygnus.com
Subject: Re: x86 double alignment (was egcs-1.1 release schedule)
Date: Mon, 29 Jun 1998 19:43:00 -0000
Message-id: <199806292135.RAA21094@melange.gnu.org>
References: <19980629141934.A18433@keksy.mchp.siemens.de>
X-SW-Source: 1998-06/msg01075.html

>A small dummy question: Is it possible without big efford, 
>to only align automatic (local) double vars 
>and leave all function parameters untouched? So no ABI gets violatet.
>Most time critical calculations aren't performed on stack doubles,
>i would imagine.

I think that's what we've been concensing on over the past week
already -- 1) get the outgoing stack pointer aligned, so the
callee gets an aligned stack frame of the caller had an aligned
incoming %esp; 2) get double vars aligned within the stack frame;
3) don't do anything different with double vars passed to a
called procedure, since otherwise we'd seriously break the ABI;
4) *maybe* use aligned, frame-based locations for *spills* of
incoming double var args (so instead of spilling by not writing
and just re-reading the original var from the arglist, spill
by writing to an aligned stack temp slot and reading from that;
which costs an extra write, but for lots of reads, gains from
having those reads aligned).

        tq vm, (burley)