From: Andrew Haley <aph@cambridge.redhat.com>
To: Jeff Sturm <jsturm@one-point.com>
Cc: Bryce McKinlay <bryce@waitaki.otago.ac.nz>,
tromey@redhat.com, Dan Nicolaescu <dann@godzilla.ics.uci.edu>,
java@gcc.gnu.org, gcc@gcc.gnu.org
Subject: Re: java aliasing rules
Date: Thu, 04 Apr 2002 12:57:00 -0000 [thread overview]
Message-ID: <15532.46863.497218.134876@cuddles.cambridge.redhat.com> (raw)
In-Reply-To: <Pine.LNX.4.10.10204041316390.14501-100000@mars.deadcafe.org>
Jeff Sturm writes:
> On Sun, 31 Mar 2002, Bryce McKinlay wrote:
> > >>lhz r9, [ps1.f1]
> > >>addi r9,r9,1
> > >>sth r9, [ps1.f1]
> > >>
> > >
> > >Wouldn't accessing r9 immediately after the load cause a pipeline stall?
> > >Assuming an in-order processor? That would be a significant performance
> > >hit.
> >
> > Right, its not optimal scheduling, but there's no way to avoid that and
> > still have the correct behaviour for NullPointers. And as you suggest, a
> > modern processor may be speculativly executing the following loads, so
> > it probibly doesn't matter too much.
If it doesn't annul such speculation on SEGV I don't think it's
correct Java semantics.
> Am I correct in thinking this is only an issue for -fnon-call-exceptions?
Yes.
> It might be useful to turn this "correctness" off with a compiler option,
> as we do with -fno-bounds-check. I habitually check for null in my code,
> and don't do anything useful with a NullPointerException besides aborting.
> I suspect that's true of a great deal of Java code.
I know what you mean, but turning this off is a pretty major departure
from the Java language spec.
Andrew.
next prev parent reply other threads:[~2002-04-04 20:27 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-27 11:43 Dan Nicolaescu
2002-03-27 13:53 ` Tom Tromey
2002-03-27 16:03 ` Dan Nicolaescu
2002-03-27 16:47 ` Tom Tromey
2002-03-27 20:00 ` Dan Nicolaescu
2002-03-27 15:54 ` Bryce McKinlay
2002-03-27 16:45 ` Tom Tromey
2002-03-28 22:02 ` Bryce McKinlay
2002-03-28 22:13 ` Richard Henderson
2002-03-28 22:15 ` Tom Tromey
2002-03-29 15:22 ` Bryce McKinlay
2002-03-29 16:26 ` Richard Henderson
2002-03-30 6:37 ` Jeff Sturm
2002-03-30 13:55 ` Richard Henderson
2002-03-30 15:04 ` Bryce McKinlay
2002-04-04 10:57 ` Jeff Sturm
2002-04-04 12:57 ` Andrew Haley [this message]
2002-04-04 14:20 ` Jeff Sturm
2002-04-04 17:04 ` Bryce McKinlay
2002-04-04 20:39 ` Jeff Sturm
2002-04-05 1:07 ` Bryce McKinlay
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