From: Samuel Rydh <samuel@ibrium.se>
To: Franz Sirl <Franz.Sirl-ppc@lauterbach.com>
Cc: linuxppc-dev@lists.linuxppc.org
Subject: Re: asm inline
Date: Mon, 2 Dec 2002 18:00:17 +0100 [thread overview]
Message-ID: <20021202170017.GA8469@ibrium.se> (raw)
In-Reply-To: <5.2.0.9.2.20021202155713.01d9b7e8@mail.lauterbach.com>
On Mon, Dec 02, 2002 at 04:12:27PM +0100, Franz Sirl wrote:
> >The compiler does the right thing if -fno-strict-aliasing is used or
> >if 'int b' is replaced by 'ulong b'.
>
> Well, the compiler was right before and as Andreas said, you are wrong. In
> C *(ulong*)&B and *&B are different unrelated objects and the compiler
> optimizes accordingly.
Indeed. A quick check of the ISO C99 standard revealed that the compiler is
allowed to distinguish between int and long even though they share the
same representation on a particular arch.
> Besides the fact that it's almost always right in low-level inline assembly
> to use __asm__ __volatile__ (because without the __volatile__ the __asm__
> maybe hoisted out of loops if the compiler thinks it's a loop invariant),
...which is desirable in this case. The st_le32 inline is just an efficient
way to flip the endian and is not supposted to have any undeclared
side effects (like touching hardware).
/Samuel
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2002-12-02 17:00 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-29 16:08 asm inline Samuel Rydh
2002-11-29 16:21 ` Gabriel Paubert
2002-11-29 17:49 ` Samuel Rydh
2002-12-02 11:17 ` Franz Sirl
2002-12-02 13:11 ` Samuel Rydh
2002-12-02 13:35 ` Andreas Schwab
2002-12-02 14:14 ` Kevin B. Hendricks
2002-12-02 14:29 ` Andreas Schwab
2002-12-02 14:37 ` Kevin B. Hendricks
2002-12-02 14:51 ` Franz Sirl
2002-12-02 15:08 ` Kevin B. Hendricks
2002-12-02 15:11 ` Kevin B. Hendricks
2002-12-02 15:35 ` Franz Sirl
2002-12-02 15:45 ` Kevin B. Hendricks
2002-12-02 15:12 ` Franz Sirl
2002-12-02 17:00 ` Samuel Rydh [this message]
2002-12-02 17:53 ` Gabriel Paubert
2002-12-02 19:17 ` Samuel Rydh
2002-11-29 16:30 ` Benjamin Herrenschmidt
2002-12-02 14:29 ` Gabriel Paubert
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