From: "Joseph S. Myers" <joseph@codesourcery.com>
To: Steve Ellcey <sje@cup.hp.com>
Cc: gcc@gcc.gnu.org
Subject: Re: memcpy / Language Lawyer / optimization question
Date: Thu, 09 Dec 2004 20:20:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.61.0412092017440.5206@digraph.polyomino.org.uk> (raw)
In-Reply-To: <200412091932.LAA06762@hpsje.cup.hp.com>
On Thu, 9 Dec 2004, Steve Ellcey wrote:
> My question is about the second memcpy where I cast to (void *). This
> still results in an abort on IA64 because it is still assuming integer
> alignment (and thus changing the code to do an integer assignment). Is
> it legal to do this transformation with the (void *) cast?
The casts in the calls to memcpy are irrelevant: the undefined behavior
occurs before them, at the point where you cast an unaligned pointer to
int *. Casting a pointer to another pointer type for which it doesn't
have the alignment yields undefined behavior. The compiler can assume
that the result of a sequence of pointer casts has the alignment of
whichever type in the sequence of pointer types has the strictest
alignment requirements.
--
Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/
jsm@polyomino.org.uk (personal mail)
joseph@codesourcery.com (CodeSourcery mail)
jsm28@gcc.gnu.org (Bugzilla assignments and CCs)
next prev parent reply other threads:[~2004-12-09 20:20 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-09 19:33 Steve Ellcey
2004-12-09 19:41 ` Joe Buck
2004-12-09 19:52 ` Paul Jarc
2004-12-09 20:11 ` Gabriel Dos Reis
2004-12-09 20:14 ` Joe Buck
2004-12-09 20:20 ` Joseph S. Myers [this message]
2004-12-10 16:51 ` Steve Ellcey
2004-12-09 22:54 Paul Schlie
2004-12-09 23:36 ` Geoffrey Keating
2004-12-09 23:53 ` Joe Buck
2004-12-10 3:18 ` Paul Schlie
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