From: David Edelsohn <dje@watson.ibm.com>
To: "John Yates" <jyates@netezza.com>
Cc: "Yaro Pollak" <yarop@altair-semi.com>, gcc-help@gcc.gnu.org
Subject: Re: Unaligned access to packed structs on ppc405
Date: Sun, 05 Feb 2006 21:02:00 -0000 [thread overview]
Message-ID: <200602052102.k15L2BD28758@makai.watson.ibm.com> (raw)
In-Reply-To: Message from "John Yates" <jyates@netezza.com> of "Sun, 05 Feb 2006 13:35:51 EST." <4D87F853B8020F4888896B1507DC0F09026798@mail2.netezza.com>
>>>>> John Yates writes:
John> Do I read this correctly? Are you truly saying that two structs
John> with identical layout will trigger different code sequences just
John> because one was declared packed?
Yes. Why is that strange? attribute packed assigns the smallest
possible alignment so that the compiler composes the layout of the
structure or bitfield in the more compact form possible. Even if the
layout produced is the same, the smaller alignment is carried around with
the fields and causes the compiler to use more conservative access
operations.
David
next prev parent reply other threads:[~2006-02-05 21:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-05 18:35 John Yates
2006-02-05 21:02 ` David Edelsohn [this message]
2006-02-06 10:18 ` Yaro Pollak
-- strict thread matches above, loose matches on Subject: below --
2006-02-01 12:03 [Re: Unaligned access to packed structs on ppc405] Yaro Pollak
2006-02-04 4:25 ` Unaligned access to packed structs on ppc405 David Edelsohn
2006-01-30 16:18 Matthew Jones
2006-01-30 16:26 ` Yaro Pollak
2006-01-29 17:16 David Edelsohn
2006-01-30 12:03 ` Yaro Pollak
2006-02-02 16:13 ` David Edelsohn
2006-01-29 10:00 Yaro Pollak
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