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Date: Tue, 02 Aug 2005 21:34:00 -0000
From: Joe Buck <Joe.Buck@synopsys.COM>
To: Mike Stump <mrs@apple.com>
Cc: Ian Lance Taylor <ian@airs.com>,
	Andrew Pinski <pinskia@physics.uc.edu>,
	Dave Korn <dave.korn@artimi.com>,
	Paul Koning <pkoning@equallogic.com>, gcc@sources.redhat.com,
	Shaun Jackman <sjackman@gmail.com>
Subject: Re: memcpy to an unaligned address
Message-ID: <20050802213434.GD30893@synopsys.com>
References: <200508022037.j72Kbr4T012558@earth.phy.uc.edu> <m3mzo0jcfm.fsf@gossamer.airs.com> <4AE0FF52-B95D-40D7-B49E-831534AD3CC8@apple.com>
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On Tue, Aug 02, 2005 at 02:29:44PM -0700, Mike Stump wrote:
> On Aug 2, 2005, at 1:45 PM, Ian Lance Taylor wrote:
> >That argument doesn't make sense to me.  memcpy takes a void*
> >argument, which has no presumed alignment.
> 
> The memcpy builtin uses the static type of the actual argument  
> (before conversion to void*), to gain hints about the alignments of  
> the data coming in.  This is so that we can producing nice fast code  
> for 1-16 bytes objects.  This is actually good.  The real problem is  
> formation of the address of the member doesn't produce a pointer to  
> unaligned type, but rather a pointer to aligned type, this is the  
> part that is wrong.  We'd have to add pointers to unaligned data to  
> our type system to fix it.  That should be done, but is a hard/big  
> job, and no one has stepped forward to do it.

So my suggestion to just make pointers to unaligned objects void* would
work in this case, then.