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From: "chip at pobox dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/56726] i386: MALLOC_ABI_ALIGNMENT is too small (usually)
Date: Mon, 25 Mar 2013 22:36:00 -0000	[thread overview]
Message-ID: <bug-56726-4-Ja8t9M8wMX@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-56726-4@http.gcc.gnu.org/bugzilla/>


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56726

--- Comment #4 from Chip Salzenberg <chip at pobox dot com> 2013-03-25 22:35:57 UTC ---
If I'm reading that correctly, it seems to agree with my patch.

It looks like MALLOC_ABI_ALIGNMENT of POINTER_SIZE*2 is always either correct
or smaller than necessary, but never too large.  If MALLOC_ABI_ALIGNMENT is
smaller than necessary then optimizations may be missed (depending on the
values).  But if it is too large then performance *will* suffer.  It might even
cause exceptions from unaligned accesses, but i386 is very forgiving, so it'll
just be slower for no apparent reason.

Perhaps the glibc version differences in malloc should be advertised with
__attribute__ on the malloc declarations.  Perhaps a new pragma or attribute is
required to do this 100% right.  But in the meantime I like POINTER_SIZE*2.


  parent reply	other threads:[~2013-03-25 22:36 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-25 19:11 [Bug target/56726] New: " chip at pobox dot com
2013-03-25 20:04 ` [Bug target/56726] " hjl.tools at gmail dot com
2013-03-25 21:35 ` chip at pobox dot com
2013-03-25 22:07 ` hjl.tools at gmail dot com
2013-03-25 22:36 ` chip at pobox dot com [this message]
2013-03-26 14:27 ` rguenth at gcc dot gnu.org
2013-03-29  6:05 ` chip at pobox dot com
2013-09-05 20:05 ` chip at pobox dot com
2014-06-12 17:11 ` chip at pobox dot com
2015-04-02 11:36 ` fweimer at redhat dot com
2015-04-02 11:53 ` jakub at gcc dot gnu.org
2015-04-02 21:48 ` chip at pobox dot com
2015-04-06 16:28 ` fweimer at redhat dot com

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