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From: "joseph at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/67999] Wrong optimization of pointer comparisons
Date: Wed, 28 Oct 2015 02:29:00 -0000	[thread overview]
Message-ID: <bug-67999-4-Q8R9hmBIWs@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-67999-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67999

--- Comment #24 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I suppose that while EXACT_DIV_EXPR on the individual halves of a 
subtraction wouldn't be correct, it would also be correct (given any 
constant element size) to do the (right shift, multiply by reciprocal of 
odd part) combination, that works for exact division without needing a 
multiplication high part, on each pointer, because the subtraction would 
cancel out the matching errors from the two pointers not being divisible 
by the size of the type.


  parent reply	other threads:[~2015-10-28  2:29 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-67999-4@http.gcc.gnu.org/bugzilla/>
2015-10-17  8:03 ` glisse at gcc dot gnu.org
2015-10-17  8:14 ` pinskia at gcc dot gnu.org
2015-10-17  8:35 ` schwab@linux-m68k.org
2015-10-17 12:52 ` ch3root at openwall dot com
2015-10-19  2:30 ` danielmicay at gmail dot com
2015-10-19  5:36 ` bugdal at aerifal dot cx
2015-10-19  8:17 ` fw at gcc dot gnu.org
2015-10-19  8:26 ` fw at gcc dot gnu.org
2015-10-19  8:41 ` danielmicay at gmail dot com
2015-10-19  8:47 ` danielmicay at gmail dot com
2015-10-19  9:05 ` fw at gcc dot gnu.org
2015-10-19  9:09 ` fw at gcc dot gnu.org
2015-10-19  9:12 ` danielmicay at gmail dot com
2015-10-19  9:26 ` danielmicay at gmail dot com
2015-10-19  9:55 ` danielmicay at gmail dot com
2015-10-19  9:56 ` rguenth at gcc dot gnu.org
2015-10-19 10:12 ` jakub at gcc dot gnu.org
2015-10-21  2:09 ` ch3root at openwall dot com
2015-10-21  2:18 ` ch3root at openwall dot com
2015-10-21  3:21 ` danielmicay at gmail dot com
2015-10-28  0:12 ` joseph at codesourcery dot com
2015-10-28  0:20 ` bugdal at aerifal dot cx
2015-10-28  2:29 ` joseph at codesourcery dot com [this message]
2015-10-28 18:26 ` ch3root at openwall dot com

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