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From: "schlie at comcast dot net" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/18065] usual arithmetic conversion not applying correctly Date: Sun, 16 Jan 2005 17:39:00 -0000 [thread overview] Message-ID: <20050116173905.31873.qmail@sourceware.org> (raw) In-Reply-To: <20041019202143.18065.schlie@comcast.net> ------- Additional Comments From schlie at comcast dot net 2005-01-16 17:39 ------- Subject: Re: usual arithmetic conversion not applying correctly > From: schlie at comcast dot net <gcc-bugzilla@gcc.gnu.org> > ------- Additional Comments From schlie at comcast dot net 2005-01-16 07:16 > Subject: Re: usual arithmetic conversion not applying correctly > > Wonder if this PR could still be considered a missed optimization, as the > present logic which determines if an / or % expression's operands may be > shortened, misses the case where if the lhs operand is a constant, it may > be verified as not being INT_MIN; as if it's not, then it's impossible for > the operation to overflow, i.e. INT_MIN / -1 => INT_MAX+1, therefore > may be shortened. As noted as being absent in it's comment on shortening: > > /* Although it would be tempting to shorten always here, that loses > on some targets, since the modulo instruction is undefined if the > quotient can't be represented in the computation mode. We shorten > only if unsigned or if dividing by something we know != -1. */ - It would be unfortunate if / and % couldn't be somewhat further optimized prior to 4.0 when their lhs operands are known not to be INT_MIN, as they tend to be typically relatively expensive operations, likely benefiting from shortening more than most. > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18065 > > ------- You are receiving this mail because: ------- > You reported the bug, or are watching the reporter. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18065
next prev parent reply other threads:[~2005-01-16 17:39 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2004-10-19 20:22 [Bug c/18065] New: wrong built-in functions selected schlie at comcast dot net 2004-10-19 20:27 ` [Bug c/18065] " schlie at comcast dot net 2004-10-19 20:39 ` [Bug target/18065] " pinskia at gcc dot gnu dot org 2004-10-19 21:18 ` schlie at comcast dot net 2004-10-19 21:31 ` schlie at comcast dot net 2004-10-19 21:39 ` [Bug target/18065] not using qi version of divmod pinskia at gcc dot gnu dot org 2004-10-19 21:53 ` schlie at comcast dot net 2004-10-19 22:08 ` ericw at evcohs dot com 2004-10-19 22:31 ` schlie at comcast dot net 2004-10-19 23:13 ` ericw at evcohs dot com 2004-10-20 18:34 ` schlie at comcast dot net 2004-10-20 18:50 ` [Bug c/18065] usual arithmetic conversion not applying correctly pinskia at gcc dot gnu dot org 2004-10-20 19:14 ` schlie at comcast dot net 2004-10-20 19:18 ` pinskia at gcc dot gnu dot org 2004-10-20 19:25 ` pinskia at gcc dot gnu dot org 2004-10-20 19:29 ` pinskia at gcc dot gnu dot org 2004-10-20 19:33 ` schlie at comcast dot net 2004-10-20 19:54 ` pinskia at gcc dot gnu dot org 2004-10-20 21:19 ` schlie at comcast dot net 2004-10-20 21:25 ` pinskia at gcc dot gnu dot org 2004-10-20 21:31 ` jsm at polyomino dot org dot uk 2004-10-20 21:46 ` schlie at comcast dot net 2004-10-20 22:27 ` schlie at comcast dot net 2004-10-20 22:31 ` [Bug tree-optimization/18065] " pinskia at gcc dot gnu dot org 2004-10-20 22:42 ` jsm at polyomino dot org dot uk 2004-10-20 23:03 ` jsm at polyomino dot org dot uk 2004-10-20 23:28 ` schlie at comcast dot net 2004-10-21 1:04 ` schlie at comcast dot net 2004-10-21 1:28 ` schlie at comcast dot net 2004-10-21 12:47 ` bangerth at dealii dot org 2004-12-21 20:50 ` schlie at comcast dot net 2005-01-16 1:39 ` pinskia at gcc dot gnu dot org 2005-01-16 7:17 ` schlie at comcast dot net 2005-01-16 17:39 ` schlie at comcast dot net [this message] [not found] <bug-18065-9497@http.gcc.gnu.org/bugzilla/> 2010-09-14 7:06 ` abnikant dot singh at atmel dot com 2010-09-14 7:13 ` abnikant dot singh at atmel dot com [not found] <bug-18065-4@http.gcc.gnu.org/bugzilla/> 2012-05-24 14:03 ` peter777778 at hotmail dot co.uk 2012-05-24 14:04 ` peter777778 at hotmail dot co.uk 2012-05-24 14:05 ` peter777778 at hotmail dot co.uk 2012-05-24 14:23 ` peter777778 at hotmail dot co.uk
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