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From: "manu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/22456] [4.2/4.3/4.4 regression] missing "is used uninitialized" warning Date: Sat, 07 Feb 2009 15:35:00 -0000 [thread overview] Message-ID: <20090207153517.26728.qmail@sourceware.org> (raw) In-Reply-To: <bug-22456-1771@http.gcc.gnu.org/bugzilla/> ------- Comment #17 from manu at gcc dot gnu dot org 2009-02-07 15:35 ------- Without optimization we build the following: foo () { intD.0 iD.1591; # BLOCK 2 # PRED: ENTRY (fallthru) [pr22456.c : 4] goto <bb 4>; # SUCC: 4 (fallthru) # BLOCK 3 # PRED: 4 (true) [pr22456.c : 4] iD.1591_3 = iD.1591_1 + 1; # SUCC: 4 (fallthru) # BLOCK 4 # PRED: 2 (fallthru) 3 (fallthru) # iD.1591_1 = PHI <iD.1591_2(D)(2), iD.1591_3(3)> [pr22456.c : 4] if (iD.1591_1 != 0) goto <bb 3>; else goto <bb 5>; # SUCC: 3 (true) 5 (false) # BLOCK 5 # PRED: 4 (false) [pr22456.c : 5] return; # SUCC: EXIT } Because of the way the loop is represented, we generate a PHI node for the condition instead of a direct use. Since we do not warn about PHI nodes without optimization, then there is no warning. With optimization the loop is completely removed since it doesn't do anything. Hence, there is no warning. I wasn't able to construct a testcase where the loop does anything useful (or the value of "i" is used after the loop) and we do not warn. This doesn't have anything to do with CCP and it is not a duplicate of bug 18501. Closed as INVALID. If anyone comes up with a testcase for this where the loop is not empty, open a new PR and add me to the CC. -- manu at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- BugsThisDependsOn|18501 | Status|NEW |RESOLVED Resolution| |INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22456
next prev parent reply other threads:[~2009-02-07 15:35 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <bug-22456-1771@http.gcc.gnu.org/bugzilla/> 2005-10-12 0:21 ` [Bug middle-end/22456] [4.1 " pinskia at gcc dot gnu dot org 2005-10-31 4:07 ` mmitchel at gcc dot gnu dot org 2006-02-28 20:40 ` [Bug middle-end/22456] [4.1/4.2 " mmitchel at gcc dot gnu dot org 2006-05-25 2:45 ` mmitchel at gcc dot gnu dot org 2007-01-22 17:27 ` [Bug middle-end/22456] [4.1/4.2/4.3 " pinskia at gcc dot gnu dot org 2007-01-28 19:30 ` pinskia at gcc dot gnu dot org 2007-01-28 20:15 ` muntyan at tamu dot edu 2007-02-14 9:34 ` mmitchel at gcc dot gnu dot org 2007-02-19 10:12 ` pinskia at gcc dot gnu dot org 2007-02-19 18:44 ` pinskia at gcc dot gnu dot org 2007-04-11 21:17 ` rguenth at gcc dot gnu dot org 2007-04-11 21:25 ` rguenth at gcc dot gnu dot org 2007-08-15 15:02 ` manu at gcc dot gnu dot org 2007-08-15 15:05 ` manu at gcc dot gnu dot org 2007-08-16 15:22 ` dnovillo at gcc dot gnu dot org 2008-07-04 19:58 ` [Bug middle-end/22456] [4.2/4.3/4.4 " jsm28 at gcc dot gnu dot org 2009-02-07 15:35 ` manu at gcc dot gnu dot org [this message] 2009-02-07 20:35 ` muntyan at tamu dot edu 2009-02-07 20:59 ` manu at gcc dot gnu dot org 2009-02-07 21:33 ` manu at gcc dot gnu dot org 2009-06-17 11:47 ` rguenth at gcc dot gnu dot org 2009-06-17 12:00 ` [Bug middle-end/22456] [4.2/4.3/4.4 regression] (for empty loop) " manu at gcc dot gnu dot org 2009-07-12 21:57 ` reichelt at gcc dot gnu dot org 2009-07-13 6:44 ` manu at gcc dot gnu dot org
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