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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/47679] [4.8/4.9/5 Regression] Strange uninitialized warning after SRA Date: Mon, 16 Feb 2015 23:39:00 -0000 [thread overview] Message-ID: <bug-47679-4-cxgVuwoZ3N@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-47679-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47679 Jeffrey A. Law <law at redhat dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |law at redhat dot com --- Comment #17 from Jeffrey A. Law <law at redhat dot com> --- Couldn't this be seen as a failure to thread jumps? In the rs676361 testcase we have the following relevant blocks after DOM2: ;; basic block 2, loop depth 0 ;; pred: ENTRY aOldItem = getitem (); [return slot optimization] aNewItem_19 = 0; _9 = MEM[(bool *)this_4(D)]; if (_9 != 0) goto <bb 3>; else goto <bb 4>; ;; succ: 3 ;; 4 ;; basic block 3, loop depth 0 ;; pred: 2 aNewItem$8_22 = MEM[(const long unsigned int &)this_4(D) + 8]; aNewItem$8_20 = aNewItem$8_22; aNewItem_21 = 1; ;; succ: 4 ;; basic block 4, loop depth 0 ;; pred: 3 ;; 2 # aNewItem_24 = PHI <1(3), 0(2)> # aNewItem$8_23 = PHI <aNewItem$8_22(3), aNewItem$8_6(D)(2)> _5 = MEM[(bool *)&aOldItem]; _10 = ~_5; _11 = VIEW_CONVERT_EXPR<const bool>(aNewItem_24); _12 = ~_11; if (_10 == _12) goto <bb 5>; else goto <bb 7>; ;; succ: 5 ;; 7 ;; basic block 5, loop depth 0 ;; pred: 4 if (_10 != 0) goto <bb 7>; else goto <bb 6>; ;; succ: 7 ;; 6 ;; basic block 6, loop depth 0 ;; pred: 5 _13 = MEM[(const long unsigned int &)&aOldItem + 8]; aNewItem$8_14 = aNewItem$8_23; iftmp.4_15 = _13 == aNewItem$8_23; _16 = ~iftmp.4_15; _17 = (int) _16; ;; succ: 7 The key here is that we know the value of _12 depending on how we reach block #4. If BB4 then transfers control to block #5 we'll also know the value of _10 which would allow us to thread jumps and I believe simplifies things enough to avoid the false positive, at least on the reduced case. I haven't tried case from Sergey yet. This appears to be caused by a few deficiencies in jump threading. None appear to be major issues though.
next prev parent reply other threads:[~2015-02-16 23:39 UTC|newest] Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-02-10 14:48 [Bug tree-optimization/47679] New: [4.6 " jakub at gcc dot gnu.org 2011-02-10 14:53 ` [Bug tree-optimization/47679] " jakub at gcc dot gnu.org 2011-02-10 16:00 ` jakub at gcc dot gnu.org 2011-02-10 16:19 ` rguenth at gcc dot gnu.org 2011-02-10 16:29 ` jakub at gcc dot gnu.org 2011-02-10 16:29 ` jakub at gcc dot gnu.org 2011-03-03 11:27 ` rguenth at gcc dot gnu.org 2011-03-25 20:09 ` [Bug tree-optimization/47679] [4.6/4.7 " jakub at gcc dot gnu.org 2011-06-27 16:00 ` jakub at gcc dot gnu.org 2011-10-26 17:57 ` jakub at gcc dot gnu.org 2012-03-01 15:16 ` jakub at gcc dot gnu.org 2013-04-12 15:16 ` [Bug tree-optimization/47679] [4.7/4.8/4.9 " jakub at gcc dot gnu.org 2013-08-30 13:04 ` Woebbeking at web dot de 2014-02-16 13:13 ` jackie.rosen at hushmail dot com 2014-06-12 13:44 ` [Bug tree-optimization/47679] [4.7/4.8/4.9/4.10 " rguenth at gcc dot gnu.org 2014-12-19 13:27 ` [Bug tree-optimization/47679] [4.8/4.9/5 " jakub at gcc dot gnu.org 2015-01-12 17:11 ` gafnium@yandex-team.ru 2015-02-16 23:39 ` law at redhat dot com [this message] 2015-04-15 18:52 ` [Bug tree-optimization/47679] [4.8/4.9/5/6 " law at gcc dot gnu.org 2015-04-17 19:24 ` law at gcc dot gnu.org 2015-06-23 8:23 ` rguenth at gcc dot gnu.org 2015-06-26 19:56 ` [Bug tree-optimization/47679] [4.9/5/6 " jakub at gcc dot gnu.org 2015-06-26 20:28 ` jakub at gcc dot gnu.org 2015-09-14 20:11 ` law at gcc dot gnu.org 2015-09-15 17:04 ` law at gcc dot gnu.org 2015-09-16 17:26 ` law at gcc dot gnu.org 2015-09-17 3:01 ` law at gcc dot gnu.org 2015-09-18 15:29 ` law at gcc dot gnu.org 2015-09-18 19:34 ` law at gcc dot gnu.org 2015-09-19 2:57 ` law at gcc dot gnu.org 2015-09-20 6:16 ` law at redhat dot com 2015-09-20 6:40 ` law at gcc dot gnu.org 2015-09-20 6:40 ` [Bug tree-optimization/47679] [4.9/5 " law at redhat dot com
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