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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/101912] -Wmaybe-uninitialized false alarm in tzdb localtime.c Date: Tue, 30 Nov 2021 15:41:07 +0000 [thread overview] Message-ID: <bug-101912-4-0qUUwyCCVt@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-101912-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101912 Aldy Hernandez <aldyh at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |aldyh at gcc dot gnu.org, | |rguenth at gcc dot gnu.org --- Comment #2 from Aldy Hernandez <aldyh at gcc dot gnu.org> --- ISTM that the warning is correct, given the IL the uninit pass gets. On the 7->3 entry to the loop prevcorr_23 can be undefined, and it is read in BB4 with no guard whatsoever: <bb 7> [local count: 85931698]: <bb 3> [local count: 1034442873]: # prevcorr_23 = PHI <corr_14(8), prevcorr_12(D)(7)> # leapcnt_24 = PHI <leapcnt_15(8), 0(7)> corr_14 = getint (); if (corr_14 <= 0) goto <bb 10>; [3.66%] else goto <bb 4>; [96.34%] <bb 10> [local count: 37860610]: goto <bb 6>; [100.00%] <bb 4> [local count: 996582262]: _1 = corr_14 == 1; _2 = leapcnt_24 != 0; _7 = (unsigned int) prevcorr_23; _5 = _7 + 4294967295; _4 = _5 > 1; _22 = _1 & _2; _18 = _4 & _22; if (_18 != 0) goto <bb 11>; [1.21%] else goto <bb 5>; [98.79%] However, in the original source we shouldn't read from prevcorr if leapcnt == 0, which is the case on entry to the loop: && !(leapcnt == 0 || (prevcorr < corr ? corr == prevcorr + 1 : (corr == prevcorr || corr == prevcorr - 1))))) It looks like we lost the leapcnt gate protecting the prevcorr_23 read. Unless I'm missing some subtle language thinggie, we loose the gate in the ifcombine pass. Before it, the read from prevcorr was protected by: <bb 4> [local count: 996582262]: _1 = corr_14 == 1; _2 = leapcnt_5 != 0; _3 = _1 & _2; if (_3 != 0) goto <bb 5>; [50.00%] else goto <bb 7>; [50.00%] and after ifcombine we have: <bb 4> [local count: 996582262]: _1 = corr_14 == 1; _2 = leapcnt_5 != 0; _3 = _1 & _2; _19 = prevcorr_4 != 1; _16 = _3 & _19; _21 = prevcorr_4 != 2; _18 = _16 & _21; if (_18 != 0) goto <bb 7>; [1.21%] else goto <bb 5>; [98.79%] Unfortunately, adding -fdisable-tree-ifcombine doesn't make the warning go away, but at least the IL by the uninit pass seems correct.
next prev parent reply other threads:[~2021-11-30 15:41 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-14 19:27 [Bug tree-optimization/101912] New: " eggert at cs dot ucla.edu 2021-08-16 17:07 ` [Bug tree-optimization/101912] " msebor at gcc dot gnu.org 2021-11-30 15:41 ` aldyh at gcc dot gnu.org [this message] 2021-11-30 16:02 ` aldyh at gcc dot gnu.org 2021-11-30 16:47 ` eggert at cs dot ucla.edu 2021-12-01 7:49 ` rguenther at suse dot de 2021-12-01 16:22 ` aldyh at gcc dot gnu.org 2022-12-25 0:06 ` pinskia at gcc dot gnu.org 2022-12-27 12:26 ` marxin at gcc dot gnu.org 2023-01-09 10:02 ` rguenth at gcc dot gnu.org 2023-01-09 11:19 ` cvs-commit at gcc dot gnu.org 2023-01-09 11:20 ` rguenth at gcc dot gnu.org 2023-04-12 13:30 ` sjames at gcc dot gnu.org 2023-04-12 13:31 ` sjames at gcc dot gnu.org 2023-04-26 6:55 ` rguenth at gcc dot gnu.org 2023-07-04 9:19 ` rguenth at gcc dot gnu.org 2023-07-04 9:19 ` rguenth at gcc dot gnu.org
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