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From: "dmalcolm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug analyzer/102692] -Wanalyzer-null-dereference false alarm with (!p || q || !p->next) Date: Fri, 11 Feb 2022 17:40:44 +0000 [thread overview] Message-ID: <bug-102692-4-OoEwiOK6ia@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-102692-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102692 --- Comment #4 from David Malcolm <dmalcolm at gcc dot gnu.org> --- I've been investigating the false positive from -Wanalyzer-use-of-uninitialized-value. It only happens when optimization is turned on, but happens within the FE, before gimplification. Specifically, c_parser_condition parses this condition: ((A OR-IF B) OR-IF C) and calls c_fully_fold on the condition. Within c_fully_fold, fold_truth_andor is called, which bails when optimization is off, but if any optimization is turned on converts the ((A OR-IF B) OR-IF C) into: ((A OR B) OR_IF C) and at gimplification time the inner OR becomes BIT_IOR_EXPR (in gimplify_expr), giving this for the inner condition: tmp = A | B if (tmp) thus effectively synthesizing a redundant access of B when optimization is turned on.
next prev parent reply other threads:[~2022-02-11 17:40 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-10-11 21:47 [Bug analyzer/102692] New: " eggert at cs dot ucla.edu 2021-10-11 22:21 ` [Bug analyzer/102692] " eggert at cs dot ucla.edu 2022-01-07 22:46 ` dmalcolm at gcc dot gnu.org 2022-01-11 14:17 ` cvs-commit at gcc dot gnu.org 2022-02-11 17:40 ` dmalcolm at gcc dot gnu.org [this message] 2022-02-15 21:34 ` cvs-commit at gcc dot gnu.org 2022-02-15 21:39 ` dmalcolm at gcc dot gnu.org
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