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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
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102692

--- 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 optimizat=
ion
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 =3D A | B
  if (tmp)

thus effectively synthesizing a redundant access of B when optimization is
turned on.=