[Bug analyzer/102692] -Wanalyzer-null-dereference false alarm with (!p || q || !p->next)

[dmalcolm at gcc dot gnu.org via Gcc-bugs]

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.