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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/99671] New: RFE: analyzer could complain about ptr
 derefs that occur before the ptr is checked
Date: Fri, 19 Mar 2021 15:03:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99671

            Bug ID: 99671
           Summary: RFE: analyzer could complain about ptr derefs that
                    occur before the ptr is checked
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

See e.g. bug 80049, where we have code of the form


  expr =3D p->field;
  [...]
  if (p) ...

We could complain that 'p' has already been dereferenced before the check.
This might be implementable using sm-malloc: the "p->field" dereference
transitions "p" to non-null, and we could thus complain at the "if (p)" on
non-null if the transition was due to such a transition (rather than being
known to be non-null) - or perhaps a new state "assumed-non-null"?

PVS Studio complains about this:
  https://www.viva64.com/en/w/v595/
  https://www.viva64.com/en/examples/v595/
using CWE 476:
  https://cwe.mitre.org/data/definitions/476.html=