[Bug analyzer/104270] New: -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[Bug analyzer/104270] New: -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104270

            Bug ID: 104270
           Summary: -Wanalyzer-use-of-uninitialized-value is incorrectly
                    suppressed by -ftrivial-auto-var-init=
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

As of GCC 12, the analyzer ought to complain about uses of uninitialized memory
via
  -Wanalyzer-use-of-uninitialized-value 
but fails to do so for trivial cases of locals when -ftrivial-auto-var-init= is
used with "pattern" or "zero".

The docs for -ftrivial-auto-var-init say:

> GCC still considers an automatic variable that doesn't have an explicit
> initializer as uninitialized, @option{-Wuninitialized} will still report
> warning messages on such automatic variables.

which implies that -ftrivial-auto-var-init is intended for mitigation, and that
the analyzer ought to still warn on such cases.

At the gimple level we have e.g.:

  i_1 = .DEFERRED_INIT (4, 1, &"i"[0]);

which the analyzer doesn't yet have any special knowledge about, and thus
treats the result as a normal value, suppressing the warning.

[Bug analyzer/104270] -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104270

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-01-28
           Keywords|                            |diagnostic

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. I suspect it should be easy to treat DEFERRED_INIT as similar to ssa
names that are (D).

[Bug analyzer/104270] -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104270

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:9b4eee5fd158c4ee75d1f1000debbf5082fb9b56

commit r12-6997-g9b4eee5fd158c4ee75d1f1000debbf5082fb9b56
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Fri Jan 28 11:02:09 2022 -0500

    analyzer: stop -ftrivial-auto-var-init from suppressing uninit warnings
[PR104270]

    GCC 12 has gained two features for dealing with uninitialized variables:

    (a) a new -Wanalyzer-use-of-uninitialized-value warning within -fanalyzer
    for interprocedural path-sensitive detection of ununit uses, and

    (b) a new -ftrivial-auto-var-init option for mitigating some uses of
    uninit variables

    It turns out that using (b) was thwarting (a), as it led to -fanalyzer
    seeing calls to IFN_DEFERRED_INIT, which -fanalyzer wasn't
    special-casing, thus treating it as initializing the variables in
    question, and thus silencing -Wanalyzer-use-of-uninitialized-value on
    them.

    invoke.texi says:

    "GCC still considers an automatic variable that doesn't have an explicit
    initializer as uninitialized, @option{-Wuninitialized} will still report
    warning messages on such automatic variables."

    and thus -Wanalyzer-use-of-uninitialized-value ought to as well.

    This patch adds special-case handling to -fanalyzer for
    IFN_DEFERRED_INIT,  so that -fanalyzer will warn on uninit uses of
    variables that are mitigated by -ftrivial-auto-var-init.

    gcc/analyzer/ChangeLog:
            PR analyzer/104270
            * region-model.cc (region_model::on_call_pre): Handle
            IFN_DEFERRED_INIT.

    gcc/testsuite/ChangeLog:
            PR analyzer/104270
            * gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c: New
            test.
            * gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c:
            New test.
            * gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c: New test.

    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

[Bug analyzer/104270] -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104270

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Should be fixed by the above commit.

[Bug analyzer/104270] -Wanalyzer-use-of-uninitialized-value is incorrectly suppressed by -ftrivial-auto-var-init=

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104270

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:fb45d8e692d41d0d5d0fea56791d5dca448009c5

commit r12-7007-gfb45d8e692d41d0d5d0fea56791d5dca448009c5
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Feb 2 16:45:29 2022 -0500

    docs: mention analyzer interaction with -ftrivial-auto-var-init [PR104270]

    gcc/ChangeLog:
            PR analyzer/104270
            * doc/invoke.texi (-ftrivial-auto-var-init=): Add reference to
            -Wanalyzer-use-of-uninitialized-value to paragraph documenting that
            -ftrivial-auto-var-init= doesn't suppress warnings.

    Signed-off-by: David Malcolm <dmalcolm@redhat.com>