[Bug analyzer/106204] False positive from -Wanalyzer-use-of-uninitialized-value with -ftrivial-auto-var-init=zero

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106204

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by David Malcolm
<dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:09cb9c88ef8e2c0c89ada9cde2caf1a960db7a77

commit r12-8637-g09cb9c88ef8e2c0c89ada9cde2caf1a960db7a77
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Jul 27 17:38:55 2022 -0400

    analyzer: fix uninit false positive with -ftrivial-auto-var-init=
[PR106204]

    (cherry picked from r13-1517-gb33dd7874523af)

    -fanalyzer handles -ftrivial-auto-var-init= by special-casing
    IFN_DEFERRED_INIT to be a no-op, so that e.g.:

      len_2 = .DEFERRED_INIT (4, 2, &"len"[0]);

    is treated as a no-op, so that len_2 is still uninitialized after the
    stmt.

    PR analyzer/106204 reports that -fanalyzer gives false positives from
    -Wanalyzer-use-of-uninitialized-value on locals that have their address
    taken, due to e.g.:

      _1 = .DEFERRED_INIT (4, 2, &"len"[0]);
      len = _1;

    where -fanalyzer leaves _1 uninitialized, and then complains about
    the assignment to "len".

    Fixed thusly by suppressing the warning when assigning from such SSA
    names.

    gcc/analyzer/ChangeLog:
            PR analyzer/106204
            * region-model.cc (within_short_circuited_stmt_p): Move extraction
            of assign_stmt to caller.
            (due_to_ifn_deferred_init_p): New.
            (region_model::check_for_poison): Move extraction of assign_stmt
            from within_short_circuited_stmt_p to here.  Share logic with
            call to due_to_ifn_deferred_init_p.

    gcc/testsuite/ChangeLog:
            PR analyzer/106204
            * gcc.dg/analyzer/torture/uninit-pr106204.c: New test.
            * gcc.dg/analyzer/uninit-pr106204.c: New test.

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