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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/108704] Many -Wanalyzer-use-of-uninitialized-value
 false positives seen in qemu's softfloat.c
Date: Wed, 29 Mar 2023 18:19:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108704

--- 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:5da2126c4df8d83c2b2f9de7bb393ab4f5832840

commit r12-9364-g5da2126c4df8d83c2b2f9de7bb393ab4f5832840
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Wed Mar 29 14:16:48 2023 -0400

    analyzer: fix overzealous state purging with on-stack structs [PR108704]

    PR analyzer/108704 reports many false positives seen from
    -Wanalyzer-use-of-uninitialized-value on qemu's softfloat.c on code like
    the following:

       struct st s;
       s =3D foo ();
       s =3D bar (s); // bogusly reports that s is uninitialized here

    where e.g. "struct st" is "floatx80" in the qemu examples.

    The root cause is overzealous purging of on-stack structs in the code I
    added in r12-7718-gfaacafd2306ad7, where at:

            s =3D bar (s);

    state_purge_per_decl::process_point_backwards "sees" the assignment to =
's'
    and stops processing, effectively treating 's' as unneeded before this
    stmt, not noticing the use of 's' in the argument.

    Fixed thusly.

    The patch greatly reduces the number of
    -Wanalyzer-use-of-uninitialized-value warnings from my integration test=
s:
      ImageMagick-7.1.0-57:  10 ->  6   (-4)
                  qemu-7.2: 858 -> 87 (-771)
             haproxy-2.7.1:   1 ->  0   (-1)
    All of the above that I've examined appear to be false positives.

    Cherrypicked from r13-5745-g77bb54b1b07add.

    gcc/analyzer/ChangeLog:
            PR analyzer/108704
            * state-purge.cc (state_purge_per_decl::process_point_backwards=
):
            Don't stop processing the decl if it's fully overwritten by
            this stmt if it's also used by this stmt.

    gcc/testsuite/ChangeLog:
            PR analyzer/108704
            * gcc.dg/analyzer/uninit-7.c: New test.
            * gcc.dg/analyzer/uninit-pr108704.c: New test.

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