https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114776

            Bug ID: 114776
           Summary: -Wuse-after-free analysis believes assert() but not
                    g_assert_null()
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alan.coopersmith at oracle dot com
  Target Milestone: ---

Created attachment 57985
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57985&action=edit
Test case

When reviewing the -Wuse-after-free error reported in:
 https://gitlab.freedesktop.org/xorg/lib/libxmu/-/merge_requests/13

in which gcc gives a use-after-free warning for p in:
    p2 = Xmureallocarray(p, 2, ALLOC_LIMIT);
    g_assert_null(p2);
    [...]
    free(p);
even though the realloc failed and returned NULL and did not free p.

I found that the -Wuse-after-free warning went away if I changed
    g_assert_null(p2);
to
    assert(p2 == NULL);

so it appears something in the way g_assert_null from glib is defined
does not convince gcc that p2 must be NULL the way the simple system
assert does.

I've made a cut down test case, and can reproduce the false alarm with

gcc `pkg-config --cflags glib-2.0` -Wall -O2 -c realloc.c

using gcc 13.2.0 on Solaris 11.4.66 on x86-64.  (The original report came
from a gentoo Linux user, and I reproduced on Debian Linux, so this isn't
OS-specific.)

Adding -DUSE_SYSTEM_ASSERT to the compiler command line makes the warning
go away.

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