[Bug analyzer/102692] New: -Wanalyzer-null-dereference false alarm with (!p || q || !p->next)

["eggert at cs dot ucla.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102692

            Bug ID: 102692
           Summary: -Wanalyzer-null-dereference false alarm with (!p || q
                    || !p->next)
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: eggert at cs dot ucla.edu
  Target Milestone: ---

Created attachment 51588
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51588&action=edit
compile on x86-64 with "gcc -fanalyzer -O2 -S
analyzer-null-dereference-simple.i"

I ran into this problem when compiling GNU Emacs with gcc 11.2.1 20210728 (Red
Hat 11.2.1-1) on x86-64. Compile the attached simplified version with:

gcc -fanalyzer -O2 -S analyzer-null-dereference-simple.i

and the output will be as at the end of this description. This output is bogus
since it complains that 'tail' might be null in (!tail || end < prev ||
!tail->next) which means that tail->next might dereference a null pointer. But
the tail->next expression is obviously unreachable if 'tail' is null.

Although this bug might be related to GCC bug 102671, I'm filing it separately
as it has a different feel.