[Bug tree-optimization/104060] New: -Wmaybe-uninitialized false alarm on address of local array

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104060

            Bug ID: 104060
           Summary: -Wmaybe-uninitialized false alarm on address of local
                    array
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eggert at cs dot ucla.edu
  Target Milestone: ---

Created attachment 52209
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52209&action=edit
compile with 'gcc -Wuninitialized' to see the false alarm

I ran into this problem when compiling an experimental version of GNU coreutils
with gcc 11.2.1 20211203 (Red Hat 11.2.1-7), x86-64.

This is a regression, since gcc 8.5.0 20210514 (Red Hat 8.5.0-4) does not have
the problem.

Compile the attached program with 'gcc -Wuninitialized -S
false-alarm-uninit.c'. There should be no output, but GCC outputs the
following. The diagnostic is incorrect, as bin_buffer_unaligned is an array
that is never read from or written to. Apparently GCC is getting confused
because the array's address is taken (but that address is never dereferenced).

false-alarm-uninit.c: In function ‘digest_check’:
false-alarm-uninit.c:13:31: warning: ‘bin_buffer_unaligned’ may be used
uninitialized [-Wmaybe-uninitialized]
   13 |   unsigned char *bin_buffer = ptr_align (bin_buffer_unaligned, 1024);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
false-alarm-uninit.c:2:1: note: by argument 1 of type ‘const void *’ to
‘ptr_align’ declared here
    2 | ptr_align (void const *ptr, unsigned long alignment)
      | ^~~~~~~~~
false-alarm-uninit.c:12:17: note: ‘bin_buffer_unaligned’ declared here
   12 |   unsigned char bin_buffer_unaligned[10000];
      |                 ^~~~~~~~~~~~~~~~~~~~