[Bug c/28901] -Wunused-variable ignores unused const initialised variables

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28901

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Andrew Pinski from comment #3)
> From the code:
>        /* We don't warn about "static const" variables because the
> 	  "rcs_id" idiom uses that construction.  */

That is not a good reason not to warn:

[hjl@gnu-mic-2 gcc]$ cat /tmp/w.c
static const int foo[0x1000];
[hjl@gnu-mic-2 gcc]$ gcc  -Wall -S /tmp/w.c
[hjl@gnu-mic-2 gcc]$ cat w.s
    .file    "w.c"
    .local    foo
    .comm    foo,16384,32
    .ident    "GCC: (GNU) 4.8.2 20140115 (Red Hat 4.8.2-11)"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-mic-2 gcc]$ 

If we want to avoid rcs_id warning, we can check it explicitly and
not to warn it.
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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/55478] [devirt] trunk fails inline-devirt test #4
Date: Fri, 17 Jan 2014 00:42:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idU478

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|hubicka at gcc dot gnu.org         |unassigned at gcc dot gnu.org

--- Comment #12 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
print_length is not really a trivial wrapper:
void print_length (const String& string)
{
  for (uint64_t i = 0; i < string.length(); i++)
    {
      printf("%d\n", string.get(i));
    }
}

and the fact that it disappears depends on
 1) ability to inline it
 2) ability to devirtualize length and get calls
 3) ability to eliminate the loop since length is small.

Inlined can anticiapte 1-2 to happen, but not 3 and with -O2 it decides that
code size would grow.

For 3 one would need return functions to start with to determine the constant
bound. So we can get it better only once Martin gets to it ;)