[Bug middle-end/54561] incorrect setjmp -Wclobber diagnostics

["mat at matws dot net" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54561

Matthieu Patou <mat at matws dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mat at matws dot net

--- Comment #3 from Matthieu Patou <mat at matws dot net> ---
I have more issues with Gcc generating wrong warning.
When trying to compile new dissectors with gcc 4.8.8 in wireshark I got:

/home/mat/workspace/wireshark/epan/dissectors/packet-dcerpc-dnsserver.c: In
function ‘dnsserver_dissect_struct_DNS_RPC_NAME_LIST’:

/home/mat/workspace/wireshark/epan/dissectors/packet-dcerpc-dnsserver.c:1902:23:
warning: variable ‘tmptree’ might be clobbered by ‘longjmp’ or ‘vfork’
[-Wclobbered]
  volatile proto_tree *tmptree = NULL;

/home/mat/workspace/wireshark/epan/dissectors/packet-dcerpc-dnsserver.c:1903:23:
warning: variable ‘tmpitem’ might be clobbered by ‘longjmp’ or ‘vfork’
[-Wclobbered]
  volatile proto_item *tmpitem = NULL;

The manpage of longjmp states that 

"The values of automatic variables are unspecified after a call to longjmp() if
they meet all the following criteria:

       ·  they are local to the function that made the corresponding setjmp(3)
call;
       ·  their values are changed between the calls to setjmp(3) and
longjmp(); and
       ·  they are not declared as volatile."

So without the volatile keyword the warning would valid but I explicitly
specified volatile to avoid this warning, unless I mis-understood something I
think this warning shouldn't be emitted.
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From: "su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/60578] New: wrong code (that hangs) at -O0 on x86_64-linux-gnu (affecting all gcc versions)
Date: Wed, 19 Mar 2014 05:17:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`578

            Bug ID: 60578
           Summary: wrong code (that hangs) at -O0 on x86_64-linux-gnu
                    (affecting all gcc versions)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -O0 in
64-bit mode (but not 32-bit).

It affects all GCC versions and seems to do with wrong integer promotion in the
expression "(c ^ 0L) < -1".

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20140318 (experimental) [trunk revision 208631] (GCC)
$
$ gcc-trunk -m32 -O0 small.c
$ a.out
$ gcc-trunk -m64 -O1 small.c
$ a.out
$
$ gcc-trunk -m64 -O0 small.c
$ a.out
^C
$


--------------------------


int a, *b = &a;

unsigned c;

int
foo ()
{
  return 0;
}

int
bar ()
{
  int i, j, m, n;
  *b = foo ();
  for (i = 0; i;)
    for (; j;)
      m = 0;
  if ((c ^ 0L) < -1)
    return 0;
  for (; n;)
    ;
  return 0;
}

int
main ()
{
  bar ();
  return 0;
}