(Repeating my comment on the GDB bugzilla here)

All these warnings are around setjmp/longjmp.

E.g, with:

.././../src/gdb/python/py-framefilter.c:731:11: error: ‘local_indent’ may be
used uninitialized in this function [-Werror=maybe-uninitialized]
       int local_indent = 8 + (8 * indent);

local_indent is only used in a TRY_CATCH block, meaning, after a setjmp.

I suspect this to be related to this recent setjmp gcc change:

 http://gcc.gnu.org/ml/gcc-patches/2013-05/msg00344.html

Please attach at least one example as preprocessed source.

hmb,

could you do that?

See instructions here: http://gcc.gnu.org/bugs/

I am attaching the all preprocessed source code of GDB
here is the link https://www.dropbox.com/s/ldml34p3lov867w/gcc-bug.zip

Confirmed with -O2 -Wall.

Created attachment 30172 [details]
preprocessed source

tree-ssa-uninit.c somehow fails to properly handle abnormal edges.

Index: tree-ssa-uninit.c
===================================================================
--- tree-ssa-uninit.c   (revision 199249)
+++ tree-ssa-uninit.c   (working copy)
@@ -1919,7 +1919,8 @@ find_uninit_use (gimple phi, unsigned un
             }
 
           worklist->safe_push (use_stmt);
-          pointer_set_insert (possibly_undefined_names, phi_result);
+         if (!SSA_NAME_OCCURS_IN_ABNORMAL_PHI (phi_result))
+           pointer_set_insert (possibly_undefined_names, phi_result);
         }
     }
 
fixes the issue but that doesn't look the very best place to fix it
and it doesn't look fully correct.  It should be enough to not consider
values flowing across abnormal edges - but that's already done (but somehow
not in a complete manner).

I'm trying to reduce the testcase to get a better idea what is going wrong
here.

Created attachment 30175 [details]
somewhat reduced testcase

Autoreduced on level 0.

Created attachment 30176 [details]
more reduced

#include <setjmp.h>
jmp_buf buf;
void foo (int);
void bar (int) __attribute__((leaf));
void enumerate_locals (int indent)
{
  foo (0);
  while (indent--)     
    {
      int local_indent = 8 + (8 * indent);
      if (local_indent != 8)
        {
          setjmp (buf);
          bar (local_indent);
        }
    }
  foo (1);
}


warns about uninitialized local_indent.  The abnormal edges we insert
for foo (0) make undefined values flow into the setjmp block.

Author: rguenth
Date: Fri May 24 12:44:58 2013
New Revision: 199289

URL: http://gcc.gnu.org/viewcvs?rev=199289&root=gcc&view=rev
Log:
2013-05-24  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/57287
	* tree-ssa-uninit.c (compute_uninit_opnds_pos): Disregard
	all SSA names that occur in abnormal PHIs.

	* gcc.dg/pr57287.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/pr57287.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-uninit.c

I got enother error in gdb source code with same building step as I described above:

/home/mbilal/gcc-svn/install/bin/gcc -save-temps -g -O2   -I. -I.././../src/gdb -I.././../src/gdb/common -I.././../src/gdb/config -DLOCALEDIR="\"/home/mbilal/gdb-git/gcc_install_bug_report/share/locale\"" -DHAVE_CONFIG_H -I.././../src/gdb/../include/opcode -I.././../src/gdb/../opcodes/.. -I.././../src/gdb/../readline/.. -I../bfd -I.././../src/gdb/../bfd -I.././../src/gdb/../include -I../libdecnumber -I.././../src/gdb/../libdecnumber  -I.././../src/gdb/gnulib/import -Ibuild-gnulib/import   -DTUI=1  -I/usr/include/python2.7 -I/usr/include/python2.7 -Wall -Wdeclaration-after-statement -Wpointer-arith -Wpointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wmissing-prototypes -Wdeclaration-after-statement -Wempty-body -Wformat-nonliteral -Werror -c -o value.o -MT value.o -MMD -MP -MF .deps/value.Tpo .././../src/gdb/value.c
.././../src/gdb/value.c: In function ‘show_convenience’:
.././../src/gdb/value.c:2247:21: error: ‘buf’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
       TRY_CATCH (ex, RETURN_MASK_ERROR)
                     ^
cc1: all warnings being treated as errors
make[2]: *** [value.o] Error 1
make[2]: Leaving directory `/home/mbilal/gdb-git/gcc-obj_bug_report/gdb'
make[1]: *** [all-gdb] Error 2
make[1]: Leaving directory `/home/mbilal/gdb-git/gcc-obj_bug_report'
make: *** [all] Error 2

Created attachment 30201 [details]
preprocessed source code

Attaching the preprocessed source code

(In reply to hmb from comment #13)
> Created attachment 30201 [details]
> preprocessed source code
> 
> Attaching the preprocessed source code

Here is a reduction (as of trunk today):

$ cat test.c
#include <setjmp.h>
#include <stdio.h>

struct node
{
  struct node *next;
  char *name;
} *list;

struct node *list;
struct node *head (void);

sigjmp_buf *bar (void);

int baz (void)
{
  struct node *n;
  int varseen = 0;

  list = head ();
  for (n = list; n; n = n->next)
    {
      if (!varseen)
          varseen = 1;

      sigjmp_buf *buf = bar ();
      __sigsetjmp (*buf, 1);
    }

  if (!varseen)
    return 0;
  return 1;
}
$ i686-pc-linux-gnu-gcc --version
i686-pc-linux-gnu-gcc (GCC) 4.9.0 20130819 (experimental)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ i686-pc-linux-gnu-gcc -Wall -O2 -c test.c
test.c: In function 'baz':
test.c:26:19: warning: 'buf' may be used uninitialized in this function [-Wmaybe-uninitialized]
       sigjmp_buf *buf = bar ();
                   ^

Confirmed.  David, can you have a look here?  I had a hard time following what
exactly to do with the dataflow in the uninit pass for abnormal control flow
(abnormal control flow should be considered receiving an initialized value).

Thanks.

(In reply to Richard Biener from comment #15)
> Confirmed.  David, can you have a look here?  I had a hard time following
> what
> exactly to do with the dataflow in the uninit pass for abnormal control flow
> (abnormal control flow should be considered receiving an initialized value).
> 
> Thanks.


I looked at it a little. The warning is not from the predicated uninit analysis which checks uses of phi defs.  The warning is emitted from tree-ssa.c:1644 in function warn_uninitialized_vars. It warns about the 'definitely' uninitialized variable that may be executed. In this case it is use of 'buf_16(ab)' in BB3.  Not sure where this statement comes from:

buf_24 = buf_16(ab);

The dot file is attached.

digraph "uninit.c.131t.uninit1" {
overlap=false;
subgraph "baz" {
	color="black";
	label="baz";
	fn_11_basic_block_0 [shape=Mdiamond,style=filled,fillcolor=white,label="ENTRY"];

	fn_11_basic_block_1 [shape=Mdiamond,style=filled,fillcolor=white,label="EXIT"];

	fn_11_basic_block_2 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:10000 |\<bb\ 2\>:\l\
|varseen_11(ab)\ =\ 0;\l\
|_14\ =\ head\ ();\l\
}"];

	fn_11_basic_block_3 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:7100 |\<bb\ 3\>:\l\
|list\ =\ _14;\l\
|buf_24\ =\ buf_16(ab);\l\
|if\ (_14\ !=\ 0B)\l\
\ \ goto\ \<bb\ 4\>;\l\
else\l\
\ \ goto\ \<bb\ 8\>;\l\
}"];

	fn_11_basic_block_4 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:8500 |\<bb\ 4\>:\l\
|#\ varseen_3(ab)\ =\ PHI\ \<1(3),\ 1(6)\>\l\
|#\ n_26(ab)\ =\ PHI\ \<_14(3),\ n_2(ab)(6)\>\l\
|#\ buf_27(ab)\ =\ PHI\ \<buf_24(3),\ buf_7(ab)(6)\>\l\
|buf_21\ =\ bar\ ();\l\
}"];

	fn_11_basic_block_5 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:4250 |\<bb\ 5\>:\l\
}"];

	fn_11_basic_block_6 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:2900 |\<bb\ 6\>:\l\
|#\ n_1(ab)\ =\ PHI\ \<n_15(ab)(2),\ n_26(ab)(4),\ n_26(ab)(5)\>\l\
|#\ varseen_4(ab)\ =\ PHI\ \<varseen_11(ab)(2),\ varseen_3(ab)(4),\ varseen_3(ab)(5)\>\l\
|#\ buf_6(ab)\ =\ PHI\ \<buf_16(ab)(2),\ buf_27(ab)(4),\ buf_21(5)\>\l\
|__sigsetjmp\ (buf_6(ab),\ 1);\l\
|n_19\ =\ n_1(ab)-\>next;\l\
|n_2(ab)\ =\ n_19;\l\
|varseen_5\ =\ varseen_4(ab);\l\
|buf_7(ab)\ =\ buf_6(ab);\l\
|if\ (n_2(ab)\ !=\ 0B)\l\
\ \ goto\ \<bb\ 4\>;\l\
else\l\
\ \ goto\ \<bb\ 7\>;\l\
}"];

	fn_11_basic_block_7 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:1500 |\<bb\ 7\>:\l\
|_25\ =\ varseen_5;\l\
}"];

	fn_11_basic_block_8 [shape=record,style=filled,fillcolor=lightgrey,label="{ FREQ:1500 |\<bb\ 8\>:\l\
|#\ _8\ =\ PHI\ \<_25(7),\ 0(3)\>\l\
|return\ _8;\l\
}"];

	fn_11_basic_block_0:s -> fn_11_basic_block_2:n [style="solid,bold",color=blue,weight=100,constraint=true, label="[100%]"];
	fn_11_basic_block_2:s -> fn_11_basic_block_6:n [style="solid,bold",color=red,weight=10,constraint=true, label="[29%]"];
	fn_11_basic_block_2:s -> fn_11_basic_block_3:n [style="solid,bold",color=blue,weight=100,constraint=true, label="[71%]"];
	fn_11_basic_block_3:s -> fn_11_basic_block_4:n [style="solid,bold",color=black,weight=10,constraint=true, label="[85%]"];
	fn_11_basic_block_3:s -> fn_11_basic_block_8:n [style="solid,bold",color=black,weight=10,constraint=true, label="[15%]"];
	fn_11_basic_block_4:s -> fn_11_basic_block_6:n [style="dotted,bold",color=red,weight=10,constraint=false, label="[50%]"];
	fn_11_basic_block_4:s -> fn_11_basic_block_5:n [style="solid,bold",color=blue,weight=100,constraint=true, label="[50%]"];
	fn_11_basic_block_5:s -> fn_11_basic_block_6:n [style="dotted,bold",color=blue,weight=10,constraint=false, label="[100%]"];
	fn_11_basic_block_6:s -> fn_11_basic_block_4:n [style="solid,bold",color=black,weight=10,constraint=true, label="[85%]"];
	fn_11_basic_block_6:s -> fn_11_basic_block_7:n [style="solid,bold",color=black,weight=10,constraint=true, label="[15%]"];
	fn_11_basic_block_7:s -> fn_11_basic_block_8:n [style="solid,bold",color=blue,weight=100,constraint=true, label="[100%]"];
	fn_11_basic_block_8:s -> fn_11_basic_block_1:n [style="solid,bold",color=black,weight=10,constraint=true, label="[100%]"];
	fn_11_basic_block_0:s -> fn_11_basic_block_1:n [style="invis",constraint=true];
}
}

(In reply to davidxl from comment #16)
> (In reply to Richard Biener from comment #15)
> > Confirmed.  David, can you have a look here?  I had a hard time following
> > what
> > exactly to do with the dataflow in the uninit pass for abnormal control flow
> > (abnormal control flow should be considered receiving an initialized value).
> > 
> > Thanks.
> 
> 
> I looked at it a little. The warning is not from the predicated uninit
> analysis which checks uses of phi defs.  The warning is emitted from
> tree-ssa.c:1644 in function warn_uninitialized_vars. It warns about the
> 'definitely' uninitialized variable that may be executed. In this case it is
> use of 'buf_16(ab)' in BB3.  Not sure where this statement comes from:
> 
> buf_24 = buf_16(ab);

Oh, sorry for not looking close enough again.  It is jump-threading introducing
this copy by duplicating a block with an abnormal PHI.

Not sure why it chooses to duplicate it - I see no jump threads registered
by DOM at -O1 - probably because:

  if (dump_file && (dump_flags & TDF_DETAILS)
      && e->dest != e2->src)
    fprintf (dump_file,
             "  Registering jump thread around one or more intermediate blocks\n");

(gdb) p threaded_edges.vec_->vecdata_[0]->dest
$7 = <basic_block 0x7ffff6e1a4e0 (9)>
(gdb) p threaded_edges.vec_->vecdata_[1]->src
$8 = <basic_block 0x7ffff6e1a4e0 (9)>

but thats the jump threading it performs as it can optimize the if (!varseen)
check.

From looking at the symptoms - warning about buf_16(D)(ab) use in

  buf_24 = buf_16(D)(ab);

it seems simplest to disregard SSA names occuring in abnormal PHIs ...

Author: rguenth
Date: Thu Aug 29 11:20:16 2013
New Revision: 202069

URL: http://gcc.gnu.org/viewcvs?rev=202069&root=gcc&view=rev
Log:
2013-08-29  Richard Biener  <rguenther@suse.de>

	PR middle-end/57287
	* tree-ssa-copy.c (may_propagate_copy): Allow propagating
	of default defs that appear in abnormal PHI nodes.

	* gcc.dg/pr57287-2.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/pr57287-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-copy.c

Fixed again.

Confirmed fix.

I can also now build GDB trunk with GCC trunk (both from today).

Thanks Richard!

(In reply to Richard Biener from comment #18)

> Added:
>     trunk/gcc/testsuite/gcc.dg/pr57287-2.c

Why is that using __sigsetjmp ?  That's not a standard function.
E.g. newlib doesn't have it.

On Tue, 3 Sep 2013, amylaar at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57287
> 
> Jorn Wolfgang Rennecke <amylaar at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |amylaar at gcc dot gnu.org
> 
> --- Comment #21 from Jorn Wolfgang Rennecke <amylaar at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #18)
> 
> > Added:
> >     trunk/gcc/testsuite/gcc.dg/pr57287-2.c
> 
> Why is that using __sigsetjmp ?  That's not a standard function.
> E.g. newlib doesn't have it.

Sorry, I forgot to change it to setjmp.  Done now.

Author: rguenth
Date: Tue Sep  3 07:53:05 2013
New Revision: 202197

URL: http://gcc.gnu.org/viewcvs?rev=202197&root=gcc&view=rev
Log:
2013-09-03  Richard Biener  <rguenther@suse.de>

	PR middle-end/57287
	* gcc.dg/pr57287-2.c: Use setjmp, not __sigsetjmp.

Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/pr57287-2.c