* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
@ 2005-11-02 19:52 ` h dot b dot furuseth at usit dot uio dot no
2005-11-08 17:23 ` law at redhat dot com
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From: h dot b dot furuseth at usit dot uio dot no @ 2005-11-02 19:52 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from h dot b dot furuseth at usit dot uio dot no 2005-11-02 19:52 -------
I think I'd appreciate that warning when writing portable code:
The warning can be useful if the 1 is replaced with a macro
which may or may not expand to 1, or an enum defined in an #ifdef,
or an implementation-dependent expression like ((char)-1 < 0).
But of course, it depends on how many false positives the warning
tends to give for normal programs.
Maybe there could be a warning option to turn on and off some
warnings that do not apply with the particular #defines and
constants being used. (And also turn on/off -Wunreachable
for this case.)
--
h dot b dot furuseth at usit dot uio dot no changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |h dot b dot furuseth at usit
| |dot uio dot no
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
2005-11-02 19:52 ` [Bug middle-end/20644] bogus uninitialized warning on unused variable h dot b dot furuseth at usit dot uio dot no
@ 2005-11-08 17:23 ` law at redhat dot com
2005-11-08 17:26 ` pinskia at gcc dot gnu dot org
` (6 subsequent siblings)
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From: law at redhat dot com @ 2005-11-08 17:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from law at redhat dot com 2005-11-08 17:23 -------
Bogus warning no longer issued with GCC 4.1 based compilers.
--
law at redhat dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |FIXED
Target Milestone|--- |4.1.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
2005-11-02 19:52 ` [Bug middle-end/20644] bogus uninitialized warning on unused variable h dot b dot furuseth at usit dot uio dot no
2005-11-08 17:23 ` law at redhat dot com
@ 2005-11-08 17:26 ` pinskia at gcc dot gnu dot org
2005-11-26 7:38 ` gdr at gcc dot gnu dot org
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From: pinskia at gcc dot gnu dot org @ 2005-11-08 17:26 UTC (permalink / raw)
To: gcc-bugs
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------- Comment #6 from pinskia at gcc dot gnu dot org 2005-11-08 17:25 -------
(In reply to comment #5)
> Bogus warning no longer issued with GCC 4.1 based compilers.
Huh:
gcc version 4.1.0 20051106 (experimental)
../t6.c: In function foo:
../t6.c:13: warning: j is used uninitialized in this function
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |UNCONFIRMED
Resolution|FIXED |
Target Milestone|4.1.0 |---
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (2 preceding siblings ...)
2005-11-08 17:26 ` pinskia at gcc dot gnu dot org
@ 2005-11-26 7:38 ` gdr at gcc dot gnu dot org
2007-08-20 14:18 ` manu at gcc dot gnu dot org
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From: gdr at gcc dot gnu dot org @ 2005-11-26 7:38 UTC (permalink / raw)
To: gcc-bugs
--
gdr at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2005-11-26 07:38:31
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (3 preceding siblings ...)
2005-11-26 7:38 ` gdr at gcc dot gnu dot org
@ 2007-08-20 14:18 ` manu at gcc dot gnu dot org
2007-08-22 17:38 ` manu at gcc dot gnu dot org
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From: manu at gcc dot gnu dot org @ 2007-08-20 14:18 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from manu at gcc dot gnu dot org 2007-08-20 14:18 -------
Even simpler testcase:
int foo ()
{
int i = 0;
int j;
if (1 == i)
return j;
return 0;
}
This will only be reliably fixed by building a better SSA representation.
Moving the passes around will just solve it by chance (because CCP will assume
that j undefined value is actually 0, and thus remove j). Also, it will silence
many warnings (for the same reason, CCP happily initializing uninitialized
variables)
So instead of:
foo ()
{
int j;
int i;
int D.1280;
<bb 0>:
[pr20644.c : 3] i_2 = 0;
[pr20644.c : 6] if ([pr20644.c : 6] i_2 == 1) goto <L0>; else goto <L1>;
<L0>:;
[pr20644.c : 7] D.1280_6 = j_5;
[pr20644.c : 7] goto <bb 3> (<L2>);
<L1>:;
[pr20644.c : 9] D.1280_4 = 0;
# D.1280_1 = PHI <D.1280_6(1), D.1280_4(2)>;
<L2>:;
return D.1280_1;
}
We could generate:
foo ()
{
int j;
int i;
<bb 0>:
[pr20644.c : 3] i_2 = 0;
[pr20644.c : 6] if ([pr20644.c : 6] i_2 == 1) goto <L0>; else goto <L1>;
<L0>:;
[pr20644.c : 7] goto <bb 3> (<L2>);
<L1>:;
[pr20644.c : 9] j_6 = 0;
# j_7 = PHI <j_5(D), j_6(2)>;
<L2>:;
return j_7;
}
--
manu at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (4 preceding siblings ...)
2007-08-20 14:18 ` manu at gcc dot gnu dot org
@ 2007-08-22 17:38 ` manu at gcc dot gnu dot org
2007-08-23 14:17 ` manu at gcc dot gnu dot org
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From: manu at gcc dot gnu dot org @ 2007-08-22 17:38 UTC (permalink / raw)
To: gcc-bugs
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------- Comment #8 from manu at gcc dot gnu dot org 2007-08-22 17:38 -------
(In reply to comment #6)
> (In reply to comment #5)
> gcc version 4.1.0 20051106 (experimental)
> ../t6.c: In function foo:
> ../t6.c:13: warning: j is used uninitialized in this function
>
Despite what I said before, for this particular case, we should never give a
"is used" warning if the BB is not executed with 100% probability. Hmm, I'll
check whether we can detect this.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (5 preceding siblings ...)
2007-08-22 17:38 ` manu at gcc dot gnu dot org
@ 2007-08-23 14:17 ` manu at gcc dot gnu dot org
2008-08-10 18:48 ` manu at gcc dot gnu dot org
2008-08-10 19:50 ` manu at gcc dot gnu dot org
8 siblings, 0 replies; 12+ messages in thread
From: manu at gcc dot gnu dot org @ 2007-08-23 14:17 UTC (permalink / raw)
To: gcc-bugs
------- Comment #9 from manu at gcc dot gnu dot org 2007-08-23 14:17 -------
(In reply to comment #8)
> Despite what I said before, for this particular case, we should never give a
> "is used" warning if the BB is not executed with 100% probability. Hmm, I'll
> check whether we can detect this.
We could avoid the warning by doing the following:
--- gcc/tree-ssa.c (revision 126606)
+++ gcc/tree-ssa.c (working copy)
@@ -1302,8 +1334,11 @@
}
}
static unsigned int
execute_early_warn_uninitialized (void)
{
block_stmt_iterator bsi;
basic_block bb;
FOR_EACH_BB (bb)
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- {
- tree context = bsi_stmt (bsi);
- walk_tree (bsi_stmt_ptr (bsi), warn_uninitialized_var,
- context, NULL);
- }
+ {
+ edge e;
+ edge_iterator ei;
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ if (e->flags & EDGE_FALLTHRU)
+ {
+ for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+ {
+ tree context = bsi_stmt (bsi);
+ walk_tree (bsi_stmt_ptr (bsi), warn_uninitialized_var,
+ context, NULL);
+ }
+ break;
+ }
+ }
I think this is the "Right Thing To Do". Otherwise, we are giving "is used"
warnings for BBs that are conditionally executed. On the other hand, we will
miss a few of the correct warnings that we get by chance by not doing the
"Right Thing".
Comments?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (6 preceding siblings ...)
2007-08-23 14:17 ` manu at gcc dot gnu dot org
@ 2008-08-10 18:48 ` manu at gcc dot gnu dot org
2008-08-10 19:50 ` manu at gcc dot gnu dot org
8 siblings, 0 replies; 12+ messages in thread
From: manu at gcc dot gnu dot org @ 2008-08-10 18:48 UTC (permalink / raw)
To: gcc-bugs
------- Comment #10 from manu at gcc dot gnu dot org 2008-08-10 18:47 -------
Subject: Bug 20644
Author: manu
Date: Sun Aug 10 18:46:10 2008
New Revision: 138933
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=138933
Log:
2008-08-10 Manuel Lopez-Ibanez <manu@gcc.gnu.org>
PR middle-end/20644
* tree-ssa.c (struct walk_data): Add new flag
warn_possibly_uninitialized.
(warn_uninitialized_var): Use it.
(warn_uninitialized_vars): New.
(execute_early_warn_uninitialized): Call it.
(execute_late_warn_uninitialized): Likewise.
testsuite/
* gcc.dg/uninit-pr20644-O0.c: New.
* gcc.dg/uninit-pr20644.c: New.
Added:
trunk/gcc/testsuite/gcc.dg/uninit-pr20644-O0.c
trunk/gcc/testsuite/gcc.dg/uninit-pr20644.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/testsuite/ChangeLog
trunk/gcc/tree-ssa.c
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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* [Bug middle-end/20644] bogus uninitialized warning on unused variable
[not found] <bug-20644-1186@http.gcc.gnu.org/bugzilla/>
` (7 preceding siblings ...)
2008-08-10 18:48 ` manu at gcc dot gnu dot org
@ 2008-08-10 19:50 ` manu at gcc dot gnu dot org
8 siblings, 0 replies; 12+ messages in thread
From: manu at gcc dot gnu dot org @ 2008-08-10 19:50 UTC (permalink / raw)
To: gcc-bugs
------- Comment #11 from manu at gcc dot gnu dot org 2008-08-10 19:48 -------
This is FIXED in GCC 4.4. This may have fixed other uninitialized PRs, so if
you have reported one, please recheck with the a recent 4.4 revision
--
manu at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
Target Milestone|--- |4.4.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
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