[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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=gccview=revrev=138933 Log: 2008-08-10 Manuel Lopez-Ibanez [EMAIL PROTECTED] 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
-- gdr at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Last reconfirmed|-00-00 00:00:00 |2005-11-26 07:38:31 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- 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
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-03-26 00:43 --- I think we had decided even though the code is unreachable, we want to warn about this. -- What|Removed |Added Component|c++ |middle-end Keywords||diagnostic http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- Additional Comments From sebor at roguewave dot com 2005-03-26 01:08 --- I can imagine that it may not be straightforward to fix but I can't think of a reason why a warning could ever be useful in this case (i.e., when the code is provably safe). I could of course be missing something -- could you point me to the discussion where this was decided? Thanks! -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
[Bug middle-end/20644] bogus uninitialized warning on unused variable
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-03-26 01:13 --- (In reply to comment #2) I can imagine that it may not be straightforward to fix but I can't think of a reason why a warning could ever be useful in this case (i.e., when the code is provably safe). I could of course be missing something -- could you point me to the discussion where this was decided? Thanks! Actually in 4.0.0 and above, it is an easy fix, just moving around the order around of the passes. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20644
