------- Comment #1 from manu at gcc dot gnu dot org 2010-03-14 15:45 -------
In GCC 4.3.x you need optimization enabled for Wuninitialized.
In GCC 4.4.1 and GCC 4.5 (trunk) I get warnings in line 6 with -O1 -O2 and -O3.
We do not get a warning with -O0 because the default definition appears in a
PHI node:
<bb 2>:
[pr43361.C : 6 : 3] goto <bb 4>;
<bb 3>:
[pr43361.C : 7:19] std::basic_ostream<char>::operator<< ([pr43361.C : 7]
&cout, i_1);
[pr43361.C : 8:18] [pr43361.C : 8] array[i_1] = i_1;
[pr43361.C : 6:3] i_4 = i_1 + 1;
<bb 4>:
# i_1 = PHI <i_2(D)(2), [pr43361.C : 6:3] i_4(3)>
[pr43361.C : 6:3] D.21125_3 = i_1 <= 9;
[pr43361.C : 6:3] if (D.21125_3 != 0)
goto <bb 3>;
else
goto <bb 5>;
<bb 5>:
[pr43361.C : 0:0] D.21127_5 = 0;
return D.21127_5;
This can be seen as a natural limitation of the analysis at -O0 or a problem
with the way GCC represents loops:
for (init; test; next) { for-body }; is transformed to:
init:
init;
goto eval
body:
for-body;
next;
goto eval;
eval:
(test) ? goto body : goto finish;
finish:
So, although we know what "test" is evaluated at least once after init, GCC
doesn't know that with -O0.
In any case, there is no trivial fix (but there is a workaround: use
optimization).
--
manu at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu dot org
OtherBugsDependingO| |24639
nThis| |
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2010-03-14 15:45:50
date| |
Summary|[g++-4.3..g++-4.5] for-loops|missing uninitialzied
|are in the way of |warning without optimization
|Wuninitialized? |(loop representation)
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43361
