[Bug c/25575] New: some uninitialized warning disappear when compile without -O

[Bug c/25575] New: some uninitialized warning disappear when compile without -O

[lidaobing at gmail dot com]

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Hello,

see example:

---->
$ cat warning.c
int main()
{
  int i;
  return i;
}
$ gcc -Wall warning.c
$ gcc -Wall -O0 warning.c
$ gcc -Wall -O warning.c
warning.c: In function ‘main’:
warning.c:4: warning: ‘i’ is used uninitialized in this function
warning.c
$ gcc -Wall -O1 warning.c
warning.c: In function ‘main’:
warning.c:4: warning: ‘i’ is used uninitialized in this function
$ gcc -Wall -O2 warning.c
warning.c: In function ‘main’:
warning.c:4: warning: ‘i’ is used uninitialized in this function
$ gcc -Wall -O3 warning.c
warning.c: In function ‘main’:
warning.c:4: warning: ‘i’ is used uninitialized in this function
$
<------


-- 
           Summary: some uninitialized warning disappear when compile
                    without -O
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: lidaobing at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25575

[Bug c/25575] some uninitialized warning disappear when compile without -O

[steven at gcc dot gnu dot org]

------- Comment #1 from steven at gcc dot gnu dot org  2005-12-27 12:22 -------
That happens because data flow information is used to find uninitialized
variables.  Some folks argue that this by itself is a bug, and that it should
be entirely up to the front end to diagnose uninitialized variables.  But then
a lot of warnings could not be issued because the front ends don't have the
means to compute which variables are initialized on one path through the
program but not on another.

In short, this is the result of a design decision.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25575

[Bug c/25575] some uninitialized warning disappear when compile without -O

[matze at braunis dot de]

------- Comment #2 from matze at braunis dot de  2007-06-18 14:17 -------
Why don't you turn on dataflow computation to get the warning even with -O0?
-O0 is typically used for developing/debugging, so as a user I want to see all
possible warnings...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25575