[Bug middle-end/36550] Wrong may be used uninitialized warning (conditional PHIs)

[corinl at gmx dot de]

--- Comment #9 from corinl at gmx dot de  2009-02-12 21:53 ---
I do not really understand problem 5 for the case when the only dependancy for
the code-path check is a local variable. In this case the value cannot be
change by any other code than existing between the two checks, so this case
should be handled reliable for sure. Of course this is not possible with global
oder class variables which might be affected by some other thread.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36550

[Bug c++/39133] wrong optimization produces output of false warning

[corinl at gmx dot de]

--- Comment #3 from corinl at gmx dot de  2009-02-12 07:26 ---
Thanks for the info. Unluckily I just found the bug reported first now for
sure:

Code:

// setuid/setgid only affect the current thread
#define FS_PERMS_SET(_uid, _gid) \
bool check_permissions_local = check_permissions; \
uid_t fs_perms_uid_orig; \
gid_t fs_perms_gid_orig; \
if (check_permissions_local) \
{ \
fs_perms_uid_orig = setfsuid(_uid); \
fs_perms_gid_orig = setfsgid(_gid); \
}

// setuid/setgid only affect the current thread
#define FS_PERMS_RESTORE() \
if (check_permissions_local) \
{ \
setfsuid(fs_perms_uid_orig); \
setfsgid(fs_perms_gid_orig); \
}

#define FOP_ERRNO(R) out-op_errno=((R==0)?0:errno)

...
line 934:
FS_PERMS_SET(in-uid, in-gid);

FOP_ERRNO(statvfs(path, out-stbuf));

FS_PERMS_RESTORE();
...

Error report:

main.cpp:934: Warnung: »fs_perms_gid_orig« könnte in dieser Funktion
uninitialisiert verwendet werden
main.cpp:934: Warnung: »fs_perms_uid_orig« könnte in dieser Funktion
uninitialisiert verwendet werden

This is not true, as at this point the variables are only written to. They are
only ever read (and even later) if they have first been written to.


-- 

corinl at gmx dot de changed:

   What|Removed |Added

 Status|RESOLVED|UNCONFIRMED
 Resolution|FIXED   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39133

[Bug c++/39133] wrong optimization produces output of false warning

[corinl at gmx dot de]

--- Comment #4 from corinl at gmx dot de  2009-02-12 07:37 ---
here's the copy from the precompiled header file (.ii), may be it helps:
(check_permissions_local removed, it was just for test..same error as before)

 uid_t fs_perms_uid_orig; gid_t fs_perms_gid_orig; if (check_permissions) {
fs_perms_uid_orig = setfsuid(in-uid); fs_perms_gid_orig = setfsgid(in-gid);
};

 out-op_errno=((statvfs(path, out-stbuf)==0)?0:(*__errno_location ()));

 if (check_permissions) { setfsuid(fs_perms_uid_orig);
setfsgid(fs_perms_gid_orig); };


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39133

[Bug c++/39133] New: wrong optimization produces output of false warning

[corinl at gmx dot de]

piece of code inside contained in class methode (starting line 263):
---
char *buf;
if (!strncmp(in-loc.path,/translators/,strlen(/translators/)))
{
translator_c *xl = translator_from_path(in-loc.path);
if (xl)
{
char *loc =
in-loc.path+strlen(/translators/)+strlen(xl-name);
LOG_DEBUG(log, control_get_data, xl '%s', loc '%s', xl-name,
loc);
buf = xl-control_get_data(loc);
}
}
else
{
char *loc = in-loc.path;
LOG_DEBUG(log, control_get_data, internal, loc '%s', loc);
buf = control_get_data(loc);
}

if (buf)
{
MEM_NEW(persistent, persistent_c());
persistent-read_mode = true;
persistent-data = buf;
persistent-data_len = strlen(persistent-data);

out-ref = (xl_ref_t) persistent;
out-op_errno = 0;
}
else
{
out-op_errno = ENOENT;
}
---


compiling with the following options works fine (no warnings, no errors):
---
CFLAGS=-Wall -Werror -fPIC -pthread -I../common -I../../common
-I../../../common -I../shared -I../../shared -I../../../shared -O0 -g
---


compiling with the following options produces a warning (=error);
---
CFLAGS=-Wall -Werror -fPIC -pthread -I../common -I../../common
-I../../../common -I../shared -I../../shared -I../../../shared -O3 -ffast-math
---
cc1plus: warnings being treated as errors
main.cpp: In member function »virtual void main_c::fop_open(stack_frame_t*)«:
main.cpp:263: Warnung: »buf« könnte in dieser Funktion uninitialisiert
verwendet werden
make: *** [main.o] Fehler 1
---
Fehler = Error
»buf« könnte in dieser Funktion uninitialisiert verwendet werden = buf could
be used uninitialized in this function
---

as you can clearly see, buf could never be used uninitialized so this must be a
compiler/optimizer bug.


-- 
   Summary: wrong optimization produces output of false warning
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: corinl at gmx dot de
 GCC build triplet: 4.2.3-2ubuntu7
  GCC host triplet: x86_64
GCC target triplet: x86_64


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39133

[Bug c++/39133] wrong optimization produces output of false warning

[corinl at gmx dot de]

--- Comment #1 from corinl at gmx dot de  2009-02-08 22:07 ---
Oh sorry, I just see that buf could be used uninitialized for sure (if
xl==NULL). but well, shouldn't this warning then be issued all the times? so
the bug is now reversed - missing warning instead of false warning ;)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39133