For the attached testcase, g++ gives a warning saying "`z' is used
uninitialized in this function" (_is_ used uninitialized, not _may be_ used
uninitialized)
in the statement marked with (***) below. However, `z' is indeed
initialized by the mul() function template, which takes the first
argument by (non-const) reference:
template <typename To_Policy, typename From1_Policy, typename From2_Policy,
typename Type>
inline Result
add_mul_int(Type& to, const Type x, const Type y, Rounding_Dir dir) {
Type z;
Result r = mul<To_Policy, From1_Policy, From2_Policy>(z, x, y, dir);
switch (r) {
case V_NEG_OVERFLOW:
case V_LT:
if (to <= 0) {
to = z; (***)
return r;
}
To reproduce:
$ bunzip2 bug.cc.bz2
$ md5sum bug.cc
bb3e86d1d865d1b661dd86da3456c909 bug.cc
$ g++ -Wall -O2 -c bug.cc
bug.cc: In function void
Parma_Polyhedra_Library::add_mul_assign(Parma_Polyhedra_Library::Checked_Number<T,
P>&, const Parma_Polyhedra_Library::Checked_Number<T, P>&, const
Parma_Polyhedra_Library::Checked_Number<T, P>&) [with T = long int, Policy =
Parma_Polyhedra_Library::Checked_Number_Default_Policy]:
bug.cc:37941: warning: z is used uninitialized in this function
$ g++ -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic
--host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20070626 (Red Hat 4.1.2-13)
$
The file bug.cc.t28.ssa is 944683 bytes once compressed: I will attach it if
required.
--
Summary: g++ says `z' is used uninitialized but this is not true
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bagnara at cs dot unipr dot it
GCC host triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33802
