http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53990
Bug #: 53990
Summary: wrong "optimisation": automatic variable doesn't
removed at fuction exit
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: vol.li...@gmail.com
I use C++ with the following specs by g++ -v
Using built-in specs.
Target: x86_64-manbo-linux-gnu
Configured with: ../configure --prefix=/usr --libexecdir=/usr/lib
--with-slibdir=/lib64 --with-bugurl=https://qa.mandriva.com/
--mandir=/usr/share/man --infodir=/usr/share/info --enable-checking=release
--enable-languages=c,c++,ada,fortran,objc,obj-c++,java
--build=x86_64-manbo-linux-gnu --host=x86_64-manbo-linux-gnu --with-cpu=generic
--with-system-zlib --enable-threads=posix --enable-shared --enable-objc-gc
--enable-long-long --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-clocale=gnu --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-gtk-cairo
--disable-libjava-multilib --enable-ssp --disable-libssp --disable-werror
--with-ppl --with-cloog --with-python-dir=/lib/python2.6/site-packages
Thread model: posix
gcc version 4.4.1 (GCC)
I've also done tests with gcc version 4.4.5 (Debian 4.4.5-8) and gcc version
4.6.2 (SUSE Linux).
See the next code
struct A {
int d;
A operator*(const A&) const;
A operator+(const A&) const;
} a;
A A::operator*(const A& a) const {
A c;
c.d = d*a.d;
return c;
}
A A::operator+(const A& a) const {
cout << *this;
return a;
}
"return a;" causes the call of the copy constructor, but "return c;" doesn't
call this constructor---it returns (does not destroy!) automatic (!) variable
c. Is this optimization in C++ standard? If no then this optimisation may
cause severe errors if we are using pointers. See the next code.
#include
using namespace std;
struct Array {
unsigned char HSize, VSize;
int *p;
bool canBeDeleted;
Array(unsigned char, unsigned char);
Array(unsigned char, unsigned char, int*);
Array(const Array&);
Array operator[](unsigned char) const;
Array& operator=(const Array&);
Array& operator=(int);
Array operator+(Array) const;
friend ostream& operator<<(ostream&, const Array&);
operator int&() {return p[0];};
~Array();
};
Array::Array(unsigned char n, unsigned char m) {
VSize = n;
HSize = m;
p = new int[n*m];
canBeDeleted = true;
}
Array::Array(unsigned char n, unsigned char m, int* p1) {
VSize = n;
HSize = m;
p = p1;
canBeDeleted = true;
}
Array::Array(const Array& Data) {
HSize = Data.HSize;
VSize = Data.VSize;
p = new int[VSize*HSize];
for (int i = 0; i < Data.VSize; i++) {
for (int j = 0; j < Data.HSize; j++)
p[i*HSize + j] = Data.p[i*HSize + j];
}
canBeDeleted = true;
}
Array::~Array() {
if (canBeDeleted)
delete []p;
}
Array Array::operator[](unsigned char i) const {
if (i >= VSize && VSize != 1)
throw 1;
unsigned char size = HSize;
if (VSize == 1) {
size = 1;
if (i >= HSize)
throw 7;
}
Array A(1, size, p + i*size);
A.canBeDeleted = false;
return A;
}
Array& Array::operator=(int i) {
if (HSize != 1 && VSize != 1)
throw 2;
this->p[0] = i;
}
Array& Array::operator=(const Array& Data) {
if (VSize == Data.VSize && HSize == Data.HSize)
for (int i = 0; i < VSize; i++)
for (int j = 0; j < HSize; j++)
p[i*HSize + j] = Data.p[i*HSize + j];
else
throw 3;
return *this;
}
Array Array::operator+(Array Data) const {
if (VSize == Data.VSize && HSize == Data.HSize)
for (int i = 0; i < VSize; i++)
for (int j = 0; j < HSize; j++)
Data.p[i*HSize + j] += p[i*HSize + j];
else
throw 5;
return Data;
}
ostream& operator<<(ostream& s, const Array& Data) {
if (Data.VSize == 1 && Data.HSize == 1) {
s << Data.p[0];
return s;
}
s << endl;
for (int i = 0; i < Data.VSize; i++) {
for (int j = 0; j < Data.HSize; j++)
s << '\t' << Data.p[i*Data.HSize + j];
s << endl;
}
s << endl;
return s;
}
int main() {
Array A(3,3), E(3,3);
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++) {
E[i][j] = i == j;
A[i][j] = i + j;
}
cout << "A" << A << "E" << E;
A[1][2] = 7;
A[2] = E[1]; //it works. but should it work?
A[1] + E[2]; //a problem!
cout << "E" << E;
}
E was changed! :-(
Regards
Litwr
