On Aug 10, 2010, at 1:00 AM, "attardi at di dot unipi dot it" <gcc-bugzi...@gcc.gnu.org
> wrote:
Code produced using -O2 handles dereferencing incorrectly.
Here is a program that shows the bug:
#include <iostream>
#include <vector>
class Derived : public std::vector<char *>
{
public:
Derived() {}
};
void* foo(void* arg) {
void* baseptr = 0;
*(std::vector<char*> **)&baseptr = (Derived *)arg;
return baseptr;
}
Have it do
jlong a = 0;
memcpy(&a, &arg, sizeof(void*));
That is the most portable way of putting a pointer value in jlong.
void* foo2(void* arg) {
void* baseptr = 0;
*(std::vector<char*> **)&baseptr = *(Derived **)&arg;
return baseptr;
}
int main()
{
Derived* d = new Derived();
void* upcast = foo(d);
void* upcast2 = foo2(d);
std::cerr << d << ", " << upcast << ", " << upcast2 << std::endl;
}
If you compile without -O2 the two values upcast and upcast2 are the
same, as they should be.
Using -O2 the results are different.
The bug occurrs with both:
g++ (GCC) 4.1.2 20070925 (Red Hat 4.1.2-27)
g++ (Ubuntu 4.4.1-4ubuntu9) 4.4.1
This kind of code is generated by SWIG for Java, so I can't change
the source.
Curiously the bug disappears if you put a print statement before the
assignment to baseptr.
--
Summary: optimizer dereference
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: attardi at di dot unipi dot it
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45246
