https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83468
Bug ID: 83468
Summary: -Wuninitialized warning not emitted when it should
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hannesroest at gmx dot ch
Target Milestone: ---
In the following code, gcc does not emit a warning / error even when compiled
with -Wuninitialized -Werror -Wmaybe-uninitialized :
#include <iostream>
class klass
{
public: void test2(double k) {std::cout << k << std::endl; k += 42; }
public: void test3(double& k) {k = 42;}
};
int main(int argc, const char** argv)
{
double q;
klass* ptr;
ptr = new klass();
ptr->test2(q);
ptr->test3(q);
ptr->test2(q);
}
where it should emit a warning about the line "ptr->test2(q);" where q is used
unitialized and even written to stdout. It clearly depends on two factors, ptr
being a pointer and the fact that test3 is getting called. Note that if the
line "ptr->test3(q);" is commented out or if an object instead of a pointer is
used, then gcc correctly emits a warning. Also if the line "ptr->test3(q);" is
replaced by "q = 42;" it will correctly emit a warning.
We ran into this issue in an automated test environment where the unitialized
value of the variable "q" then had the value of a specific memory location,
which made the error hard to track down and we expected "-Wuninitialized" to
catch this.
The issue is present in gcc 7.2 and current trunk. Clang correctly emits the
warning in the above code.
Also note that a slight variation of this will depend on the optimization
level:
#include <iostream>
class klass
{
public: void test(double& k) {k += 42;}
};
int main(int argc, const char** argv)
{
double q;
klass* ptr;
ptr = new klass();
q += 42;
ptr->test(q);
std::cout << q << std::endl;
}
will compile fine without optimization but will emit the warning with -O1, -O2,
-O3
