[Bug c++/103843] Direct call to Desctructor is optimized out

[georgii.shagov@be-tse.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103843

Georgii.Shagov <georgii.shagov@be-tse.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |FIXED

--- Comment #5 from Georgii.Shagov <georgii.shagov@be-tse.de> ---

> No, the destructor is not just a function in C++, it terminates the object
> being alive (not de-allocated though). You can then reuse the space for
> another object, either the same type or a different type by using the
> inplacement new.
> 
> > Why the content of the class had been re-initialized?
> 
> It was not re-initialized rather the store was removed.
> 
> > IMU: there should be not such obvious difference between optimized and
> > non-optimized code
> 
> why not, it is undefined code.

I really appreciate and value your Reply, Andrew.

I have modified the code a little bit:

#include <iostream>

class S {
public:
   S() = default;
   ~S() { i=10; }
   void foo() { this->~S(); }
   int getI() const { return i; }
private:
   int i{100};
};

int main()
{
   S s;
   do {
      std::cout << "Before foo: " << s.getI();
      s.foo();
      std::cout << "; After: " << s.getI() << std::endl;
   } while (false);
   return 0;
}

$g++ -O3 ./d.cpp 
$./a.out 
Before foo: 100; After: 0
$g++ -O0 ./d.cpp 
$./a.out 
Before foo: 100; After: 10

> No, the destructor is not just a function in C++, it terminates the object
> being alive (not de-allocated though). 

I do understand your point, yet I would not feel comfortable in sharing one.

- It is not clear: what function/code has reset S::i value to 0 after a Direct
call to Destructor?
- Why 0? :-?
- In order to avoid misleading I have allocated the object on the stack as you
can see. So, no-memory mgmt is not involved
- Does it mean gcc implants some code, being called after Destructor call,
resetting the content of the class Instance to 0? ::memset??
- Is there any agreement unto this? I would be happy to learn more about this.


Thnx in advance,
Yours truly, George