为优化级别为 0 的 std::vector 调用两次析构函数

Question

I am trying to understand the assembly code generated for the std::vector and its emplace_back (or) push_back function using compiler explorer .

Note: Optimization level is 0 ie, -O0 is used

One thing that I couldn't understand is that why are there two destructors being called instead of one (As you can see only one vector is being created. If I assume that a temporary object is being created internally, then atlease I have to see a call to std::vector constructor.

This is same with clang compiler as well.

Can someone please explain what is happening here?

Edit 1:

#include <vector>
int main()
{
    std::vector<int> vec;
    vec.emplace_back(10);
}

Edit 2: Removed the screenshot as it is hard to read it.

Answer 1

There's a clue at line 34: call _Unwind_Resume . That block of code, from lines 28 through 34, is for stack unwinding when an exception is thrown. The normal code path goes through the destructor call at line 25, then, at line 27, jumps past the exception code, to line 35, and from there it returns from the function.

Just to clarify, there's magic here: the call to _Unwind_Resume does not return to the caller. It's a trick, to get the address of the block that was being executed, so that the exception handling code can figure out where it was and continue up the stack.