Wrong output for the initialization of static variables within a function

[Redstone1024]

For the initialization of static variables within functions, based on comparison with assembly output and analysis, I believe that a call to __cxa_atexit should be included, otherwise the class object cannot be destructured on program exit.

The following references are used in the analysis process.

C++ Insights

Compiler Explorer

This function call is missing.

mov     edx, OFFSET FLAT:__dso_handle
mov     esi, OFFSET FLAT:_ZZ11get_examplevE4temp
mov     edi, OFFSET FLAT:_ZN14example_structD1Ev
call    __cxa_atexit

Translated with DeepL.

[andreasfertig]

Hello @Redstone1024,

thanks for reporting this. As far as I can tell, you're right. The only thing is that __cxa_atexit requires parameters. C++ Insights doesn't show destructors as they are not part of the AST. I must figure out what I want to do in this special case. Of course, if you bring me a PR, I will most likely accept that :-)

Andreas

[Redstone1024]

Thanks for the reply, also if(!__tempGuard) should it be if((__tempGuard & 0xff) == 0) ? After all, here it should ensure that the initialization is complete, not continue the logic below while other threads are initializing.

Also __tempGuard = true; doesn't seem to be correct.

Here is the test code with what I think the output is.

struct example_struct
{
	example_struct() { throw; }
	~example_struct() { }
};

example_struct& get_example()
{
	static example_struct temp;
	return temp;
}

struct example_struct
{
	inline example_struct() { throw; }
	inline ~example_struct() noexcept { }
};

example_struct& get_example()
{
	static uint64_t __tempGuard;
	alignas(example_struct) static char __temp[sizeof(example_struct)];
	if((__tempGuard & 0xff) == 0)
	{
		if(__cxa_guard_acquire(&__tempGuard))
		{
			try
			{
				new (&__temp) example_struct();
			}
			catch(...)
			{
				__cxa_guard_abort(&__tempGuard);
				throw;
			}
			__cxa_guard_release(&__tempGuard);
			__cxa_atexit(example_struct::~example_struct, &__temp, &__dso_handle);
		}
	}
	return *reinterpret_cast<example_struct*>(__temp);
}

Thanks again.