Optimization of conditional access to globals: thread-unsafe?

[David Miller]

From: Darryl Miles <darryl-mailinglists@netbauds.net>
Date: Mon, 29 Oct 2007 04:53:49 +0000

> What are the issues with "speculative loads" ?

The conditional might be protecting whether the pointer is valid and
can be dereferenced at all.

int *counter;

void foo(int counter_is_valid)
{
	if (counter_is_valid)
		(*counter)++;
}

And in another module that GCC can't see when compiling foo():

extern int *counter;

int main(void)
{
	int a = 0;

	foo(0);
	counter = &a;
	foo(1);

	return 0;
}