Confusing optimization

[Luca Béla Palkovics]

void a()
{
	... do my stuff
}

void b()
{
	... do my stuff
}

int main(int argc, char *argv[])
{
	a();
	b();	
}

>g++ main.cpp -O3
>./a.out
a takes 125ms
b takes 340ms

now the same but seperated
int main(int argc, char *argv[])
{
	a();
}

>g++ main.cpp -O3
>./a.out
a takes 85ms

Is this normal ? b has nothing todo with a .. why does a get slower ?
(b is also faster without a...)

Luca.