Can different optimization levels lead to functionally different code?

Question

I am curious about the liberties that a compiler has when optimizing. Let\'s limit this question to GCC and C/C++ (any version, any flavour of standard):

Is it possi

Answer 1

a.c:

char *f1(void) { return "hello"; }

b.c:

#include 

char *f1(void);

int main()
{
    if (f1() == "hello") printf("yes\n");
        else printf("no\n");
}

Output depends on whether merge string constants optimization is enabled or disabled:

$ gcc a.c b.c -o a -fno-merge-constants; ./a
no
$ gcc a.c b.c -o a -fmerge-constants; ./a
yes