On Tue, May 13, 2008 at 9:13 PM, Nick Spence <nick.spence@xxxxxxxxxxxxx> wrote:
> addr = 0;
> for (i = 0; i < 16; i++) *(addr++) = 0;
My guess is that GCC knows that your program is invoking nasal demons
(undefined behaviour from dereferencing a null pointer) and you're
lucky it's even generating code for the second loop at all!
I got a conditional jump by replacing your initialization of addr with:
asm("" : "=g" (addr) : "0" (0));
That should make the NULL-ness of addr invisible to GCC. If you can
(and maybe your environment doesn't allow [much] initialized data),
you could also declare addr as a global variable initialized to zero.
Then hope that link-time optimization doesn't see through your
trickery again in a few months/years when it becomes mainstream!
