On Thu, Oct 04, 2012 at 07:08:02PM +0200, Richard Guenther wrote:
> But isn't it a fact that it _cannot_ modify init_count? If the second call
> is CSEable then it cannot have side-effects that are observable at
> the call site. Is the following an example you would consider to fall
> under your CSEing?
>
> int init_count;
> int data;
> int initialized;
>
> void init()
> {
> if (!initialized)
> {
> data = ++init_count;
> initialized = 1;
> }
> }
>
> inline int *get_me() __attribute ((pure));
> inline int *get_me()
> {
> init ();
> return &data;
> }
>
> int sink;
>
> int main()
> {
> sink = init_count;
> int *p = get_me();
> if (init_count != 1)
> __builtin_abort();
> initialized = 0;
> int *q = get_me();
> if (init_count != 2)
> __builtin_abort();
> return *p + *q;
> }
The above isn't a singleton function, as you are clearing initialized,
therefore it doesn't have the properties the thread_local var get_address
wrapper has. The singleton function really is
void singleton (void)
{
static __thread bool initialized;
if (!initialized) {
initialized = true;
call_some_function_that_may_modify_memory ();
}
}
and has side effects just first time in a thread.
Jakub
