Does gcc optimize "if (constant)" inside while loops?

[Andrew Haley]

Timur Tabi wrote:
> I have this code:
> 
> #define spin_event_timeout(condition, timeout, delay, rc)                   \
> {                                                                           \
> 	unsigned long __loops = tb_ticks_per_usec * timeout;                \
> 	unsigned long __start = get_tbl();                                  \
> 	while (!(rc = (condition)) && (tb_ticks_since(__start) <= __loops)) \
> 		if (delay)                                                  \
> 			udelay(delay);                                      \
> 		else	                                                    \
> 			cpu_relax();                                        \
> }
> 
> assuming that the 'delay' parameter is a constant, will gcc
> optimize-out the "if (delay)" when this macro is compiled?

Yes, because one of the arms of the conditional is trivially dead.

Andrew.