Currently if you ask gcc -O2 (tried on 3.0) to evaluate
!a
it will give you code of the form:
cmp r4, #0
movne ip, #0
moveq ip, #1
how does one teach the optimiser that this is equivalent and 33% faster:
rsbs ip, r4, #1
movls ip, #0
(I've checked this with a loop
int value = 0;
while (--value) {
...
}
and it gives !a for all values of a)
Maybe I'm over-optimistic, but I would hope that the aggregate effect of small
gains where possible on common C operators would start to add up to slight
speed gains.
Nicholas Clark
--
Even better than the real thing: http://nms-cgi.sourceforge.net/