This is AVR-GCC 4.8.1.
The problem: I have a state machien which looks like this:
void foo() {
some_setup;
while(1) {
switch(whatever) {
case (whatever): global_var = some_constant;
[ repeat 10 times ]
case (special): return;
}
}
}
The problem with this loop is that AVR has many registers. GCC thinks that
it will run sufficiently often that pre-seeding registers with all of these
"some_constant"s before entering the loop is a net win. Unfortunately that
is not true in my case; worse, the set-up takes *much* too long. Also, I'm
using -Os and this "optimization" definitely makes the code larger.
Is there a way to turn this type of optimization off? Moving the loop's guts
to a different function won't work because its innards depend on a couple of
variables created by "some_setup" which I don't want to pass as arguments
(besides, that'd be too slow). "while(__builtin_expect(1,0))" doesn't fix
the problem either.
--
-- Matthias Urlichs
