On 31/10/2019 17:30, Segher Boessenkool wrote:
On Thu, Oct 31, 2019 at 09:10:34AM +0100, David Brown wrote:
I think there is a general attitude of "I'm compiling for a small
microcontroller with only 32 KB flash - so I must use flags to make the
code as small as possible". In fact, if you have 32 KB flash then you
need to make your code at most 32 KB in size - code of 31 KB is just as
good as code of 17 KB. As long as your code fits, any further reduction
in size is unnecessary.
Yeah, unless you're already at 31kB and now have to add a feature :-)
I haven't reported any "-O2 smaller than -Os" bugs, as far as I can
remember, but have merely noted it as a pattern that I see sometimes. I
will try to keep an eye out for when I see it again.
Thanks!
Do you have any reference for the heuristic parameters set by -Os ? (I
am perfectly happy with "it's in this file in the gcc source code", if
that is the answer.)
It's not just parameters, it's all over the code:
$ grep optimize_[a-z]*_for_ *.c | wc -l
219
$ grep -l optimize_[a-z]*_for_ *.c | wc -l
66
(and that does not include the target code -- there are about 300 more in
all targets combined).
Segher
And that's not to mention all the places like rtx_costs that turn that
into a local function argument with a different name - often something
like time_p, or size_p.
R.
