In GCC 10.2, -O2 optimization enables more than docs suggest

Jonathan Wakely
Wed Jan 20 19:44:11 GMT 2021

On Wed, 20 Jan 2021 at 19:06, mark_at_yahoo <> wrote:
> On 1/20/21 10:50 AM, Jonathan Wakely wrote:
> > That's a different situation though. With -O0 **NO** optimization is done,
> > at all. Any -f options for optimization passes are ignored entirely.
> >
> > The difference between -O1 and -O2 is the set of -f flags that differ, and
> > some specific checks for >= -O2. But the difference between -O0 and -O1 is
> > the difference between zero and non-zero. Completely off, or on.
> >
> That's interesting, Jonathan. You know far better than I do, and I
> haven't tried it in over a year (on an older version of GCC-ARM), but I
> swore the following did do something:

It might have done something, but it didn't optimize anything (and so
most of those options were ignored).

More information about the Gcc-help mailing list