Re: Which optimization levels affect gimple?

["Paulo J. Matos" <pocm at soton dot ac dot uk>]

On 24 Jan 2007 09:56:55 -0800, Ian Lance Taylor <iant@google.com> wrote:
> "Paulo J. Matos" <pocm@soton.ac.uk> writes:
>
> > Which optimization levels affect gimple?
> > I've tried for a program to check what kind of gimple code you get
> > with -fdump-tree-gimple and -O0 and -O3 have different results,
> > however, -O3 and -O9 have exactly the same output. Will -Ox for x > 3,
> > generate the same gimple trees? (i.e., are done in backend of gcc?)
>
> At present, as far as I know, the highest defined optimization level
> is -O3.  -ONUMBER where NUMBER > 3 is equivalent to -O3.  There is no
> particular guarantee that will remain true in the future, although
> there are also no current plans to change it.

That's quite curious. I always thought that O3 was different to O4,
O5, ... O9. Still, beyond O3 optimizations were not safe... maybe an
old gcc myth! :-)

Thanks for clearing that up to me.

> Ian


--
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK