On Thu, Apr 12, 2012 at 10:43 AM, Pedro Alves <pal...@redhat.com> wrote:
> On 04/12/2012 04:23 PM, Gabriel Dos Reis wrote:
>
>> because -Os says it optimizes for size, the expectation is clear.
>> -O3 does not necessarily give better optimization than -O2.
>
>
> No, but it does mean that GCC turns on more optimization options.
>
> "Optimize yet more. -O3 turns on all optimizations specified by -O2 and also 
> turns on the -finline-functions,
> -funswitch-loops, -fpredictive-commoning, -fgcse-after-reload, 
> -ftree-vectorize and -fipa-cp-clone options. "

I think we have perverted the meaning of "optimize yet more", and optimize
yet more does not yield better/faster code :-)
Yes, I understand the transformations; that does not justify for the awkward
user-interface.

>
> Just like -W3 wouldn't necessarily generate more warnings on
> your code than -W1, perhaps because your code is
> already "clean" enough.  It would simply be documented as:
>
> "-W3: Warn yet more.  -W3 turns on all warnings specified by -W2 and also 
> ...".
>
> I'll also note the parallel with -glevel, not just -O.
>
> So, 'gcc -glevel -Wlevel -Olevel' feels quite natural to me.
>
> --
> Pedro Alves

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