Combine four insns

[Steven Bosscher]

On Mon, Aug 9, 2010 at 4:34 PM, Toon Moene <toon@moene.org> wrote:
> Bernd Schmidt wrote:
>
>> On 08/07/2010 10:10 AM, Eric Botcazou wrote:
>
>>> Combining Steven and Bernd's figures, 1% of a bootstrap time is 37% of
>>> the combiner's time.  The result is 0.18% more combined insns.  It seems to
>>> me that we are already very far in the directory of diminishing returns.
>>
>> Better to look at actual code generation results IMO.  Do you have an
>> opinion on the examples I included with the patch?
>
> Well, one of the limitations of this analysis is that it is static - it
> doesn't say what the run-time influence of the simplification is.
>
> In case it is inside a heavily used loop, it might be far more important
> than it at first looks ...

With that argument alone, you can justify a superoptimizer at -O2 :-P

There has to be a trade-off at some point.

Ciao!
Steven