Citeren Dave Korn <[EMAIL PROTECTED]>:
On 23 April 2007 19:07, Diego Novillo wrote:
Mark Mitchell wrote on 04/23/07 13:56:
So, I think there's a middle ground between "exactly the same passes on
all targets" and "use Acovea for every CPU to pick what -O2 means".
Using Acovea to reveal some of the suprising, but beneficial results,
seems like a fine idea, though.
I'm hoping to hear something along those lines at the next GCC Summit. I
have heard of a bunch of work in academia doing extensive optimization
space searches looking for combinations of pass sequencing and
repetition to achieve optimal results.
My naive idea is for someone to test all these different combinations
and give us a set of -Ox recipes that we can use by default in the compiler.
Has any of the Acovea research demonstrated whether there actually is any
such thing as a "good default set of flags in all cases"? If the results
obtained diverge significantly according to the nature/coding
style/architecture/other uncontrolled variable factors of the application, we
may be labouring under a false premise wrt. the entire idea, mightn't we?
I don't think that has been shown. Acovea evaluation has only been
done on a few architectures, and I don't believe a comparison was made.
But, you guys are probably the best team to try that out: you have
access to a wide range of platforms, and the experience needed to
solve problems when they present them. Hopefully, my upcoming
framework will boost such an effort. Remember: adjusting the way in
which GCC handles -On flags is only needed if the tests suggest it
will be usefull.
greetings,
Kenneth
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