Re: Should -fcross-jumping be part of -O1?

[Scott Robert Ladd <coyote at coyotegulch dot com>]

Richard Kenner wrote:
>     Well as part of this thought experiment, please consider that if each
>     of these five axes has three settings, then there are 3**5
>     combinations, which is a large number, and of course there is no
>     possibility of the compiler behaving in 3**5 significantly different ways.
>
> Right now, I count about 20 different optimizations switches and
> 2**20 is significantly larger than 3**5!

And As I have pointed out in my Acovea article, my second-generation 
tests were performed with 64 different options, some of which had more 
than one state (e.g., finline-limit, -mfpmath). Even assuming a simple 
on/off setting and no changes in parameterized options (-finline-limit), 
that's 2**63, or 9,223,372,036,854,775,808 combinations.

Which is why I wrote Acovea in the first place. I'm refining and 
expanding the algorithm to search for code size and accuracy in addition 
to generated code speed; results are still computing. I suspect it is 
more likely to find a happy medium for general options than it is to 
define scaling for several optimization axes.

--
Scott Robert Ladd
Coyote Gulch Productions (http://www.coyotegulch.com)
Software Invention for High-Performance Computing