[MITgcm-devel] compiler optimization on SunOS

[Martin Losch]

I guess that depends on the compiler, right? the Sun Forte compiler  
has 5 optimization levels, this is the difference between 2 and 3
-O2  Do basic local and global optimization. This level
                usually gives minimum code size.

-O3  Adds global optimizations at the function level.
                In general, this level, and -O4, usually result in
                the minimum code size when used with the -xspace
                option.  Automatically turns on -depend data
                dependence analysis.

M.

On 18 Feb 2007, at 15:11, Dimitris Menemenlis wrote:

> Martin, et al., slightly off topic for this discussion, but I just  
> received following e-mail from NASA Ames, which indicates that -O3  
> may not always be faster than -O2 optimization.  D.
>
>> Hi Dimitris:
>> Best times at 1:20 (PBS wall clock time) are -O2 with both v10  
>> beta and
>> 9.1.039.
>> Second best time is 1:24 (PBS wall clock time) using -O3 and v10 beta
>> And in third and last place: 1:30 using -O3 and v9.1.039.
>> I'm going to ask Ken to do a -O2 timing with his version of the code.
>> I suppose we all assumed -O3 would be better and sometimes it just  
>> isn't.
>> I'll pluck out the exact times from the runs a bit later on.
>> Art
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