Speed Impact experiment on GCJ

Wed Feb 15 10:38:00 GMT 2006

Hi Rui,
It would be of interest to know what JVM you're using for the non compiled case. Is it the 
gij interpreter or a Sun Java 1.5, or something else?
Regards,
Thomas Hallgren
Mark Wielaard wrote:
> Hi Rui,
>> On Wed, 2006年02月15日 at 01:41 +0000, Rui Wang wrote:
>> Having compiled the code with -O3 flag, it runs much faster compare to
>> previous one. Thanks. 
>> Great. Please do post the results so people can compare with the
> unoptimized version. It is interesting to see how different ways to
> compile a program impact the speed.
>>> However, I wonder why we need optimization to make native machine code
>> running faster than Java bytecode? In my experiment, the code is no
>> more complicated than a HelloWrold program. It has no features that
>> will mess things up like dynamic class loading. Therefore, the
>> translation from Java to native code should be straightforward,
>> isn't ? 
>> Without -O2 (or higher) the compiler tries to produce native code as
> fast as possible without even looking for some simple tricks to get fast
> code. It doesn't know this is just a very small program (you might link
> it with hundreds of files later) and it tries to get you code as soon as
> possible in the most naive way. If you tell it you want optimized code
> (-O2) it actually tries to give that to you, but it might take longer to
> generate it.
>> Cheers,
>> Mark