Re: Java ready for number crunching?
On Fri, 23 May 2008, Mark Thornton wrote:
Lew wrote:
Mark Thornton wrote:
As far as I can see, with the current language specification, HotSpot
can't safely do this type of optimisation.
If Java were limited to static analysis your objections would carry more
weight.
From John Rose (in a comment at
http://blogs.sun.com/jrose/entry/fixnums_in_the_vm)
"The key question is always the deoptimization cost. In this case, it
looks like a full GC could be required to reformat the affected
object(s). It's the Smalltalk "become" primitive, the nasty version
which can change an object's size and layout. I don't think I'm brave
enough to make these transformations automagically. Maybe they would be
justified in the presence of assurances from the user."
Bingo.
You might also look at the comment from Howard Lovatt to the same blog
entry. That refers to the language changes necessary to allow such
optimisations without any fear of having to later deoptimize them.
You mean the link to:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4617197
? He covers all the important things, but also a lot of crazy ideas.
tom
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