RFR (M): 8227434: G1 predictions may over/underflow with high variance input

[Thomas Schatzl]

Hi all,

   can I have reviews for this change that tries to fix possible 
underflows and overflows in our predictor use in case there is high 
variance input?

I did not analyze for every case whether the issue actually happened, 
but changed the get_new_prediction() calls to something I believe is 
appropriate for the given sequence. Cases where there has already been 
some clamping going on were obvious of course.

It's a bit boring to review...

CR:
https://bugs.openjdk.java.net/browse/JDK-8227434
Webrev:
http://cr.openjdk.java.net/~tschatzl/8227434/webrev/
Testing:
hs-tier1-5


Thanks,
   Thomas