RFR(S): 8237375: SimpleThresholdPolicy misses CounterDecay timestamp initialization

[Doerr, Martin]

Hi,

I'd like to fix warmup issues we observed in test compiler/c2/Test8004741.java.
The issue is a missing timestamp initialization which leads to a premature counter decay at the first safepoint with -XX:-TieredCompilation.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8237375

Webrev:
http://cr.openjdk.java.net/~mdoerr/8237375_CounterDecay/webrev.00/
The webrev applies on top of the preliminary fix for https://bugs.openjdk.java.net/browse/JDK-8235741.
I'll wait until that one gets pushed.

What it changes:

  *   Move class CounterDecay up
  *   Introduce reset_last_timestamp()
  *   Use this function in decay() and in SimpleCompPolicy::initialize()

Best regards,
Martin