RFR (S): C1 still does eden allocations when TLAB is enabled

[JC Beyler]

Hi all,

(Not sure this is the right list, it's a C1 fix but regarding runtime
interactions...)

With Robbin Ehn, we had worked together on making TLAB and contiguous
inlining consistent in the interpreter across architectures. When testing
my heap monitoring system, it turned out that C1 is still being
inconsistent.

I'm not sure if we had left this case intentionally or not but, if we want
it all to be consistent, we should perhaps fix it.

I created this to track this:
https://bugs.openjdk.java.net/browse/JDK-8190862

I also created a fix to make it consistent:
http://cr.openjdk.java.net/~jcbeyler/8207252/webrev.00/

Basically, we say:
  - If TLAB is enabled, then go directly to the slow path in these cases
  - If TLAB is disabled, try inline contiguous allocations if possible

Let me know if you have any questions and if someone could review if we
agree to it, that would be great!

Thanks,
Jc