[EXP] New branch "exp" to perform some experiments for LWorld proprosal

[David Simms]

A new branch, called "exp" ("experiments"), has been created in the 
Valhalla project repository. There are a number of performance concerns 
raised when thinking about the current "LWorld prototype" [1], most 
notably the cost of:

  * differentiating various types of oops pointing to objects versus values
      o assumption is that klass indirection is too expensive
  * implementing alternative byte-code behavior, e.g.:
      o "ifacmp*", failed value oops ptr compare, is this test itself
        expensive, or implicit "equals" too expensive ?

The intention is to use the "exp" branch to conduct experiments on 
mainline JDK code, to investigate implementation costs and patterns in 
existing JDK and applications when considering "common cases" for 
compatibility and migration issues. Initial interest will be directed at 
JDK classes currently documented as "value-based" [2].

/D

[1] 
http://mail.openjdk.java.net/pipermail/valhalla-dev/2017-December/003631.html

[2] 
http://hg.openjdk.java.net/jdk/jdk/file/tip/src/java.base/share/classes/java/lang/doc-files/ValueBased.html