[8] RFR (XS): 8031695: CHA ignores default methods during analysis leading to incorrect code generation

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8031695/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8031695

CHA erroneously ignores default methods when looking for different 
versions of a method in a class hierarchy.

Consider the following hierarchy:
   interface I { default void m() { ... }}
   class A implements I {}

   class C extends A { }
   class D extends A { public void m() { ... } }

Call site: invokevirtual A.m()

A.m resolves to I.m. Searching from A, CHA finds only D.m and concludes 
that D.m is the only implementation of I.m, since 
Dependencies::is_concrete_method returns false for I.m.

But there is C with default implementation from I. So, if VM inlines D.m 
and then C's instance is passed as objectref, the wrong method is 
invoked (D.m instead of I.m).

The fix is to take default methods into account doing CHA analysis and 
treat the call site as non-monomorphic when a concrete method is found 
for a default method.

Conservative approach is chosen, since the fix is targeted for 8.

Testing: failing application, regression test, vm.defmeth.testlist, JDK 
regression tests (java/util/, java/lang)

Thanks!

Best regards,
Vladimir Ivanov