RFR: 8275201: C2: hide klass() accessor from TypeOopPtr and typeKlassPtr subclasses [v2]

[Roland Westrelin]

> Outside the type system code itself, c2 usually assumes that a
> TypeOopPtr or a TypeKlassPtr's java type is fully represented by its
> klass(). To have proper support for interfaces, that can't be true as
> a type needs to be represented by an instance class and a set of
> interfaces. This patch hides the klass() accessor of
> TypeOopPtr/TypeKlassPtr and reworks c2 code that relies on it in a way
> that makes that code suitable for proper interface support in a
> subsequent change. This patch doesn't add proper interface support yet
> and is mostly refactoring. "Mostly" because there are cases where the
> previous logic would use a ciKlass but the new one works with a
> TypeKlassPtr/TypeInstPtr which carries the ciKlass and whether the
> klass is exact or not. That extra bit of information can sometimes
> help and so could result in slightly different decisions.
> 
> To remove the klass() accessors, the new logic either relies on:
> 
> - new methods of TypeKlassPtr/TypeInstPtr. For instance, instead of:
> toop->klass()->is_subtype_of(other_toop->klass())
> the new code is:
> toop->is_java_subtype_of(other_toop)
> 
> - variants of the klass() accessors for narrower cases like
>   TypeInstPtr::instance_klass() (returns _klass except if _klass is an
>   interface in which case it returns Object),
>   TypeOopPtr::unloaded_klass() (returns _klass but only when the klass
>   is unloaed), TypeOopPtr::exact_klass() (returns _klass but only when
>   the type is exact).
> 
> When I tested this patch, for most changes in this patch, I had the
> previous logic, the new logic and a check that verified that they
> return the same result. I ran as much testing as I could that way.

Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - review
 - Merge branch 'master' into JDK-8275201
 - Merge branch 'master' into JDK-8275201
 - build fix
 - Merge branch 'master' into JDK-8275201
 - whitespaces
 - remove klass accessor

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6717/files
  - new: https://git.openjdk.java.net/jdk/pull/6717/files/669421ca..98fcf8fb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6717&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6717&range=00-01

  Stats: 107606 lines in 2811 files changed: 74820 ins; 17905 del; 14881 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6717.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6717/head:pull/6717

PR: https://git.openjdk.java.net/jdk/pull/6717