RFR: 8301630: C2: 8297933 broke type speculation in some cases [v2]

[Roland Westrelin]

> With 8297933, a TypeAryPtr is a lot more likely to have a null _klass
> and that breaks TypePtr::speculative_type().

Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:

  type system fix & test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12368/files
  - new: https://git.openjdk.org/jdk/pull/12368/files/266692b9..34c17a1d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12368&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12368&range=00-01

  Stats: 71 lines in 2 files changed: 70 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12368.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12368/head:pull/12368

PR: https://git.openjdk.org/jdk/pull/12368