[jdk17] RFR: 8268371: C2: assert(_gvn.type(obj)->higher_equal(tjp)) failed: cast_up is no longer needed [v2]

[Vladimir Ivanov]

> The way `CheckCastPP` nodes are handled now doesn't let redundant casts to be completely removed: even when the corresponding runtime check disappears, the cast node stays in the graph and it broadens/worsens the type of casted value.   
> 
> Proposed fix leaves `CheckCastPP` handling intact, but skips the insertion of redundant cast nodes as part of receiver subtype check. ​
> 
> Also, interface casts on receiver temporarily don't get a `CheckCastPP` irrespective of whether the subtype check is redundant or not. 
> 
> Though the assertion failures showed up after JDK-8267807, the bug was there long before. 
> 
> Testing: 
> - [x] hs-tier1 - hs-tier4

Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  Add -XX:+UnlockDiagnosticVMOptions

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

Changes:
  - all: https://git.openjdk.java.net/jdk17/pull/55/files
  - new: https://git.openjdk.java.net/jdk17/pull/55/files/156be6bd..9ffdcd9d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk17&pr=55&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk17&pr=55&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/55.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/55/head:pull/55

PR: https://git.openjdk.java.net/jdk17/pull/55