RFR: 8305637: Remove Opaque1 nodes for Parse Predicates and clean up useless predicate elimination [v2]

[Christian Hagedorn]

> This is the last clean-up PR before the complete fix for Assertion Predicates ([JDK-8288981](https://bugs.openjdk.org/browse/JDK-8288981)). 
> 
> This patch includes:
> - Removal of `ConI`->`Opaque1`->`Conv2B` input nodes for `ParsePredicateNodes` with the following additional changes:
>   - Adjusting `ParsePredicateNode` to block unwanted optimizations (added empty `ParsePredicateNode::Ideal()`).
>   - Changing `Compile::_parse_predicate_opaqs` to not store `Opaque1Nodes` to keep track of Parse Predicates but instead storing `ParsePredicateNodes` directly. Renamed to `Compile::_parse_predicates` and adjusted related methods.
>   - Removed asserts matching `Opaque1` -> `Conv2B` shape.
> - Cleaning up `eliminate_useless_predicates()`:
>   - Adjust code to find useful/useless Parse Predicates with the new `Compile::_parse_predicates` list with `ParsePredicateNodes` instead of `Opaque1Nodes`.
>   - Changing `ParsePredicateNode` to carry a `_useless` state which simplifies the elimination of useless predicates with `eliminate_useless_predicates()` and during IGVN (added `ParsePredicateNode::Value()` for that which also removes the predicate once we are in post loop opts IGVN). 
> - Some refactoring/clean-ups of involved code.
>   
> Testing: tier1-7 + some fuzzer testing
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:

  remove hash_delete()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15449/files
  - new: https://git.openjdk.org/jdk/pull/15449/files/d50356e1..763a6b4a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15449&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15449&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15449.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15449/head:pull/15449

PR: https://git.openjdk.org/jdk/pull/15449