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

[Christian Hagedorn]

On Tue, 29 Aug 2023 08:39:39 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> 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()

I've pushed an update with the following changes:
- `is_uncommon_trap_if_pattern()` and `is_uncommon_trap_proj()`:
  - Changed `Deoptimization::Deopt_Reason` into a default argument for `is_uncommon_trap_if_pattern()` and `is_uncommon_trap_proj()` as most calls are only interested if the `If` just represents such a pattern. This allowed us to remove all the `Deoptimization::Reason_none` arguments in the calling code.
  - Changed them into `const` methods.
  - Removed/Moved Parse Predicate checking in `is_uncommon_trap_if_pattern()` as this should be the responsibility of the caller. The method simply wants to check if there is such a pattern with the given deopt reason.
- `create_new_if_for_predicate()`:
  - The continuation projection is always a Parse Predicate success projection (i.e. true projection). Changed types and variable names accordingly.
  - Other renaming and removing dead code.
- Changed some variable names to better highlight that where Parse Predicate success projections are passed around.

But I could also split these changes in a separate PR.

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PR Comment: https://git.openjdk.org/jdk/pull/15449#issuecomment-1700971776