RFR: 8344171: Clone and initialize Assertion Predicates in order instead of in reverse-order [v5]

[Emanuel Peter]

On Thu, 28 Nov 2024 08:56:53 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> This patch changes the order in which we clone and initialize Assertion Predicates from "reverse-order" to "in-order".
>> 
>> #### Current State: Mostly "reverse-order" for Assertion Predicates
>> We are currently cloning and initializing Assertion Predicates in reverse-order out of convenience and simplicity for most of the loop splitting optimizations - except for Loop Unswitching (see next section). This means that we do the following:
>> 
>>                                      old target loop entry
>>                                                |
>>          x                         Cloned Template Assertion
>>          |                                Predicate 2
>> Template Assertion                             |
>>     Predicate 1                       Initialized Assertion
>>          |               ==>               Predicate 2
>> Template Assertion                             |
>>     Predicate 2                    Cloned Template Assertion
>>          |                                Predicate 1
>>     source loop                                |
>>                                       Initialized Assertion
>>                                            Predicate 1
>>                                                |
>>                                           target loop
>> 
>> I don't think this is wrong but still kinda unexpected when trying to reason about a graph. But now with the recent refactorings, I think it's easy to change this to an in-order processing:
>> 
>>                                      old target loop entry
>>                                                |
>>          x                          Cloned Template Assertion
>>          |                                Predicate 1
>> Template Assertion                             |
>>     Predicate 1                       Initialized Assertion
>>          |               ==>               Predicate 1
>> Template Assertion                             |
>>     Predicate 2                     Cloned Template Assertion
>>          |                                Predicate 2
>>     source loop                                |
>>                                       Initialized Assertion
>>                                            Predicate 2
>>                                                |
>>                                           target loop
>> 
>>  This will also align all cloning/initializing of Assertion Predicates to the same order which was not the case before: Loop Unswitching already had an in...
>
> Christian Hagedorn has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Revert "8344035: Replace predicate walking code in Loop Unswitching with a predicate visitor"
>    
>    This reverts commit 550933659a8021131d9d1424fc6ff77b51745cbe.
>  - 8344035: Replace predicate walking code in Loop Unswitching with a predicate visitor

Marked as reviewed by epeter (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/22275#pullrequestreview-2467211464