RFR: 8344171: Clone and initialize Assertion Predicates in order instead of in reverse-order [v4]

[Christian Hagedorn]

On Thu, 28 Nov 2024 08:37:15 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 one additional commit since the last revision:
> 
>   Add some visualization

Thanks Emanuel!

I think I will wait until after the fork to integrate this since we are semantically changing the order which might have some unforeseeable side effects. I don't think this needs to go into JDK 24.

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PR Comment: https://git.openjdk.org/jdk/pull/22275#issuecomment-2505551385