RFR: 8323220: Reassociate loop invariants involved in Cmps and Add/Subs [v15]

[Christian Hagedorn]

On Fri, 5 Apr 2024 17:36:46 GMT, Joshua Cao <duke at openjdk.org> wrote:

>> // inv1 == (x + inv2) => ( inv1 - inv2 ) == x
>> // inv1 == (x - inv2) => ( inv1 + inv2 ) == x
>> // inv1 == (inv2 - x) => (-inv1 + inv2 ) == x
>> 
>> 
>> For example,
>> 
>> 
>> fn(inv1, inv2)
>>   while(...)
>>       x = foobar()
>>       if inv1 == x + inv2
>>            blackhole()
>> 
>> 
>> We can transform this into
>> 
>> 
>> fn(inv1, inv2)
>>   t = inv1 - inv2
>>   while(...)
>>       x = foobar()
>>       if t == x
>>            blackhole()
>> 
>> 
>> Here is an example: https://github.com/openjdk/jdk/blob/b78896b9aafcb15f453eaed6e154a5461581407b/src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java#L910. LHS `1` and RHS `pos` are both loop invariant
>> 
>> Passes tier1 locally on Linux machine. Passes GHA on my fork.
>
> Joshua Cao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 24 additional commits since the last revision:
> 
>  - Fix typo
>  - Formatting, use @run driver, remove legacy header comments
>  - Merge remote-tracking branch 'josh/licm' into licm
>  - Merge branch 'master' into licm
>  - @run driver -> @run main
>  - Add tests for add/sub reassociation
>  - Merge branch 'master' into licm
>  - Merge branch 'master' into licm
>  - Merge branch 'master' into licm
>  - Merge branch 'master' into licm
>  - ... and 14 more: https://git.openjdk.org/jdk/compare/7ab2c08f...1b27aae4

Thanks for making the changes. One more minor thing, otherwise, looks good!

src/hotspot/share/opto/loopTransform.cpp line 277:

> 275:   }
> 276:   for (DUIterator i = n->outs(); n->has_out(i); i++) {
> 277:     BoolNode *bool_out = n->out(i)->isa_Bool();

Suggestion:

    BoolNode* bool_out = n->out(i)->isa_Bool();

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

Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17375#pullrequestreview-1985540351
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1555286670