RFR: 8323220: Reassociate loop invariants involved in Cmps and Add/Subs [v12]

[Emanuel Peter]

On Thu, 21 Mar 2024 05:35:43 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 15 additional commits since the last revision:
> 
>  - Add tests for add/sub reassociation
>  - Merge branch 'master' into licm
>  - Make inputs deterministic. Make size an arg. Fix comments. Formatting.
>  - Update test to utilize @setup method for arguments
>  - Merge branch 'master' into licm
>  - Add correctness test for some random tests with random inputs
>  - Add some correctness tests where we do reassociate
>  - Remove unused TestInfo parameter. Have some tests exit mid-loop.
>  - Merge branch 'master' into licm
>  - Small fixes and add check methods for tests
>  - ... and 5 more: https://git.openjdk.org/jdk/compare/d6e69638...b151293d

Just two little details, then we should be ready!
Ping me once you updated it, and I will run our internal testing one more time before approving!

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateAddSub.java line 36:

> 34:  * @summary Test loop invariant code motion of add/sub through reassociation
> 35:  * @library /test/lib /
> 36:  * @run driver compiler.c2.loopopts.InvariantCodeMotionReassociateAddSub

Suggestion:

 * @run main compiler.c2.loopopts.InvariantCodeMotionReassociateAddSub

Otherwise external flags are not passed in.

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 36:

> 34:  * @summary Test loop invariant code motion for cmp nodes through reassociation
> 35:  * @library /test/lib /
> 36:  * @run driver compiler.c2.loopopts.InvariantCodeMotionReassociateCmp

Suggestion:

 * @run main compiler.c2.loopopts.InvariantCodeMotionReassociateCmp

Just like above

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17375#pullrequestreview-1951942814
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1533728671
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1533760799