RFR: 8369258: C2: enable ReassociateInvariants for all loop types

[Emanuel Peter]

On Tue, 7 Oct 2025 07:36:41 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> Currently ReassociateInvariants is only enabled for int counted
> loops. I noticed, enabling it for long counted loops helps RCE. It
> also seems like something that would help any loop. I propose enabling
> it for all inner loops.

Nice. That looks reasonable. And great that it addresses my two reports!
I think you should now close my two reports as duplicates.

Once this is integrated, I'll do some investigations on `TestAliasingFuzzer.java`, to see if we might be able to enable some more IR rules there. If not, I'll file some more reports ;)

I'll run some internal testing now...

test/hotspot/jtreg/compiler/loopopts/TestReassociateInvariants.java line 28:

> 26:  * @summary
> 27:  * @library /test/lib /
> 28:  * @run driver compiler.loopopts.TestReassociateInvariants

I'm missing a `@bug 8369258`
Suggestion:

 * @test
 * @bug 8369258
 * @summary
 * @library /test/lib /
 * @run driver compiler.loopopts.TestReassociateInvariants

test/hotspot/jtreg/compiler/loopopts/superword/TestMemorySegment_8365982.java line 40:

> 38:  *          can also tighten up the IR rules there.
> 39:  * @library /test/lib /
> 40:  * @run driver compiler.loopopts.superword.TestMemorySegment_8365982

You should add the new bug-id to the one above! `@bug 8324751 8369258`

test/hotspot/jtreg/compiler/loopopts/superword/TestMemorySegment_8365982.java line 88:

> 86:     // does not have any range checks any more.
> 87:     // Now it vectorizes. That's good, but we should be able to vectorize without multiversioning.
> 88:     //

Can you please also remove the comments below?

test/hotspot/jtreg/compiler/loopopts/superword/TestMemorySegment_ReassociateInvariants1.java line 40:

> 38:  *          can also tighten up the IR rules there.
> 39:  * @library /test/lib /
> 40:  * @run driver compiler.loopopts.superword.TestMemorySegment_ReassociateInvariants1

You should add the new bug-id to the one above! `@bug 8324751 8369258`

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

PR Review: https://git.openjdk.org/jdk/pull/27666#pullrequestreview-3330405292
PR Review Comment: https://git.openjdk.org/jdk/pull/27666#discussion_r2425522357
PR Review Comment: https://git.openjdk.org/jdk/pull/27666#discussion_r2425516994
PR Review Comment: https://git.openjdk.org/jdk/pull/27666#discussion_r2425519554
PR Review Comment: https://git.openjdk.org/jdk/pull/27666#discussion_r2425515941