8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort #17190

D-D-H · 2023-12-25T15:34:55Z

A minor improvement could be made for bubble sort in SuperWord::packset_sort to reduce the comparison count in bad cases.

See https://en.wikipedia.org/wiki/Bubble_sort

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Issue

JDK-8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort (Enhancement - P5)

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Emanuel Peter (@eme64 - Reviewer) ⚠️ Review applies to ba53ed56
Vladimir Kozlov (@vnkozlov - Reviewer)

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…kset_sort

bridgekeeper · 2023-12-25T15:36:25Z

👋 Welcome back ddong! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2023-12-25T15:38:10Z

@D-D-H The following label will be automatically applied to this pull request:

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mlbridge · 2023-12-25T15:40:53Z

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eme64 · 2024-01-04T12:36:01Z

@D-D-H can you explain what this improves?

Ah, I think I see now. You want to decrease n quicker, by determining the highest index at which a swap took place.
First I would suggest that you rename newN -> max_swap_index.

And a more fundamental question:
Why do we need this improvement? Do you see any timing bottleneck and improvement? And what is faster: bubbling up or down?

And do you know why we sort at all in extend_packlist and why we do it again and again?

D-D-H · 2024-01-04T15:51:27Z

And a more fundamental question: Why do we need this improvement? Do you see any timing bottleneck and improvement? And what is faster: bubbling up or down?

And do you know why we sort at all in extend_packlist and why we do it again and again?

Sorry, I don't know the theory or implementation of superword. (I hope to grasp it someday...)

I just found it when browsing the code. This change is trivial; if you think it's unnecessary, I'm fine with closing it.

eme64 · 2024-01-05T08:22:23Z

Ok. This change is fine with me. Thanks for taking the time to look into this :)

I was just curious what was your motivation. I may completely redo this code once I remove the alignment constraints (here used for sorting), but that will have to be decided in a few months.

Please do the renaming, and then I can run testing and give you my approval.

D-D-H · 2024-01-05T08:54:36Z

Please do the renaming, and then I can run testing and give you my approval.

Updated. Thanks.

eme64 · 2024-01-05T10:14:08Z

@D-D-H nice. Testing running.

eme64

@D-D-H testing passed. Looks good. Thanks for the change!

openjdk · 2024-01-08T08:47:05Z

@D-D-H This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort

Reviewed-by: epeter, kvn

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 212 new commits pushed to the master branch:

525063b: 8322878: Including sealing information Class.toGenericString()
c1282b5: 8323540: assert((!((((method)->is_trace_flag_set(((1 << 4) << 8))))))) failed: invariant
5ba69e1: 8322477: order of subclasses in the permits clause can differ between compilations
c96cbe4: 8313083: Print 'rss' and 'cache' as part of the container information
a7db4fe: 8323428: Shenandoah: Unused memory in regions compacted during a full GC should be mangled
b86c3b7: 8309218: java/util/concurrent/locks/Lock/OOMEInAQS.java still times out with ZGC, Generational ZGC, and SerialGC
475306b: 7057369: (fs spec) FileStore getUsableSpace and getUnallocatedSpace could be clearer
f016934: 8323518: Parallel: Remove unused methods in psParallelCompact.hpp
2174f66: 8323005: Parallel: Refactor PSPromotionManager::claim_or_forward_depth
1617067: 8323331: fix typo hpage_pdm_size
... and 202 more: https://git.openjdk.org/jdk/compare/6dfb8120c270a76fcba5a5c3c9ad91da3282d5fa...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

D-D-H · 2024-01-08T09:20:58Z

@eme64
Thank you! Do I need a second review?

eme64 · 2024-01-08T09:21:56Z

Yes, I think that would be preferrable, even though this is not a very complicated fix.

D-D-H · 2024-01-08T09:37:19Z

Yes, I think that would be preferrable, even though this is not a very complicated fix.

Okay. Thanks.

vnkozlov

Clever.

vnkozlov · 2024-01-08T20:59:53Z

src/hotspot/share/opto/superword.cpp

@@ -3526,12 +3526,11 @@ void SuperWord::packset_sort(int n) {
        Node_List* t = q_i;


Why you need this local t?

Good catch. Deleted.

vnkozlov · 2024-01-08T21:05:03Z

src/hotspot/share/opto/superword.cpp

@@ -3526,12 +3526,11 @@ void SuperWord::packset_sort(int n) {
        Node_List* t = q_i;
        *(_packset.adr_at(i)) = q_low;
        *(_packset.adr_at(i-1)) = q_i;
-        swapped = true;
+        max_swap_index = i;


So we not using i+1 here because all previous values should be < than i's
Right?

Yes.
The last i's value is > previous values and values between i and end are already sorted.

vnkozlov

Good.

D-D-H · 2024-01-12T15:19:43Z

/integrate

Thanks for the review.

openjdk · 2024-01-12T15:21:41Z

Going to push as commit c5e7245.
Since your change was applied there have been 247 commits pushed to the master branch:

65a0672: 8319773: Avoid inflating monitors when installing hash codes for LM_LIGHTWEIGHT
e22ab10: 8322537: Parallel: Remove experimental adjustment in PSAdaptiveSizePolicy
be900f1: 8323425: JFR: Auto-generated filename doesn't work with time-limited recording
68c4286: 8323008: filter out harmful -std* flags added by autoconf from CXX
7dc9dd6: 8234502: Merge GenCollectedHeap and SerialHeap
ed18222: 8323190: Segfault during deoptimization of C2-compiled code
3e19bf8: 8323529: Relativize test image dependencies in microbenchmarks
ba23025: 8322957: Generational ZGC: Relocation selection must join the STS
7c3a39f: 8323297: Fix incorrect placement of precompiled.hpp include lines
e72723d: 8323296: java/lang/Thread/virtual/stress/GetStackTraceALotWhenPinned.java#id1 timed out
... and 237 more: https://git.openjdk.org/jdk/compare/6dfb8120c270a76fcba5a5c3c9ad91da3282d5fa...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-01-12T15:21:49Z

@D-D-H Pushed as commit c5e7245.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8322735: C2: minor improvements of bubble sort used in SuperWord::pac…

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openjdk bot added the rfr Pull request is ready for review label Dec 25, 2023

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Dec 25, 2023

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vnkozlov approved these changes Jan 10, 2024

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8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort #17190

8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort #17190

D-D-H commented Dec 25, 2023 •

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		@@ -3526,12 +3526,11 @@ void SuperWord::packset_sort(int n) {
		Node_List* t = q_i;

8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort #17190

8322735: C2: minor improvements of bubble sort used in SuperWord::packset_sort #17190

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D-D-H commented Dec 25, 2023 • edited by openjdk bot Loading

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