8273277: C2: Move conditional negation into rc_predicate #5987

neliasso · 2021-10-18T13:24:19Z

Hi,

I need some feedback on this patch. This was reported from Tencent and found in internal testing about the same time. This patch is based on a a patch provided by Tencent.

In some very specific circumstances we need to negate the range checks that we create in PhaseIdealLoop::loop_predication_impl_helper. This is done in three places, but that method also calls insert_initial_skeleton_predicate where this isn't taken into account.

To simplify things I have moved the negation logic into rc_predicate. This should prevent us from missing this check again.

I do have a concern that negating the condition of the rangecheck in the skeleton predicate, since the skeleton predicate will be used as a clone template, and some rangechecks optimizations seems to assume that range checks always have LT as the condidtion. On the other hand - it is a really uncommon scenario since we haven't failed here before.

Feedback appreciated.

Best regards,
Nils

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JDK-8273277: C2: Move conditional negation into rc_predicate

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Tobias Hartmann (@TobiHartmann - Reviewer)
Christian Hagedorn (@chhagedorn - Reviewer)
Vladimir Kozlov (@vnkozlov - Reviewer)

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bridgekeeper · 2021-10-18T13:24:38Z

👋 Welcome back neliasso! 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 · 2021-10-18T13:27:00Z

@neliasso The following label will be automatically applied to this pull request:

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mlbridge · 2021-10-18T14:40:09Z

Webrevs

TobiHartmann

I do have a concern that negating the condition of the rangecheck in the skeleton predicate, since the skeleton predicate will be used as a clone template, and some rangechecks optimizations seems to assume that range checks always have LT as the condidtion. On the other hand - it is a really uncommon scenario since we haven't failed here before.

Is there any specific code that you worry about?

I think it should be fine because the purpose of copying and instantiating skeleton range check predicates is to guarantee that control/data paths die consistently when the main loop induction variable falls outside of the allowed range of an array access. But @rwestrel and @chhagedorn looked more into this recently.

Can we add the test that Tencent found as well?

Please update the affects versions in the bug report.

neliasso · 2021-11-09T20:27:55Z

I do have a concern that negating the condition of the rangecheck in the skeleton predicate, since the skeleton predicate will be used as a clone template, and some rangechecks optimizations seems to assume that range checks always have LT as the condition. On the other hand - it is a really uncommon scenario since we haven't failed here before.

Is there any specific code that you worry about?

I have seen checks for LT, but I see none that specifically would be affecting this change.

I think it should be fine because the purpose of copying and instantiating skeleton range check predicates is to guarantee that control/data paths die consistently when the main loop induction variable falls outside of the allowed range of an array access. But @rwestrel and @chhagedorn looked more into this recently.

Can we add the test that Tencent found as well?

Yes - I've added it.

Please update the affects versions in the bug report.

Done.

TobiHartmann

Looks good to me.

TobiHartmann · 2021-11-10T12:22:58Z

test/hotspot/jtreg/compiler/loopopts/TestSkeletonPredicateNegation.java

+ * @test
+ * @bug 8273277
+ * @summary Skeleton predicates sometimes need to be negated
+ * @run main compiler.loopopts.TestSkeletonPredicateNegation


I think this should be changed to @run driver.

TobiHartmann · 2021-11-10T12:23:54Z

test/hotspot/jtreg/compiler/loopopts/TestSkeletonPredicateNegation.java

+        }
+    }
+
+    public void mainTest (String[] args){


Code style should be mainTest(String[] args) {

openjdk · 2021-11-10T12:26:19Z

@neliasso 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:

8273277: C2: Move conditional negation into rc_predicate

Reviewed-by: thartmann, chagedorn, 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 341 new commits pushed to the master branch:

67c2714: 8276889: Improve compatibility discussion in instanceKlass.cpp
a5c160c: 8267108: Alternate Subject.getSubject and doAs APIs that do not depend on Security Manager APIs
ce3ed65: 8273154: Provide a JavadocTester method for non-overlapping, unordered output matching
f561d3c: 8276864: Update boot JDKs to 17.0.1 in GHA
38ec3a1: 8276672: Cannot build hsdis on WSL
55b36c6: 8276825: hotspot/runtime/SelectionResolution test errors
0f23c6a: 8276926: Use String.valueOf() when initializing File.separator and File.pathSeparator
a0b8445: 8276846: JDK-8273416 is incomplete for UseSSE=1
a3f710e: 8276215: Intrinsics matchers should handle native method flags better
0f463a7: 8276845: (fs) java/nio/file/spi/SetDefaultProvider.java fails on x86_32
... and 331 more: https://git.openjdk.java.net/jdk/compare/ebb1363e5d6b47daf1badad93490580fedcb0572...master

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chhagedorn

That looks reasonable to me.

vnkozlov

I agree.

neliasso · 2021-11-12T10:06:59Z

/integrate

openjdk · 2021-11-12T10:08:38Z

Going to push as commit 710f496.
Since your change was applied there have been 364 commits pushed to the master branch:

6b833db: 8275329: ZGC: vmTestbase/gc/gctests/SoftReference/soft004/soft004.java fails with assert(_phases->length() <= 1000) failed: Too many recored phases?
1e941de: 8275197: Remove unused fields in ThaiBuddhistChronology
6954b98: 8186670: Implement _onSpinWait() intrinsic for AArch64
3445e50: 8276265: jcmd man page is outdated
0ca0acf: 8276947: Clarify how DateTimeFormatterBuilder.appendFraction handles value ranges
b0d7a9d: 8276994: java/nio/channels/Channels/TransferTo.java leaves multi-GB files in /tmp
8aae88b: 8276763: java/nio/channels/SocketChannel/AdaptorStreams.java fails with "SocketTimeoutException: Read timed out"
6f35eed: 8079267: [TEST_BUG] Test java/awt/Frame/MiscUndecorated/RepaintTest.java fails
5e98f99: 8276800: Fix table headers in NumericShaper.html
2ca4ff8: 8244202: Implementation of JEP 418: Internet-Address Resolution SPI
... and 354 more: https://git.openjdk.java.net/jdk/compare/ebb1363e5d6b47daf1badad93490580fedcb0572...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-11-12T10:08:53Z

@neliasso Pushed as commit 710f496.

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

8273277 fix rc_predicate

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openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Oct 18, 2021

neliasso marked this pull request as ready for review October 18, 2021 14:36

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8273277: C2: Move conditional negation into rc_predicate #5987

8273277: C2: Move conditional negation into rc_predicate #5987

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8273277: C2: Move conditional negation into rc_predicate #5987

8273277: C2: Move conditional negation into rc_predicate #5987

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neliasso commented Oct 18, 2021 • edited by openjdk bot Loading

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