8272573: Redundant unique_concrete_method_4 dependencies #5141

iwanowww · 2021-08-17T11:45:49Z

Equivalence checks in Dependencies::assert_common_4() are too strong which leads to unique_concrete_method_4 dependencies being repeatedly recorded and duplicating nmethod dependencies registered.

The underlying problem is note_dep_seen() mutates internal bitmap, but the nested checks fail fast.
So, multiple requests are required to populate the bit-map for all the arguments in order to make the detection of duplicate assertions work. And it leads to duplicate dependencies registered.

It turns out call_site_target_value is also affected in a similar manner (see Dependencies::assert_common_2 for dependencies without explicit context argument), so I fix it along the way.

Testing: hs-tier1 - hs-tier6

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Issue

JDK-8272573: Redundant unique_concrete_method_4 dependencies

Reviewers

Vladimir Kozlov (@vnkozlov - Reviewer)
Tobias Hartmann (@TobiHartmann - Reviewer)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/5141/head:pull/5141
$ git checkout pull/5141

Update a local copy of the PR:
$ git checkout pull/5141
$ git pull https://git.openjdk.java.net/jdk pull/5141/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 5141

View PR using the GUI difftool:
$ git pr show -t 5141

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/5141.diff

bridgekeeper · 2021-08-17T11:55:09Z

👋 Welcome back vlivanov! 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 · 2021-08-17T11:56:57Z

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

hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-08-17T18:40:38Z

Webrevs

01: Full - Incremental (b95f4003)
00: Full (3cdad37a)

vnkozlov · 2021-08-17T19:39:19Z

src/hotspot/share/code/dependencies.cpp

-    if (note_dep_seen(dept, x0) && note_dep_seen(dept, x1)) {
+    if (note_dep_seen(dept, x0)) {


Why x0 is special in all these cases?
Should we do || instead?

if (note_dep_seen(dept, x0) || note_dep_seen(dept, x1)) {

It's just a fast path approximate check which guards linear search over recorded dependencies.
note_dep_seen(dept, x0) == false says that such a dependency argument hasn't been seen before, but note_dep_seen(dept, x0) == true requires a search over recorded dependencies to prove the argument is in the right position.

Another way to fix it is to perform all the queries beforehand:

bool dep_seen_x0 = note_dep_seen(dept, x0); bool dep_seen_x1 = note_dep_seen(dept, x1); if (dep_seen_x0 && dep_seen_x1) { ... }

It should dramatically reduce the rate of false positives.

Pushed the implementation which checks all the arguments. Let me know what you prefer.

vnkozlov

Yes, I like it.

openjdk · 2021-08-17T22:13:47Z

@iwanowww 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:

8272573: Redundant unique_concrete_method_4 dependencies

Reviewed-by: kvn, thartmann

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 12 new commits pushed to the master branch:

5189047: 8272558: IR Test Framework README misses some flags
ec63957: 8272398: Update DockerTestUtils.buildJdkDockerImage()
14623cd: 8270835: regression after JDK-8261006
fe72197: 8272551: mark hotspot runtime/modules tests which ignore external VM flags
05d64da: 8272291: mark hotspot runtime/logging tests which ignore external VM flags
a68b5b9: 8272369: java/io/File/GetXSpace.java failed with "RuntimeException: java.nio.file.NoSuchFileException: /run/user/0"
a199ebc: 8272581: sun/security/pkcs11/Provider/MultipleLogins.sh fails after JDK-8266182
1cbf41a: 8225083: Remove Google certificate that is expiring in December 2021
cf64c3e: 8272326: java/util/Random/RandomTestMoments.java had two Gaussian fails
2ed7b70: 8272521: Remove unused PSPromotionManager::_claimed_stack_breadth
... and 2 more: https://git.openjdk.java.net/jdk/compare/0e3fde6c3c2f5c05777b79ff5eb1188014269b0f...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.

vnkozlov · 2021-08-17T22:24:14Z

On second thought, I don't get how it fixes the issue. Can you explain why it reduce false positive?
The only difference from original code is that you always run note_dep_seen(dept, x1).

TobiHartmann

Good catch! Looks good to me.

iwanowww · 2021-08-18T10:24:49Z

On second thought, I don't get how it fixes the issue. Can you explain why it reduce false positive?
The only difference from original code is that you always run note_dep_seen(dept, x1).

Yes, and that's the crucial difference which fixes the problem. The bug stems from the peculiarities of note_dep_seen() implementation.

Consider the original code:

if (note_dep_seen(dept, x0) && note_dep_seen(dept, x1)) {

When a fresh assertion is added, it records only x0 because note_dep_seen(dept, x0) == false and the check fails fast.
Next time the very same assertion is made, note_dep_seen(dept, x0) == true (because note_dep_seen() recorded x0, but x1 hasn't been checked before and note_dep_seen(dept, x1) == false. So, a duplicate dependency is recorded.

Unconditionally running note_dep_seen() on x0 and x1 lets note_dep_seen() observe both arguments on the first occurrence.

Can you explain why it reduce false positive?

Checking both arguments filters out cases when second argument differs thus reducing the chances linear scan is performed.

vnkozlov · 2021-08-18T16:06:23Z

Perfect! Thank you for explanation.

iwanowww · 2021-08-18T16:44:09Z

Thanks for the reviews, Vladimir and Tobias.

/integrate

openjdk · 2021-08-18T16:45:37Z

Going to push as commit 96107e3.
Since your change was applied there have been 17 commits pushed to the master branch:

4d6593c: 8272124: Cgroup v1 initialization causes NullPointerException when cgroup path contains colon
30b0f82: 8272626: Avoid C-style array declarations in java.*
e8f1219: 8271276: C2: Wrong JVM state used for receiver null check
79a06df: 8272567: [IR Framework] Make AbstractInfo.getRandom() static
481c1f0: 8269951: [macos] Focus not painted in JButton when setBorderPainted(false) is invoked
5189047: 8272558: IR Test Framework README misses some flags
ec63957: 8272398: Update DockerTestUtils.buildJdkDockerImage()
14623cd: 8270835: regression after JDK-8261006
fe72197: 8272551: mark hotspot runtime/modules tests which ignore external VM flags
05d64da: 8272291: mark hotspot runtime/logging tests which ignore external VM flags
... and 7 more: https://git.openjdk.java.net/jdk/compare/0e3fde6c3c2f5c05777b79ff5eb1188014269b0f...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-08-18T16:45:47Z

@iwanowww Pushed as commit 96107e3.

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

8272573: Redundant unique_concrete_method_4 dependencies

0544d99

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Aug 17, 2021

Handle all note_dep_seen cases

3cdad37

iwanowww marked this pull request as ready for review August 17, 2021 18:35

openjdk bot added the rfr Pull request is ready for review label Aug 17, 2021

vnkozlov reviewed Aug 17, 2021

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Check all arguments

b95f400

vnkozlov approved these changes Aug 17, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Aug 17, 2021

TobiHartmann approved these changes Aug 18, 2021

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openjdk bot closed this Aug 18, 2021

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		if (note_dep_seen(dept, x0) && note_dep_seen(dept, x1)) {
		if (note_dep_seen(dept, x0)) {

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