8325482: Test that distinct seeds produce distinct traces for compiler stress flags #26554

sarannat · 2025-07-30T13:38:37Z

Issue

The existing test (compiler/debug/TestStress.java) verifies that compiler stress options produce consistent traces when using the same seed. However, there is currently no test to ensure that different seeds result in different traces.

Solution

Added a test case to assess the distinctness of traces generated from different seeds. This fix addresses the fragility concern highlighted in JDK-8325482 by verifying that traces produced using N (in this case 10) distinct seeds are all not identical.

Changes to `compiler/debug/TestStress.java`

While investigating this issue, I observed that in compiler/debug/TestStress.java, the stress options for macro expansion and macro elimination were not being triggered because there were fewer than 2 macro nodes. Note that the shuffle_macro_nodes() in compile.cpp is only meaningful when there are more than two macro nodes. The generated traces for macro expansion and macro elimination in TestStress.java were empty. I have proposed changes to address this problem.

Progress

Change must be properly reviewed (1 review required, with at least 1 Reviewer)
Change must not contain extraneous whitespace
Commit message must refer to an issue

Issue

JDK-8325482: Test that distinct seeds produce distinct traces for compiler stress flags (Enhancement - P4)

Reviewers

Christian Hagedorn (@chhagedorn - Reviewer)
Damon Fenacci (@dafedafe - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/26554/head:pull/26554
$ git checkout pull/26554

Update a local copy of the PR:
$ git checkout pull/26554
$ git pull https://git.openjdk.org/jdk.git pull/26554/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 26554

View PR using the GUI difftool:
$ git pr show -t 26554

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/26554.diff

Using Webrev

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bridgekeeper · 2025-07-30T13:39:45Z

👋 Welcome back snatarajan! 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 · 2025-07-30T13:41:14Z

@sarannat 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:

8325482: Test that distinct seeds produce distinct traces for compiler stress flags

Reviewed-by: chagedorn, dfenacci

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 76 new commits pushed to the master branch:

67ba8b4: 8364514: [asan] runtime/jni/checked/TestCharArrayReleasing.java heap-buffer-overflow
febd4b2: 8360515: PROPERFMTARGS should always use size_t template specialization for unit
c0c7d39: 8364587: Update jpackage internal javadoc
... and 73 more: https://git.openjdk.org/jdk/compare/c8517356314c9dd1123401a21968009066053e5b...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.

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openjdk · 2025-07-30T13:42:21Z

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

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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 · 2025-07-31T07:22:20Z

Webrevs

chhagedorn

Thanks for adding such a test. A few comments, otherwise, it looks good!

chhagedorn · 2025-07-31T07:26:08Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+ * @requires vm.debug == true & vm.compiler2.enabled
+ * @requires vm.flagless


can be merged:

Suggested change

* @requires vm.debug == true & vm.compiler2.enabled

* @requires vm.flagless

* @requires vm.debug == true & vm.compiler2.enabled & vm.flagless

chhagedorn · 2025-07-31T07:26:16Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+ * @key stress randomness
+ * @requires vm.debug == true & vm.compiler2.enabled
+ * @requires vm.flagless
+ * @summary Tests that stress compilations with the N different seed yield different


Suggested change

* @summary Tests that stress compilations with the N different seed yield different

* @summary Tests that stress compilations with the N different seeds yield different

chhagedorn · 2025-07-31T07:32:28Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+                igvnTraceSet.add(igvnTrace(s));
+                ccpTraceSet.add(ccpTrace(s));
+                macroExpansionTraceSet.add(macroExpansionTrace(s));
+                macroEliminationTraceSet.add(macroEliminationTrace(s));


A suggestion, do you also want to check here that two runs with the same seed produce the same result to show that different seeds really produce different results due to the seed and not just some indeterminism with the test itself? How long does your test need now and afterwards with a fastdebug build? Maybe we can also lower the number of seeds if it takes too long or only do the equality-test for a single seed.

Thank you for the review.

This is a very good point. I implemented and tested what you suggested. Below are some numbers that I obtained from running the test compiler/debug/TestStressDistinctSeed.java with jtreg -vt

commit 513ab6d [with no check for same seed -> same trace ]
slowdebug
build: 7.205 seconds
driver: 32.111 seconds
fastdebug
build: 0.002 seconds
driver: 9.102 seconds

commit 7eff4d5 [with check for same seed -> same trace and N = 10 ]
slowdebug**
build: 7.55 seconds
driver: 63.108 seconds
fastdebug
build: 0.0 seconds
driver: 16.259 seconds

commit 14617e0 [with check for same seed -> same trace and N = 5 ]
slowdebug
build: 0.001 seconds
driver: 31.946 seconds
fastdebug
build: 0.0 seconds
driver: 8.596 seconds

I think N=5 for the updated test looks reasonable. Do you think this is okay ?

Thanks for the update and the numbers! I agree that N=5 seems reasonable. Looks good!

chhagedorn · 2025-08-04T06:18:21Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+                igvntrace = igvnTrace(s);
+                ccptrace = ccpTrace(s);
+                macroexpansiontrace = macroExpansionTrace(s);
+                macroeliminationtrace = macroEliminationTrace(s);


Nit: You should probably use camelCase for readability of the variables.

dafedafe

Thanks for looking into this @sarannat! I just left a couple of inline comments.

dafedafe · 2025-08-04T08:14:28Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+        String igvntrace, ccptrace, macroexpansiontrace, macroeliminationtrace;
+        if (args.length == 0) {
+            for (int s = 0; s < 5; s++) {
+                igvntrace = igvnTrace(s);


Did you choose the 0-4 seeds to be sure that there are at least a couple of different traces? I guess it wouldn't be so easy to exclude that with random values, right?

Thank you for the review.
This comes from compiler/debug/TestStress.java and my reasoning is same as what you mentioned above.

dafedafe · 2025-08-04T08:29:04Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+
+/*
+ * @test
+ * @key stress randomness


Is the test actually "randomised"?

My argument for this comes from JDK-8270156 where stress and random keywords were added to all JTreg tests which use StressGCM, StressLCM and/or StressIGVN. This was extended to StressCCP, StressMacroExpansion, and StressMacroElimination.

chhagedorn

Thanks for the update!

dafedafe · 2025-08-05T08:07:13Z

test/hotspot/jtreg/compiler/debug/TestStressDistinctSeed.java

+    static void sum(int n) {
+        int[] arr1 = new int[n];
+        for (int i = 0; i < n; i++) {
+            synchronized (TestStressDistinctSeed.class) {


Was the synchronisation added to create a more "interesting" trace (the tests seem to be running sequentially anyway)?

Testing the stress options for macro expansion and macro elimination requires at least two macro nodes; otherwise, an empty trace is produced. Synchronisation was added solely to increase the number of macro nodes.

dafedafe

Thanks for looking at this and for the clarifications @sarannat.
LGTM

sarannat · 2025-08-05T08:31:24Z

Thank you for the reviews. Please sponsor.

sarannat · 2025-08-05T08:32:29Z

/integrate

openjdk · 2025-08-05T08:33:38Z

@sarannat
Your change (at version bca4a0e) is now ready to be sponsored by a Committer.

dafedafe · 2025-08-05T08:38:23Z

/sponsor

openjdk · 2025-08-05T08:39:57Z

Going to push as commit d25b9be.
Since your change was applied there have been 76 commits pushed to the master branch:

67ba8b4: 8364514: [asan] runtime/jni/checked/TestCharArrayReleasing.java heap-buffer-overflow
febd4b2: 8360515: PROPERFMTARGS should always use size_t template specialization for unit
c0c7d39: 8364587: Update jpackage internal javadoc
... and 73 more: https://git.openjdk.org/jdk/compare/c8517356314c9dd1123401a21968009066053e5b...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-08-05T08:40:17Z

@dafedafe @sarannat Pushed as commit d25b9be.

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

Initial Fix

513ab6d

openjdk bot changed the title ~~JDK-8325482: Test that distinct seeds produce distinct traces for compiler stress flags~~ 8325482: Test that distinct seeds produce distinct traces for compiler stress flags Jul 30, 2025

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Jul 30, 2025

sarannat marked this pull request as ready for review July 31, 2025 07:17

openjdk bot added the rfr Pull request is ready for review label Jul 31, 2025

chhagedorn reviewed Jul 31, 2025

View reviewed changes

sarannat added 2 commits August 1, 2025 13:21

Adding test for same seed --> same result for N = 10

7eff4d5

changing N to 5

14617e0

chhagedorn approved these changes Aug 4, 2025

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Aug 4, 2025

dafedafe reviewed Aug 4, 2025

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addressing review comments on camelCase

bca4a0e

openjdk bot removed the ready Pull request is ready to be integrated label Aug 4, 2025

chhagedorn approved these changes Aug 5, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Aug 5, 2025

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		* @requires vm.debug == true & vm.compiler2.enabled
		* @requires vm.flagless

	* @summary Tests that stress compilations with the N different seed yield different
	* @summary Tests that stress compilations with the N different seeds yield different

8325482: Test that distinct seeds produce distinct traces for compiler stress flags #26554

8325482: Test that distinct seeds produce distinct traces for compiler stress flags #26554

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Issue

Solution

Changes to compiler/debug/TestStress.java

Progress

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