8356281: Fix for TestFPComparison failure due to incorrect result #25101

vamsi-parasa · 2025-05-07T16:05:53Z

This PR fixes the cause of failure in TestFPComparison while using APX NDD instructions.

The test passes after using this fix as shown below:

Passed: compiler/c2/irTests/TestFPComparison.java
Test results: passed: 1

==============================
Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR  SKIP   
   jtreg:test/hotspot/jtreg/compiler/c2/irTests/TestFPComparison.java
                                                         1     1     0     0     0   
==============================
TEST SUCCESS

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Issue

JDK-8356281: Fix for TestFPComparison failure due to incorrect result (Bug - P2)

Reviewers

Sandhya Viswanathan (@sviswa7 - Reviewer)
Tobias Hartmann (@TobiHartmann - Reviewer)
Jatin Bhateja (@jatin-bhateja - Reviewer)

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$ git checkout pull/25101

Update a local copy of the PR:
$ git checkout pull/25101
$ git pull https://git.openjdk.org/jdk.git pull/25101/head

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$ git pr checkout 25101

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https://git.openjdk.org/jdk/pull/25101.diff

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bridgekeeper · 2025-05-07T16:06:39Z

👋 Welcome back sparasa! 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 · 2025-05-07T16:07:50Z

@vamsi-parasa 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:

8356281: Fix for TestFPComparison failure due to incorrect result

Reviewed-by: sviswanathan, thartmann, jbhateja

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 133 new commits pushed to the master branch:

1afd887: 8356102: TestJcmdOutput, JcmdWithNMTDisabled and DumpSharedDictionary hs/tier1 tests fail on static-jdk
97b0dd2: 8336906: C2: assert(bb->is_reachable()) failed: getting result from unreachable basicblock
a989245: 8327466: ct.sym zip not reproducible across build environment timezones
... and 130 more: https://git.openjdk.org/jdk/compare/90f0f1b88badbf1f72d7b9434621457aa47cde30...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@sviswa7, @TobiHartmann, @jatin-bhateja) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

openjdk · 2025-05-07T16:09:11Z

@vamsi-parasa 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 · 2025-05-07T16:12:46Z

Webrevs

sviswa7 · 2025-05-08T00:16:24Z

cmovP_regUCF_ndd instruct doesn't have UseAPX as predicate.

merykitty · 2025-05-08T16:54:10Z

src/hotspot/cpu/x86/x86_64.ad

  ins_cost(200);
  format %{ "ecmovpl  $dst, $src1, $src2\n\t"
-            "ecmovnel $dst, $src1, $src2" %}
+            "cmovnel  $dst, $src2" %}


You need effect(TEMP dst) for these nodes, too.

Thank you! Please see the effect(TEMP dst) added for all the match rules.

vamsi-parasa · 2025-05-08T19:40:02Z

cmovP_regUCF_ndd instruct doesn't have UseAPX as predicate.

Please see the missing predicates added in the updated code.

sviswa7

Looks good to me.

TobiHartmann

Looks good to me. Testing on our side passed.

jatin-bhateja

Fix looks good to me.

jatin-bhateja · 2025-05-14T11:33:42Z

src/hotspot/cpu/x86/x86_64.ad

  ins_encode %{
    __ ecmovq(Assembler::parity, $dst$$Register, $src1$$Register, $src2$$Register);
-    __ ecmovq(Assembler::notEqual, $dst$$Register, $src1$$Register, $src2$$Register);
+    __ cmovq(Assembler::notEqual, $dst$$Register, $src2$$Register);


FTR,
Instruction sequence for NaN-APX:-

CMOVE DST , SRC if FLAG is PF
CMOVE DST , SRC if FLAG is NE

With APX

CMOVE DST, DEF_DST, SRC if FLAG is PF
CMOVE DST, DEF_DST, SRC if FLAT is NE

Root cause:
So in back-to-back CMOVEs we end up updating the DST with DEF_DST if ZF is set since NE is false and not retain the DST value updated by prior CMOVE, this is not the case with Non-APX case since second DST is not executed is ZF is set and DST retains the value set by prior CMOVE.

vamsi-parasa · 2025-05-14T15:29:38Z

Looks good to me. Testing on our side passed.

Thank you, Tobias!

vamsi-parasa · 2025-05-14T15:30:20Z

/integrate

vamsi-parasa · 2025-05-14T15:30:39Z

Fix looks good to me.

Thanks Jatin!

openjdk · 2025-05-14T15:31:25Z

@vamsi-parasa
Your change (at version 3fb569c) is now ready to be sponsored by a Committer.

sviswa7 · 2025-05-14T15:38:27Z

/sponsor

openjdk · 2025-05-14T15:39:12Z

Going to push as commit 10436c1.
Since your change was applied there have been 133 commits pushed to the master branch:

1afd887: 8356102: TestJcmdOutput, JcmdWithNMTDisabled and DumpSharedDictionary hs/tier1 tests fail on static-jdk
97b0dd2: 8336906: C2: assert(bb->is_reachable()) failed: getting result from unreachable basicblock
a989245: 8327466: ct.sym zip not reproducible across build environment timezones
... and 130 more: https://git.openjdk.org/jdk/compare/90f0f1b88badbf1f72d7b9434621457aa47cde30...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-05-14T15:39:23Z

@sviswa7 @vamsi-parasa Pushed as commit 10436c1.

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

JDK-8356281: Fix for TestFPComparison failure due to incorrect result

f2588f6

openjdk bot changed the title ~~JDK-8356281: Fix for TestFPComparison failure due to incorrect result~~ 8356281: Fix for TestFPComparison failure due to incorrect result May 7, 2025

openjdk bot added the rfr Pull request is ready for review label May 7, 2025

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label May 7, 2025

merykitty reviewed May 8, 2025

View reviewed changes

add missing predicates for cmovP_regUCF

ec2959b

add TEMP(dst)

3fb569c

sviswa7 approved these changes May 12, 2025

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openjdk bot added the ready Pull request is ready to be integrated label May 12, 2025

TobiHartmann approved these changes May 14, 2025

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jatin-bhateja approved these changes May 14, 2025

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openjdk bot added the sponsor Pull request is ready to be sponsored label May 14, 2025

openjdk bot added the integrated Pull request has been integrated label May 14, 2025

openjdk bot closed this May 14, 2025

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review sponsor Pull request is ready to be sponsored labels May 14, 2025

8356281: Fix for TestFPComparison failure due to incorrect result #25101

8356281: Fix for TestFPComparison failure due to incorrect result #25101

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