8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation #122

DamonFool · 2021-01-14T12:32:41Z

Hi all,

The code-gen for VectorReinterpret may be wrong on x86.

Let's see the opto-assembly for the reproducer in the JBS, which was actually based on @XiaohongGong 's example in JDK-8259353 and many thanks to her.

066     B7: #   out( N1 ) <- in( B6 )  Freq: 0.999994
066     vector_reinterpret_expand XMM0,XMM0     !
066     store_vector [R12 + R11 << 3 + #16] (compressed oop addressing),XMM0

Please note that the dst and src [1] share the same XMM0 register and movdqu [2] should be generated for this case.
But when dst == src, movdqu actually generates nothing [3], which leads to incorrect result;

For this case, movdqu should not be empty since the upper bits of dst should be zeroed.
The similar error also exists for vmovdqu [4].

I think we should also change movflt [5] to movss but I just can't understand why we have 4-byte vectors.
Isn't the shortest vectors 8-byte on x86?

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L3354
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L3364
[3] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/macroAssembler_x86.cpp#L2490
[4] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/macroAssembler_x86.cpp#L2515
[5] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L3379

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Issue

JDK-8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation

Reviewers

Rickard Bäckman (@rickard - Reviewer)
Nils Eliasson (@neliasso - Reviewer)
Vladimir Kozlov (@vnkozlov - Reviewer)

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$ git fetch https://git.openjdk.java.net/jdk16 pull/122/head:pull/122
$ git checkout pull/122

DamonFool · 2021-01-14T12:33:09Z

/issue add JDK-8259775
/test
/label add hotspot-compiler
/cc hotspot-compiler

bridgekeeper · 2021-01-14T12:33:34Z

👋 Welcome back jiefu! 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 · 2021-01-14T12:34:12Z

@DamonFool This issue is referenced in the PR title - it will now be updated.

openjdk · 2021-01-14T12:34:19Z

@DamonFool
The hotspot-compiler label was successfully added.

openjdk · 2021-01-14T12:34:49Z

@DamonFool The hotspot-compiler label was already applied.

mlbridge · 2021-01-14T12:37:10Z

Webrevs

DamonFool · 2021-01-16T11:37:18Z

/test

DamonFool · 2021-01-20T11:23:37Z

Hi all,

The reason for the wrong execution is that the upper bits of vector registers fails to be zeroed.
This is because movdqu(XMMRegister dst, XMMRegister src) and vmovdqu(XMMRegister dst, XMMRegister src) were incorrectly optimized when dst == src after JDK-8223347 (Integration of Vector API, Oct 14 20:02:46 2020).
So this seems to be a regression of JDK-8223347.

The 4-byte vectors also be fixed by using movfltz since we are not recommended to use movss directly [1].
And the jtreg test has been added to reproduce this bug on both AVX256 and AVX512 machines.

Could you please review it?

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/macroAssembler_x86.hpp#L1048

openjdk · 2021-01-20T13:32:03Z

@DamonFool 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:

8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation

Reviewed-by: rbackman, neliasso, 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 12 new commits pushed to the master branch:

ede1bea: 8227695: assert(pss->trim_ticks().seconds() == 0.0) failed: Unexpected partial trimming during evacuation
62eab50: 8255199: Catching a few NumberFormatExceptions in xmldsig
a5367cb: 8247619: Improve Direct Buffering of Characters
0408b23: 8259757: add a regression test for 8259353 and 8259601
0120510: 8259732: JDK 16 L10n resource file update - msg drop 10
f7b96d3: 8259796: timed CompletableFuture.get may swallow InterruptedException
bb0821e: 8258643: [TESTBUG] javax/swing/JComponent/7154030/bug7154030.java failed with "Exception: Failed to hide opaque button"
cd25bf2: 8259574: SIGSEGV in BFSClosure::closure_impl
d5ca3b3: 8259641: C2: assert(early->dominates(LCA)) failed: early is high enough
e85892b: 8258396: SIGILL in jdk.jfr.internal.PlatformRecorder.rotateDisk()
... and 2 more: https://git.openjdk.java.net/jdk16/compare/5926d75fa1a96e001c4167a4352e55024644adad...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.

neliasso

Good to know that the code was introduced in 16 so that no regression is introduced.

Approved.

vnkozlov

Don't forget to request approval for JDK 16 fix integration:
http://openjdk.java.net/jeps/3#Fix-Request-Process

vnkozlov · 2021-01-20T17:42:30Z

src/hotspot/cpu/x86/macroAssembler_x86.hpp

@@ -168,6 +168,9 @@ class MacroAssembler: public Assembler {
  void movflt(XMMRegister dst, AddressLiteral src);
  void movflt(Address dst, XMMRegister src) { movss(dst, src); }

+  // Move with zero extension
+  void movfltz(XMMRegister dst, XMMRegister src) { movss(dst, src); }


Seems movdbl(XMMRegister dst, XMMRegister src) has the same issue.

Seems movdbl(XMMRegister dst, XMMRegister src) has the same issue.

Good catch.
I will try to make a reproducer and fix it in another pr since VectorReinterpret doesn't use it.
Thanks.

DamonFool · 2021-01-21T00:00:26Z

Thanks @rickard , @neliasso and @vnkozlov for your review and comments.

@vnkozlov , jdk16-fix-request has been added in the JBS.
Thanks.

DamonFool · 2021-01-21T23:26:32Z

Will integrate it later since the jdk16-fix-request will be approved after PR is finished.
Thanks.

vnkozlov

I approved this fix for JDK 16.
I misread your comment and thought you will also fix movdbl() here.
I am fine with fixing it in separate PR.

DamonFool · 2021-01-22T00:11:56Z

/integrate

openjdk · 2021-01-22T00:14:32Z

@DamonFool Since your change was applied there have been 12 commits pushed to the master branch:

ede1bea: 8227695: assert(pss->trim_ticks().seconds() == 0.0) failed: Unexpected partial trimming during evacuation
62eab50: 8255199: Catching a few NumberFormatExceptions in xmldsig
a5367cb: 8247619: Improve Direct Buffering of Characters
0408b23: 8259757: add a regression test for 8259353 and 8259601
0120510: 8259732: JDK 16 L10n resource file update - msg drop 10
f7b96d3: 8259796: timed CompletableFuture.get may swallow InterruptedException
bb0821e: 8258643: [TESTBUG] javax/swing/JComponent/7154030/bug7154030.java failed with "Exception: Failed to hide opaque button"
cd25bf2: 8259574: SIGSEGV in BFSClosure::closure_impl
d5ca3b3: 8259641: C2: assert(early->dominates(LCA)) failed: early is high enough
e85892b: 8258396: SIGILL in jdk.jfr.internal.PlatformRecorder.rotateDisk()
... and 2 more: https://git.openjdk.java.net/jdk16/compare/5926d75fa1a96e001c4167a4352e55024644adad...master

Your commit was automatically rebased without conflicts.

Pushed as commit d90e06a.

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

8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation

f00904b

openjdk bot added the rfr label Jan 14, 2021

openjdk bot added the hotspot-compiler label Jan 14, 2021

DamonFool added 3 commits Jan 16, 2021

Add a jtreg test

db5d758

Add tests for both 256 and 512 vectors

e17ba6c

Zero upper bits of 4-byte vectors

d86bf85

Refine the test to always reproduce the bug

94350c0

rickard approved these changes Jan 20, 2021

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openjdk bot added the ready label Jan 20, 2021

rickard approved these changes Jan 20, 2021

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neliasso approved these changes Jan 20, 2021

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vnkozlov reviewed Jan 20, 2021

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vnkozlov approved these changes Jan 21, 2021

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openjdk bot closed this Jan 22, 2021

openjdk bot added the integrated label Jan 22, 2021

openjdk bot removed ready rfr labels Jan 22, 2021

DamonFool deleted the JDK-8259775 branch Jan 22, 2021

8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation #122

8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation #122

DamonFool commented Jan 14, 2021 •

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8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation #122

8259775: [Vector API] Incorrect code-gen for VectorReinterpret operation #122

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DamonFool commented Jan 14, 2021 • edited by openjdk[bot] bot

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