8303278: Imprecise bottom type of ExtractB/UB #13070

e1iu · 2023-03-17T06:14:00Z

This is a trivial patch, which fixes the bottom type of ExtractB/UB nodes.

ExtractNode can be generated by Vector API Vector.lane(int), which gets the lane element at the given index. A more precise type of range can help to optimize out unnecessary type conversion in some cases.

Below shows a typical case used ExtractBNode

  public static byte byteLt16() {
   ByteVector vecb = ByteVector.broadcast(ByteVector.SPECIES_128, 1);
   return vecb.lane(1);
  }

In this case, c2 constructs IR graph like:

ExtractB  ConI(24)
   |     __|
   |    /  |
LShiftI  __|
   |    /
RShiftI

which generates AArch64 code:

movi v16.16b, #0x1
smov x11, v16.b[1]
sxtb w0, w11

with this patch, this shift pair can be optimized out by RShiftI's identity [1]. The code is optimized to:

movi v16.16b, #0x1
smov x0, v16.b[1]

[TEST]

Full jtreg passed except 4 files on x86:

jdk/incubator/vector/Byte128VectorTests.java
jdk/incubator/vector/Byte256VectorTests.java
jdk/incubator/vector/Byte512VectorTests.java
jdk/incubator/vector/Byte64VectorTests.java

They are caused by a known issue on x86 [2].

[1]

jdk/src/hotspot/share/opto/mulnode.cpp

Line 1052 in 742bc04

if (lo <= t11->_lo && t11->_hi <= hi) {

[2] https://bugs.openjdk.org/browse/JDK-8303508

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Issue

JDK-8303278: Imprecise bottom type of ExtractB/UB

Reviewers

Quan Anh Mai (@merykitty - Committer) ⚠️ Review applies to 29e99153
Tobias Hartmann (@TobiHartmann - Reviewer)

Reviewing

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$ git fetch https://git.openjdk.org/jdk.git pull/13070/head:pull/13070
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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/13070/head

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$ git pr checkout 13070

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Link to Webrev Comment

This is a trivial patch, which fixes the bottom type of ExtractB/UB nodes. ExtractNode can be generated by Vector API Vector.lane(int), which gets the lane element at the given index. A more precise type of range can help to optimize out unnecessary type conversion in some cases. Below shows a typical case used ExtractBNode ``` public static byte byteLt16() { ByteVector vecb = ByteVector.broadcast(ByteVector.SPECIES_128, 1); return vecb.lane(1); } ``` In this case, c2 constructs IR graph like: ExtractB ConI(24) | __| | / | LShiftI __| | / RShiftI which generates AArch64 code: movi v16.16b, #0x1 smov x11, v16.b[1] sxtb w0, w11 with this patch, this shift pair can be optimized out by RShiftI's identity [1]. The code is optimized to: movi v16.16b, #0x1 smov x0, v16.b[1] [TEST] Full jtreg passed except 4 files on x86: jdk/incubator/vector/Byte128VectorTests.java jdk/incubator/vector/Byte256VectorTests.java jdk/incubator/vector/Byte512VectorTests.java jdk/incubator/vector/Byte64VectorTests.java They are caused by a known issue on x86 [2]. [1] https://github.com/openjdk/jdk/blob/742bc041eaba1ff9beb7f5b6d896e4f382b030ea/src/hotspot/share/opto/mulnode.cpp#L1052 [2] https://bugs.openjdk.org/browse/JDK-8303508 Change-Id: Ibea9aeacb41b4d1c5b2621c7a97494429394b599

bridgekeeper · 2023-03-17T06:15:15Z

👋 Welcome back eliu! 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 · 2023-03-17T06:17:05Z

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

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mlbridge · 2023-03-17T06:21:16Z

Webrevs

01: Full - Incremental (12748c7a)
00: Full (29e99153)

TobiHartmann

~~Looks good to me too.~~

TobiHartmann

This triggers failures in testing:

jdk/incubator/vector/Byte64VectorTests.java

java.lang.Exception: failures: 1
	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:95)
	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:53)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:125)
	at java.base/java.lang.Thread.run(Thread.java:1623)

e1iu · 2023-03-21T01:52:02Z

This triggers failures in testing:

jdk/incubator/vector/Byte64VectorTests.java

java.lang.Exception: failures: 1
	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:95)
	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:53)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:125)
	at java.base/java.lang.Thread.run(Thread.java:1623)

I think this should be caused by https://bugs.openjdk.org/browse/JDK-8303508. The removed narrowing exposed this issue on x86, that the generated code of ExtractB perhaps does not handle sign-bit correctly. TBH I'm not familiar with x86 instructions... @jatin-bhateja Could you help to take a look at this bug?

merykitty · 2023-03-21T02:35:25Z

Yes x86 does not handle signed extension correctly. pextrb and pextrw zeroes the upper bits instead of signed extending them. A simple fix is to add movsx after those.

jdk/src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp

Line 2247 in bbca7c3

    
           void C2_MacroAssembler::extract(BasicType bt, Register dst, XMMRegister src, int idx) {

jatin-bhateja · 2023-03-22T15:27:52Z

Yes x86 does not handle signed extension correctly. pextrb and pextrw zeroes the upper bits instead of signed extending them. A simple fix is to add movsx after those.

jdk/src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp

Line 2247 in bbca7c3

void C2_MacroAssembler::extract(BasicType bt, Register dst, XMMRegister src, int idx) {

As can be seen above C2 creates ExtractS node with TypeInt::SHORT which is then succeeded by ConvI2L node since expander returns a long value.
Return value is again down casted back short value though an explicit cast operation in java code.

Currently C2 folds following IR sequence

ExtractS  -> ConvI2L -> ConvL2I ->  LShift (16) -> RShift(16)                   ==>  ExtractS -> return_value
    [Inline expander]    [ Java side down cast long to short -> l2i + i2s]

Because ideal type of ExtractS is TypeInt::SHORT hence entire chain of conversion operations are folded by compiler during idealizations.

There are two ways to address this issue:-

We can set the ideal type of ExtractS node to TypeInt::INT as is done for ExtractB/UB since subsequent java code will handle down casting to generate correct result. This will also fix JDK-8303508.
Enforce strict semantics of ExtractS/B IR node and thus backends should emit an explicit sign extension instruction movsx for sub-word types.

I agree with @merykitty that 2) solution looks more robust since it will enforce accurate semantics of ExtractS IR.

Change-Id: I40cce803da09bae31cd74b86bf93607a08219545

e1iu · 2023-03-30T08:11:53Z

@TobiHartmann Could you help to take a look?

TobiHartmann

Sure, I'll re-run testing.

TobiHartmann

Looks good. All tests passed.

openjdk · 2023-04-03T05:28:38Z

@theRealELiu 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:

8303278: Imprecise bottom type of ExtractB/UB

Reviewed-by: qamai, 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 112 new commits pushed to the master branch:

b062b1b: 8304743: Compile_lock and SystemDictionary updates
df819cf: 8304945: StringBuilder and StringBuffer should implement Appendable explicitly
312bbe7: 8305485: Problemlist runtime/Thread/TestAlwaysPreTouchStacks.java
50e31e0: 8305442: (bf) Direct and view implementations of CharBuffer.toString(int, int) do not need to catch SIOBE
85e3974: 8304014: Convert test/jdk/java/util/zip/ZipFile/CorruptedZipFiles.java to junit
40aea04: 8278268: (ch) InputStream returned by Channels.newInputStream should have fast path for FileChannel targets
9b9b5a7: 8302323: Add repeat methods to StringBuilder/StringBuffer
dd7ca75: 8305478: [REDO] disable gtest/NMTGtests.java sub-tests failing due to JDK-8305414
f9827ad: 8288109: HttpExchangeImpl.setAttribute does not allow null value after JDK-8266897
6010de0: 8305417: disable gtest/NMTGtests.java sub-tests failing due to JDK-8305414
... and 102 more: https://git.openjdk.org/jdk/compare/38e17148faef7799515478bd834ed2fa1a5153de...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.

e1iu · 2023-04-04T01:17:03Z

/integrate

openjdk · 2023-04-04T01:18:21Z

Going to push as commit ac898e9.
Since your change was applied there have been 116 commits pushed to the master branch:

a1a9ec6: 8297286: runtime/vthread tests crashing after JDK-8296324
c6bd489: 8305206: Add @SPEC tags in java.base/java.* (part 1)
ccbb0e8: 8303798: REDO - Remove fdlibm C sources
9ce5fdc: 8305421: Work around JDK-8305420 in CDSJDITest.java
b062b1b: 8304743: Compile_lock and SystemDictionary updates
df819cf: 8304945: StringBuilder and StringBuffer should implement Appendable explicitly
312bbe7: 8305485: Problemlist runtime/Thread/TestAlwaysPreTouchStacks.java
50e31e0: 8305442: (bf) Direct and view implementations of CharBuffer.toString(int, int) do not need to catch SIOBE
85e3974: 8304014: Convert test/jdk/java/util/zip/ZipFile/CorruptedZipFiles.java to junit
40aea04: 8278268: (ch) InputStream returned by Channels.newInputStream should have fast path for FileChannel targets
... and 106 more: https://git.openjdk.org/jdk/compare/38e17148faef7799515478bd834ed2fa1a5153de...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-04-04T01:18:31Z

@theRealELiu Pushed as commit ac898e9.

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

openjdk bot added the rfr Pull request is ready for review label Mar 17, 2023

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Mar 17, 2023

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jatin-bhateja mentioned this pull request Mar 23, 2023

8303508: Vector.lane() gets wrong value on x86 #13152

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12748c7

Change-Id: I40cce803da09bae31cd74b86bf93607a08219545

e1iu requested a review from TobiHartmann March 29, 2023 02:41

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e1iu deleted the ENTLLT-5267-external branch July 10, 2023 09:53

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8303278: Imprecise bottom type of ExtractB/UB #13070

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8303278: Imprecise bottom type of ExtractB/UB #13070

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