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8297172: Fix some issues of auto-vectorization of Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros() #11405

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@fg1417 fg1417 commented Nov 29, 2022

Background:

Java API[1] for Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros() returns int type, while Vector API[2] for them returns long type. Currently, to support auto-vectorization of Java API and Vector API at the same time, some vector platforms, namely aarch64 and x86, provides two types of vector nodes taking long type: One produces long vector type for vector API, and the other one produces int vector type by casting long-type result from the first one.

We can move the casting work for auto-vectorization of Java API to the mid-end so that we can unify the vector implementation in the backend, reducing extra code. The patch does the refactoring and also fixes several issues below.

  1. Refine the auto-vectorization of Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros()

In the patch, during the stage of generating vector node for the candidate pack, to implement the complete behavior of these Java APIs, superword will make two consecutive vector nodes: the first one, the same as Vector API, does the real execution to produce long-type result, and the second one casts the result to int vector type.

For those platforms, which have supported correctly vectorizing these java APIs before, the patch has no real impact on final generated assembly code and, consequently, has no performance regression.

  1. Fix the IR check failure of compiler/vectorization/TestPopCountVectorLong.java on 128-bit sve platform

These Java APIs take a long type and produce an int type, like conversion nodes between different data sizes do. In superword, the alignment of their input nodes is different from their own. It results in that these APIs can't be vectorized when
-XX:MaxVectorSize=16. So, the IR check for vector nodes in compiler/vectorization/TestPopCountVectorLong.java would fail. To fix the issue of alignment, the patch corrects their related alignment, just like it did for conversion nodes between different data sizes. After the patch, these Java APIs can be vectorized on 128-bit platforms, as long as the auto-vectorization is profitable.

  1. Fix the incorrect vectorization of numberOfTrailingZeros/numberOfLeadingZeros() in aarch64 platforms with more than 128 bits

Although Long.NumberOfLeadingZeros/NumberOfTrailingZeros() can be vectorized on sve platforms when
-XX:MaxVectorSize=32 or -XX:MaxVectorSize=64 even before the patch, aarch64 backend didn't provide special vector implementation for Java API and thus the generated code is not correct, like:

LOOP:
  sxtw  x13, w12
  add   x14, x15, x13, uxtx #3
  add   x17, x14, #0x10
  ld1d  {z16.d}, p7/z, [x17]
  // Incorrectly use integer rbit/clz insn for long type vector
 *rbit  z16.s, p7/m, z16.s
 *clz   z16.s, p7/m, z16.s
  add   x13, x16, x13, uxtx #2
  str   q16, [x13, #16]
  ...
  add   w12, w12, #0x20
  cmp   w12, w3
  b.lt  LOOP

It causes a runtime failure of the testcase compiler/vectorization/TestNumberOfContinuousZeros.java added in the patch. After the refactoring, the testcase can pass and the code is corrected:

LOOP:
  sxtw  x13, w12
  add   x14, x15, x13, uxtx #3
  add   x17, x14, #0x10
  ld1d  {z16.d}, p7/z, [x17]
  // Compute with long vector type and convert to int vector type
 *rbit  z16.d, p7/m, z16.d
 *clz   z16.d, p7/m, z16.d
 *mov   z24.d, #0
 *uzp1  z25.s, z16.s, z24.s
  add   x13, x16, x13, uxtx #2
  str   q25, [x13, #16]
  ...
  add   w12, w12, #0x20
  cmp   w12, w3
  b.lt  LOOP
  1. Fix an assertion failure on x86 avx2 platform

Before, on x86 avx2 platform, there is an assertion failure when C2 tries to vectorize the loops like:

//  long[] ia;
//  int[] ic;
    for (int i = 0; i < LENGTH; ++i) {
      ic[i] = Long.numberOfLeadingZeros(ia[i]);
    }

X86 backend supports vectorizing numberOfLeadingZeros() on avx2 platform, but it uses evpmovqd() to do casting for CountLeadingZerosV[3], which can only be used when UseAVX > 2[4]. After the refactoring, the failure can be fixed naturally.

Tier 1~3 passed with no new failures on Linux AArch64/X86 platform.

[1] https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#bitCount(long)
https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#numberOfTrailingZeros(long)
https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#numberOfLeadingZeros(long)
[2]

v0.uOp(m, (i, a) -> (long) Long.bitCount(a));

[3]
__ evpmovqd($dst$$XMMRegister, $dst$$XMMRegister, vlen_enc);

[4]
assert(UseAVX > 2, "");


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  • Commit message must refer to an issue

Issue

  • JDK-8297172: Fix some issues of auto-vectorization of Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros()

Reviewers

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/11405/head:pull/11405
$ git checkout pull/11405

Update a local copy of the PR:
$ git checkout pull/11405
$ git pull https://git.openjdk.org/jdk pull/11405/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 11405

View PR using the GUI difftool:
$ git pr show -t 11405

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/11405.diff

…erOfTrailingZeros/numberOfLeadingZeros()`

Background:

Java API[1] for `Long.bitCount/numberOfTrailingZeros/
numberOfLeadingZeros()` returns int type, while Vector API[2]
for them returns long type. Currently, to support
auto-vectorization of Java API and Vector API at the same time,
some vector platforms, namely aarch64 and x86, provides two types
of vector nodes taking long type: One produces long vector type
for vector API, and the other one produces int vector type by
casting long-type result from the first one.

We can move the casting work for auto-vectorization of Java API
to the mid-end so that we can unify the vector implementation in
the backend, reducing extra code. The patch does the refactoring
and also fixes several issues below.

1. Refine the auto-vectorization of
`Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros()`

In the patch, during the stage of generating vector node for the
candidate pack, to implement the complete behavior of these
Java APIs, superword will make two consecutive vector nodes:
the first one, the same as Vector API, does the real execution
to produce long-type result, and the second one casts the result
to int vector type.

For those platforms, which have supported correctly vectorizing
these java APIs before, the patch has no real impact on final
generated assembly code and, consequently, has no performance
regression.

2. Fix the IR check failure of
`compiler/vectorization/TestPopCountVectorLong.java` on
128-bit sve platform

These Java APIs take a long type and produce an int type, like
conversion nodes between different data sizes do. In superword,
the alignment of their input nodes is different from their own.
It results in that these APIs can't be vectorized when
`-XX:MaxVectorSize=16`. So, the IR check for vector nodes in
`compiler/vectorization/TestPopCountVectorLong.java` would fail.
To fix the issue of alignment, the patch corrects their related
alignment, just like it did for conversion nodes between
different data sizes. After the patch, these Java APIs can be
vectorized on 128-bit platforms, as long as the auto-
vectorization is profitable.

3. Fix the incorrect vectorization of
`numberOfTrailingZeros/numberOfLeadingZeros()` in aarch64
platforms with more than 128 bits

Although `Long.NumberOfLeadingZeros/NumberOfTrailingZeros()` can
be vectorized on sve platforms when `-XX:MaxVectorSize=32` or
`-XX:MaxVectorSize=64` even before the patch, aarch64 backend
didn't provide special vector implementation for Java API and
thus the generated code is not correct, like:
```
LOOP:
  sxtw  x13, w12
  add   x14, x15, x13, uxtx openjdk#3
  add   x17, x14, #0x10
  ld1d  {z16.d}, p7/z, [x17]
  // Incorrectly use integer rbit/clz insn for long type vector
 *rbit  z16.s, p7/m, z16.s
 *clz   z16.s, p7/m, z16.s
  add   x13, x16, x13, uxtx openjdk#2
  str   q16, [x13, openjdk#16]
  ...
  add   w12, w12, #0x20
  cmp   w12, w3
  b.lt  LOOP
```

It causes a runtime failure of the testcase
`compiler/vectorization/TestNumberOfContinuousZeros.java` added
in the patch. After the refactoring, the testcase can pass and
the code is corrected:
```
LOOP:
  sxtw  x13, w12
  add   x14, x15, x13, uxtx openjdk#3
  add   x17, x14, #0x10
  ld1d  {z16.d}, p7/z, [x17]
  // Compute with long vector type and convert to int vector type
 *rbit  z16.d, p7/m, z16.d
 *clz   z16.d, p7/m, z16.d
 *mov   z24.d, #0
 *uzp1  z25.s, z16.s, z24.s
  add   x13, x16, x13, uxtx openjdk#2
  str   q25, [x13, openjdk#16]
  ...
  add   w12, w12, #0x20
  cmp   w12, w3
  b.lt  LOOP
```

4. Fix an assertion failure on x86 avx2 platform

Before, on x86 avx2 platform, there is an assertion failure when
C2 tries to vectorize the loops like:
```
//  long[] ia;
//  int[] ic;
    for (int i = 0; i < LENGTH; ++i) {
      ic[i] = Long.numberOfLeadingZeros(ia[i]);
    }
```

X86 backend supports vectorizing `numberOfLeadingZeros()` on
avx2 platform, but it uses `evpmovqd()` to do casting for
`CountLeadingZerosV`[3], which can only be used when
`UseAVX > 2`[4]. After the refactoring, the failure can be fixed
naturally.

Tier 1~3 passed with no new failures on Linux AArch64/X86 platform.

[1] https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#bitCount(long)
    https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#numberOfTrailingZeros(long)
    https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Long.html#numberOfLeadingZeros(long)
[2] https://github.com/openjdk/jdk/blob/544e31722528d12fae0eb19271f85886680801a6/src/jdk.incubator.vector/share/classes/jdk/incubator/vector/LongVector.java#L687
[3] https://github.com/openjdk/jdk/blob/544e31722528d12fae0eb19271f85886680801a6/src/hotspot/cpu/x86/x86.ad#L9418
[4] https://github.com/openjdk/jdk/blob/fc616588c1bf731150a9d9b80033bb589bcb231f/src/hotspot/cpu/x86/assembler_x86.cpp#L2239
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👋 Welcome back fgao! 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 openjdk bot added the rfr Pull request is ready for review label Nov 29, 2022
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@fg1417 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.

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mlbridge bot commented Nov 29, 2022

Webrevs

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Very nicely done.

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vnkozlov commented Dec 5, 2022

I suggest to wait approval from @TobiHartmann after his testing is finished.

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@fg1417 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:

8297172: Fix some issues of auto-vectorization of `Long.bitCount/numberOfTrailingZeros/numberOfLeadingZeros()`

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 169 new commits pushed to the master branch:

  • a613998: 8297689: Fix incorrect result of Short.reverseBytes() call in loops
  • f8f4630: 8297963: Partially fix string expansion issues in UTIL_DEFUN_NAMED and related macros
  • 2a243a3: 8267617: Certificate's IP x509 NameConstraints raises ArrayIndexOutOfBoundsException
  • 923c746: 8298057: (fs) Remove PollingWatchService.POLLING_INIT_DELAY
  • 0bd04a6: 8297951: C2: Create skeleton predicates for all If nodes in loop predication
  • f5ad515: 8297247: Add GarbageCollectorMXBean for Remark and Cleanup pause time in G1
  • e975418: 8298102: Remove DirtyCardToOopClosure::_last_explicit_min_done
  • 04012c4: 8298111: Cleanups after UseMallocOnly removal
  • ee9ba74: 8295184: Printing messages with a RecordComponentElement does not include position
  • ba2d28e: 8298027: Remove SCCS id's from awt jtreg tests
  • ... and 159 more: https://git.openjdk.org/jdk/compare/2f83b5c487f112c175d081ca5882f5032518937a...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 (@vnkozlov, @TobiHartmann) 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).

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Looks good to me too. All tests passed.

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fg1417 commented Dec 6, 2022

Thanks for your review and test work, @vnkozlov @TobiHartmann. I'll integrate it.

/integrate

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Your change (at version cf2a0e7) is now ready to be sponsored by a Committer.

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pfustc commented Dec 6, 2022

/sponsor

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openjdk bot commented Dec 6, 2022

Going to push as commit 4458de9.
Since your change was applied there have been 169 commits pushed to the master branch:

  • a613998: 8297689: Fix incorrect result of Short.reverseBytes() call in loops
  • f8f4630: 8297963: Partially fix string expansion issues in UTIL_DEFUN_NAMED and related macros
  • 2a243a3: 8267617: Certificate's IP x509 NameConstraints raises ArrayIndexOutOfBoundsException
  • 923c746: 8298057: (fs) Remove PollingWatchService.POLLING_INIT_DELAY
  • 0bd04a6: 8297951: C2: Create skeleton predicates for all If nodes in loop predication
  • f5ad515: 8297247: Add GarbageCollectorMXBean for Remark and Cleanup pause time in G1
  • e975418: 8298102: Remove DirtyCardToOopClosure::_last_explicit_min_done
  • 04012c4: 8298111: Cleanups after UseMallocOnly removal
  • ee9ba74: 8295184: Printing messages with a RecordComponentElement does not include position
  • ba2d28e: 8298027: Remove SCCS id's from awt jtreg tests
  • ... and 159 more: https://git.openjdk.org/jdk/compare/2f83b5c487f112c175d081ca5882f5032518937a...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Dec 6, 2022
@openjdk openjdk bot closed this Dec 6, 2022
@openjdk 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 Dec 6, 2022
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@pfustc @fg1417 Pushed as commit 4458de9.

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