Vector128.ShuffleUnsafe #88559

AlexRadch · 2023-07-09T23:13:01Z

Close #81609 issue.

dotnet-issue-labeler · 2023-07-09T23:13:07Z

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ghost · 2023-07-09T23:13:12Z

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Issue Details

Close #81609 issue.

Author:	AlexRadch
Assignees:	-
Labels:	`area-System.Runtime.Intrinsics`, `new-api-needs-documentation`
Milestone:	-

EgorBo · 2023-07-10T14:51:46Z

Test failures look related

…/> support, indices are treated as modulo 32.

tannergooding · 2023-07-10T19:46:05Z

src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Vector256.cs

+            if (AdvSimd.Arm64.IsSupported)
+            {
+                (Vector128<byte>, Vector128<byte>) table = (vector.GetLower(), vector.GetUpper());
+                return Vector256.Create(
+                    AdvSimd.Arm64.VectorTableLookup(table, indices.GetLower()),
+                    AdvSimd.Arm64.VectorTableLookup(table, indices.GetUpper()));
+            }
+
+            if (PackedSimd.IsSupported)
+            {
+                return Vector256.Create(
+                    PackedSimd.Shuffle(vector.GetLower(), vector.GetUpper(), indices.GetLower()),
+                    PackedSimd.Shuffle(vector.GetLower(), vector.GetUpper(), indices.GetUpper()));
+            }


We shouldn't need this additional handling for V256/V512. It isn't expected that users are calling these, let alone expecting good performance, when IsHardwareAccelerated reports false.

It's just causing the JIT to spend more time doing dead code elimination, managing the inliner budget, etc.

MihaZupan · 2023-07-10T19:49:06Z

src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Vector256.cs

+        {
+            if (Avx2.IsSupported)
+            {
+                return Avx2.Shuffle(vector, indices);


These hardware intrinsics have different semantics than Vector256/512 Shuffles.

Avx2.Shuffle is effectively two Vector128.Shuffles on each half. The indices are still [0, 15]. Similar for Avx512.

Vector256.Shuffle on the other hand works with the whole vector and allows you to pick and index [0, 31].

tannergooding · 2023-07-10T19:51:38Z

src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Vector256.cs

+        /// <remarks>Unlike Shuffle, this method delegates to the underlying hardware intrinsic without ensuring that <paramref name="indices"/> are normalized to [0, 31].
+        /// On hardware with <see cref="Avx2"/> support, indices are treated as modulo 32, and if the high bit is set, the result will be set to 0 for that element.
+        /// On hardware with <see cref="AdvSimd.Arm64"/> support, this method behaves the same as Shuffle.</remarks>
+        /// On hardware with <see cref="PackedSimd"/> support, indices are treated as modulo 32.


nit: This remarks is confusing. Shuffle doesn't ensure the indices are normalized. It simply treats all out of range indices as setting the result to 0.

Unsafe simply changes how out of range indices are handled and allows it to differ based on the target hardware. In the case of xarch most out of range indices are handled as mod 32. But indices with the MSB set are set to 0 instead.

We can probably exclude the Arm64/Wasm callouts for V256/V512 as they aren't important. They can be combined into a general statement that other platforms will treat this the same as Shuffle

stephentoub · 2023-07-17T14:54:58Z

src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Vector128.cs

@@ -2384,7 +2384,7 @@ public static Vector128<sbyte> Shuffle(Vector128<sbyte> vector, Vector128<sbyte>
        [CompExactlyDependsOn(typeof(AdvSimd))]
        [CompExactlyDependsOn(typeof(AdvSimd.Arm64))]
        [CompExactlyDependsOn(typeof(PackedSimd))]
-        internal static Vector128<byte> ShuffleUnsafe(Vector128<byte> vector, Vector128<byte> indices)
+        public static Vector128<byte> ShuffleUnsafe(Vector128<byte> vector, Vector128<byte> indices)


Is there anywhere else this should be consumed in dotnet/runtime as part of making it public?

I believe I updated all such places when adding the internal helper as part of #80963

Ok. I know you updated places in corelib. I was wondering if there were places outside of corelib you couldn't update. Sounds like no.

There are two places I saw where we still use the platform-specific instructions directly (BitArray and OptimizedInboxTextEncoder), but both of those are in larger platform-specific blocks of logic, so there was no reason to replace them.

adamsitnik

Plenty of related tests are failing. Example:

Test System.Runtime.Intrinsics.Tests.Vectors.Vector256Tests.Vector256ByteShuffleOneInputWithLocalIndicesTest has failed

Please address the comments posted by other reviewers and fix the tests.

Thank you for your contribution!

ghost · 2023-11-03T21:01:24Z

This pull request has been automatically marked no-recent-activity because it has not had any activity for 14 days. It will be closed if no further activity occurs within 14 more days. Any new comment (by anyone, not necessarily the author) will remove no-recent-activity.

ghost · 2023-11-18T00:01:30Z

This pull request will now be closed since it had been marked no-recent-activity but received no further activity in the past 14 days. It is still possible to reopen or comment on the pull request, but please note that it will be locked if it remains inactive for another 30 days.

Vector128.ShuffleUnsafe

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dotnet-issue-labeler bot added area-System.Runtime.Intrinsics new-api-needs-documentation labels Jul 9, 2023

ghost added the community-contribution Indicates that the PR has been added by a community member label Jul 9, 2023

This was referenced Jul 10, 2023

[mono][tvos] Failing Vector64/128 tests #87164

Closed

LibraryImportGenerator.Unit.Tests crashed in CI #87951

Closed

simpleruntimeeventvalidation test failing in CI #88499

Closed

runfoapp bot mentioned this pull request Jul 10, 2023

Infra improvements for Helix #68176

Closed

AlexRadch added 3 commits July 11, 2023 02:28

Vector256<byte>.ShuffleUnsafe On hardware with <see cref="PackedSimd"…

76a16c9

…/> support, indices are treated as modulo 32.

lint

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tannergooding reviewed Jul 10, 2023

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MihaZupan reviewed Jul 10, 2023

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tannergooding reviewed Jul 10, 2023

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build-analysis bot mentioned this pull request Jul 11, 2023

Test failure readytorun/HardwareIntrinsics/X86/CpuId_R2R_Avx/CpuId_R2R_Avx.sh #88582

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stephentoub reviewed Jul 17, 2023

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adamsitnik requested changes Oct 19, 2023

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ghost added the needs-author-action An issue or pull request that requires more info or actions from the author. label Oct 19, 2023

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AlexRadch deleted the Vector128.ShuffleUnsafe branch January 12, 2025 11:53

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Vector128.ShuffleUnsafe #88559

Vector128.ShuffleUnsafe #88559

AlexRadch commented Jul 9, 2023

dotnet-issue-labeler bot commented Jul 9, 2023

ghost commented Jul 9, 2023

EgorBo commented Jul 10, 2023

tannergooding Jul 10, 2023

MihaZupan Jul 10, 2023

tannergooding Jul 10, 2023

stephentoub Jul 17, 2023

MihaZupan Jul 17, 2023

stephentoub Jul 17, 2023

MihaZupan Jul 17, 2023

adamsitnik left a comment

ghost commented Nov 3, 2023

ghost commented Nov 18, 2023

Vector128.ShuffleUnsafe #88559

Vector128.ShuffleUnsafe #88559

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AlexRadch commented Jul 9, 2023

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