[release/5.0-rc2] Disable arm64 intrinsics in UTF-16 validation code paths

[github-actions]

Backport of #42052 to release/5.0-rc2 to fix#41699, which is a performance regression in UTF8/UTF-16 code paths that was introduced during our ARM64 Optimization effort during Preview 8 and discovered during our 5.0 perf sign-off effort.

Customer Impact

Disables the ARM64-intrinsicified UTF-16 validation code paths since they ended up having poorer performance characteristics for non-ASCII data compared to their 3.x counterparts. With this PR, we skip the ARM64 intrinsics entirely but stay within vectorized code as much as possible. The codegen and perf should be on-par with what shipped in 3.x.

Here are the regressions that were found in Utf8Encoding.GetByteCount that this PR would resolve:

Method	Runtime	Input	Mean	Ratio
GetByteCount	.NET Core 3.1	EnglishAllAscii	38.00 us	1.00
GetByteCount	.NET Core 5.0	EnglishAllAscii	40.66 us	1.07
GetByteCount	.NET Core 3.1	EnglishMostlyAscii	117.50 us	1.00
GetByteCount	.NET Core 5.0	EnglishMostlyAscii	221.40 us	1.88
GetByteCount	.NET Core 3.1	Chinese	53.34 us	1.00
GetByteCount	.NET Core 5.0	Chinese	90.21 us	1.69
GetByteCount	.NET Core 3.1	Cyrillic	45.35 us	1.00
GetByteCount	.NET Core 5.0	Cyrillic	76.01 us	1.68
GetByteCount	.NET Core 3.1	Greek	58.36 us	1.00
GetByteCount	.NET Core 5.0	Greek	97.41 us	1.67

Testing

We have extensive unit test coverage of this area and all tests are passing. We still need to complete performance runs with this fix merged into master, but we will collect that data to verify that the regressions are eliminated before merging this into RC2.

Risk

Low. We are bypassing the intrinsics code path and falling back to the previous code path used, with good unit test coverage across the area.

Once this change is in, we can re-introduce tweaked versions of the ARM64 code path, validate the perf numbers, and consider a cherry-pick of the "real" fix into the 5.x servicing branches if we see performance improvements that would justify the servicing.

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[danmoseley]

@GrabYourPitchforks or @adamsitnik could one of you please fill in template?

[jeffhandley]

I'll fill in the template....

[danmoseley]

@dotnet/dnceng this is a new one:

.packages\microsoft.dotnet.helix.sdk\5.0.0-beta.20453.7\tools\Microsoft.DotNet.Helix.Sdk.MultiQueue.targets(54,5): error : (NETCORE_ENGINEERING_TELEMETRY=Helix) RestApiException: The response contained an invalid status code 429 Body: {"Message":"API rate limit exceeded. Maximum allowed 90 per 1m.","ActivityId":"e924d70d316431438a6526b0eeb243c1"}
at Microsoft.DotNet.Helix.Client.Job.OnPassFailFailed(Request req, Response res) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/Job.cs:line 322
at Microsoft.DotNet.Helix.Client.Job.PassFailAsync(String job, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/Job.cs:line 302
at Microsoft.DotNet.Helix.Sdk.WaitForHelixJobCompletion.WaitForHelixJobAsync(String jobName, String queueName, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Sdk/WaitForHelixJobCompletion.cs:line 38
at Microsoft.DotNet.Helix.Sdk.WaitForHelixJobCompletion.ExecuteCore(CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Sdk/WaitForHelixJobCompletion.cs:line 26
at Microsoft.DotNet.Helix.Sdk.HelixTask.Execute() in /_/src/Microsoft.DotNet.Helix/Sdk/HelixTask.cs:line 51

https://github.com/dotnet/runtime/pull/42064/checks?check_run_id=1096236869

[ghost]

@danmosemsft This was fallout from switching to the new service fabric API which was reverted today. New runs should not see this: https://github.com/dotnet/core-eng/issues/10759

[danmoseley]

Thanks @riarenas

[danmoseley]

Presumably this means there was a hole in our microbenchmarks (for non ASCII) -- is that tracked by dotnet/performance#1512?

[jeffhandley]

Presumably this means there was a hole in our microbenchmarks (for non ASCII) -- is that tracked by dotnet/performance#1512?

That is correct; thanks for calling that out, @danmosemsft.

[jeffhandley]

@GrabYourPitchforks / @adamsitnik - This backport was approved, but before we merge into RC2, we need to re-run the benchmarks and verify that we got the expected results. Could one of you do that and post the results here please?

[jeffhandley]

I overlooked @adamsitnik's comment on the PR for master.

@carlossanlop - are you set up to be able to build this and run the benchmarks?

[carlossanlop]

@jeffhandley I can verify this in my WSL2. I'll run the performance tests before and after the changes in this PR.

[carlossanlop]

I built the runtime repo in my WSL2 using release/5.0-rc2 as the base, and release/5.0-rc2 + this PR's change cherry-picked as the diff. Results:

root@calopearm:/home/calope/performance/src/tools/ResultsComparer# /home/calope/runtime/.dotnet/dotnet run --base /home/calope/pitchforks_before/ --diff /home/calope/pitchforks_after/ --threshold 0.01%
summary:
better: 8, geomean: 1.520
worse: 1, geomean: 1.156
total diff: 9
| Slower | diff/base | Base Median (ns) | Diff Median (ns) | Modality|
| ------------------------------------------------------------------ | ---------:| ----------------:| ----------------:| --------:|
| System.Text.Perf_Utf8Encoding.GetByteCount(Input: EnglishAllAscii) | 1.16 | 29047.75 | 33568.81 | |
| Faster | base/diff | Base Median (ns) | Diff Median (ns) | Modality|
| --------------------------------------------------------------------- | ---------:| ----------------:| ----------------:| -------- |
| System.Text.Perf_Utf8Encoding.GetByteCount(Input: Cyrillic) | 2.08 | 67897.12 | 32697.20 | several?|
| System.Text.Perf_Utf8Encoding.GetByteCount(Input: Chinese) | 1.96 | 63074.59 | 32121.14 | |
| System.Text.Perf_Utf8Encoding.GetByteCount(Input: Greek) | 1.79 | 69171.05 | 38577.66 | |
| System.Text.Perf_Utf8Encoding.GetByteCount(Input: EnglishMostlyAscii) | 1.71 | 157169.23 | 91817.25 | |
| System.Text.Perf_Utf8Encoding.GetBytes(Input: EnglishMostlyAscii) | 1.32 | 287968.96 | 218270.16 | |
| System.Text.Perf_Utf8Encoding.GetString(Input: Chinese) | 1.28 | 390277.00 | 305710.81 | |
| System.Text.Perf_Utf8Encoding.GetBytes(Input: Chinese) | 1.27 | 240803.25 | 190089.55 | |
| System.Text.Perf_Utf8Encoding.GetBytes(Input: Greek) | 1.07 | 268047.54 | 250588.14 | several?|

[GrabYourPitchforks]

Thank you for the confirmation, Carlos! :)

[jeffhandley]

Thanks, @carlossanlop! That data is super clear and matches expectations based on what we previously observed. I'll go ahead and merge.