runtime: .NET 7 exception on Android with EnableLLVM=true

Description

Run with LLVM on an arm64 device, and you can run into:

07-22 09:59:55.062  4374  4374 F mono-rt : [ERROR] FATAL UNHANDLED EXCEPTION: System.PlatformNotSupportedException: Arg_PlatformNotSupported
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.Text.ASCIIUtility.GetIndexOfFirstNonAsciiByte_Intrinsified(Byte* , UIntPtr )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.Text.Unicode.Utf8Utility.GetPointerToFirstInvalidByte(Byte* , Int32 , Int32& , Int32& )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.Text.UTF8Encoding.GetCharCount(Byte* , Int32 )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.String.CreateStringFromEncoding(Byte* , Int32 , Encoding )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.Text.Encoding.GetString(Byte* , Int32 )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.String.CreateStringForSByteConstructor(Byte* , Int32 )
07-22 09:59:55.062  4374  4374 F mono-rt :    at System.String.Ctor(SByte* value)
07-22 09:59:55.062  4374  4374 F mono-rt :    at Java.Interop.TypeManager.GetClassName(IntPtr )
07-22 09:59:55.062  4374  4374 F mono-rt :    at Android.Runtime.JNIEnv.RegisterJniNatives(IntPtr , Int32 , IntPtr , IntPtr , Int32 )

Somewhere here:

https://github.com/dotnet/runtime/blob/b31a48ae77cf20729387383d15e207f838b0a076/src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs#L88

So I think AdvSimd.Arm64.IsSupported is true, but because GetIndexOfFirstNonAsciiByte_Intrinsified() is not in the AOT profile (it’s running under JIT), we get the above exception. It’s possible that the above code should also work under JIT.

/cc @fanyang-mono

Reproduction Steps

1. dotnet new android
2. dotnet build -t:Run -c Release -p:EnableLLVM=true to run on an arm64 device (in my case a Pixel 5)

Expected behavior

You can use Profiled AOT + LLVM together on Android.

Actual behavior

We get an exception when trying to use Profiled AOT + LLVM together on Android.

Regression?

I don’t hit this same exception in .NET 6, but maybe it’s just luck?

Known Workarounds

You can turn off profiled AOT, such as -p:AndroidEnableProfiledAot=false or don’t use LLVM.

Configuration

.NET 7.0.100-rc.1.22374.1

Other information

No response