Mono's Vector128 support incorrectly handles Abs for signed integer MinValue

[stephentoub]

Repro:
#95588

        [Fact]
        public void Vector128SByteAbs_MinValue()
        {
            Vector128<sbyte> vector = Vector128.Create(sbyte.MinValue);
            Vector128<sbyte> abs = Vector128.Abs(vector);
            for (int index = 0; index < Vector128<sbyte>.Count; index++)
            {
                Assert.Equal(sbyte.MinValue, vector.GetElement(index));
            }
        }

This test passes on coreclr. On mono it fails with:

    System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue [FAIL]
      System.OverflowException : Negating the minimum value of a twos complement number is invalid.
      Stack Trace:
        /_/src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.cs(163,0): at System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue()
        /_/src/mono/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.Mono.cs(22,0): at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
        /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(57,0): at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

This is the source of the test failures in #94555 (comment).

cc: @radekdoulik, @tannergooding

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Repro:
#95588

        [Fact]
        public void Vector128SByteAbs_MinValue()
        {
            Vector128<sbyte> vector = Vector128.Create(sbyte.MinValue);
            Vector128<sbyte> abs = Vector128.Abs(vector);
            for (int index = 0; index < Vector128<sbyte>.Count; index++)
            {
                Assert.Equal(sbyte.MinValue, vector.GetElement(index));
            }
        }

This test passes on coreclr. On mono it fails with:

    System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue [FAIL]
      System.OverflowException : Negating the minimum value of a twos complement number is invalid.
      Stack Trace:
        /_/src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.cs(163,0): at System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue()
        /_/src/mono/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.Mono.cs(22,0): at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
        /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(57,0): at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

This is the source of the test failures in #94555 (comment).

cc: @radekdoulik, @tannergooding

Author:	stephentoub
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[lambdageek]

Self contained repro with net8.0:

using System.Runtime.Intrinsics;

Vector128<sbyte> vector = Vector128.Create(sbyte.MinValue);
var vector2 = Vector128.Abs(vector);
Console.WriteLine(vector);
Console.WriteLine(vector2);

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <PropertyGroup Condition="true">
    <UseMonoRuntime>true</UseMonoRuntime>
    <SelfContained>true</SelfContained>
  </PropertyGroup>
</Project>

This throws with both JIT and interp:

$ dotnet run

Unhandled Exception:
System.OverflowException: Negating the minimum value of a twos complement number is invalid.
   at Program.<Main>$(String[] args) in /tmp/abcd/Program.cs:line 5
[ERROR] FATAL UNHANDLED EXCEPTION: System.OverflowException: Negating the minimum value of a twos complement number is invalid.
   at Program.<Main>$(String[] args) in /tmp/abcd/Program.cs:line 5

$ MONO_ENV_OPTIONS=--interp dotnet run

Unhandled Exception:
System.OverflowException: Negating the minimum value of a twos complement number is invalid.
   at Program.<Main>$(String[] args) in /tmp/abcd/Program.cs:line 5
[ERROR] FATAL UNHANDLED EXCEPTION: System.OverflowException: Negating the minimum value of a twos complement number is invalid.
   at Program.<Main>$(String[] args) in /tmp/abcd/Program.cs:line 5

Tagging subscribers to this area: @SamMonoRT, @fanyang-mono
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Repro:
#95588

        [Fact]
        public void Vector128SByteAbs_MinValue()
        {
            Vector128<sbyte> vector = Vector128.Create(sbyte.MinValue);
            Vector128<sbyte> abs = Vector128.Abs(vector);
            for (int index = 0; index < Vector128<sbyte>.Count; index++)
            {
                Assert.Equal(sbyte.MinValue, vector.GetElement(index));
            }
        }

This test passes on coreclr. On mono it fails with:

    System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue [FAIL]
      System.OverflowException : Negating the minimum value of a twos complement number is invalid.
      Stack Trace:
        /_/src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.cs(163,0): at System.Runtime.Intrinsics.Tests.Vectors.Vector128Tests.Vector128SByteAbs_MinValue()
        /_/src/mono/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.Mono.cs(22,0): at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
        /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(57,0): at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

This is the source of the test failures in #94555 (comment).

cc: @radekdoulik, @tannergooding

Author:	stephentoub
Assignees:	-
Labels:	area-Codegen-Intrinsics-mono
Milestone:	8.0.x

[MichalPetryka]

runtime/src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Scalar.cs

Line 165 in 4ceefab

return (T)(object)Math.Abs((sbyte)(object)value);

The issue is here, the Mono JIT doesn't expand Abs for integers and uses the managed fallback which is broken so this isn't Mono specific.

[tannergooding]

This might be a bug in Scalar<T>.Abs which is used for the software fallback. Looks like its just deferring to Math.Abs which would throw for MinValue rather than returning MinValue