Adding a regression test for dotnet#81585

src/tests/JIT/Regression/JitBlue/Runtime_81585/Runtime_81585.cs

@@ -0,0 +1,31 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+[module: SkipLocalsInit]
+
+class Runtime_81585
+{
+    static int Main()
+    {
+        Vector4 a = new Vector4(new Vector2(1.051f, 2.05f), 3.478f, 1.0f);
+        Vector4 b = new Vector4(new Vector3(1.051f, 2.05f, 3.478f), 0.0f);
+        b.W = 1.0f;
+
+        float actual = Vector4.Distance(a, b);
+        AssertEqual(0.0f, actual);
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static void AssertEqual(float expected, float actual)
+    {
+        if (expected != actual)
+        {
+            throw new Exception($"Expected: {expected}; Actual: {actual}");
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_81585/Runtime_81585.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <CLRTestEnvironmentVariable Include="DOTNET_JitStress" Value="1" />
+  </ItemGroup>
+</Project>