Add unit test for NaN normalization in ildasm output

Co-authored-by: agocke <515774+agocke@users.noreply.github.com>

Author: Copilot

src/tests/ilasm/FloatSpecialValues/FloatSpecialValues.il

@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+.assembly extern System.Runtime { }
+.assembly FloatSpecialValues { }
+
+.class public auto ansi beforefieldinit TestFloatSpecialValues
+       extends [System.Runtime]System.Object
+{
+  // Test NaN values - these should output with normalized "// -nan" comment
+  .field public static literal float64 NaNValue = float64(0xFFF8000000000000)
+  
+  // Test infinity values for completeness
+  .field public static literal float64 PositiveInf = float64(0x7FF0000000000000)
+  .field public static literal float64 NegativeInf = float64(0xFFF0000000000000)
+  
+  // Test float32 NaN as well
+  .field public static literal float32 NaNValue32 = float32(0xFFC00000)
+  
+  .method public hidebysig specialname rtspecialname 
+          instance void  .ctor() cil managed
+  {
+    .maxstack  8
+    ldarg.0
+    call       instance void [System.Runtime]System.Object::.ctor()
+    ret
+  }
+}

src/tests/ilasm/FloatSpecialValues/FloatSpecialValuesTests.cs

@@ -0,0 +1,117 @@
+// 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.Diagnostics;
+using System.IO;
+using System.Text.RegularExpressions;
+using Xunit;
+
+public class FloatSpecialValuesTests : IDisposable
+{
+    private string _ilasmFile;
+    private string _ildasmFile;
+
+    public FloatSpecialValuesTests()
+    {
+        string coreRoot = Environment.GetEnvironmentVariable("CORE_ROOT");
+        if (string.IsNullOrWhiteSpace(coreRoot))
+        {
+            Console.WriteLine("Environment variable is not set: 'CORE_ROOT'");
+            throw new InvalidOperationException("Environment variable is not set: 'CORE_ROOT'");
+        }
+        if (!Directory.Exists(coreRoot))
+        {
+            Console.WriteLine($"Did not find CORE_ROOT directory: {coreRoot}");
+            throw new InvalidOperationException("Did not find CORE_ROOT directory");
+        }
+
+        var nativeExeExtensions = new string[] { string.Empty, ".exe" };
+        bool found = false;
+        string ilasmFile = null;
+        string ildasmFile = null;
+        foreach (string nativeExeExtension in nativeExeExtensions)
+        {
+            ilasmFile = Path.Combine(coreRoot, $"ilasm{nativeExeExtension}");
+            ildasmFile = Path.Combine(coreRoot, $"ildasm{nativeExeExtension}");
+            if (File.Exists(ilasmFile) && File.Exists(ildasmFile))
+            {
+                found = true;
+                break;
+            }
+        }
+        if (!found)
+        {
+            Console.WriteLine($"Did not find ilasm or ildasm in CORE_ROOT directory: {coreRoot}");
+            throw new InvalidOperationException("Did not find ilasm or ildasm in CORE_ROOT directory");
+        }
+
+        _ilasmFile = ilasmFile;
+        _ildasmFile = ildasmFile;
+    }
+
+    [Fact]
+    public void NaNOutputIsNormalizedAcrossPlatforms()
+    {
+        Console.WriteLine("NaNOutputIsNormalizedAcrossPlatforms");
+
+        string ilFileName = "FloatSpecialValues.il";
+        string disasmIlFileName;
+        ProcessStartInfo ilasmPsi, ildasmPsi;
+        GetIlasmProcessStartInfos(_ilasmFile, _ildasmFile, ilFileName, out disasmIlFileName, out ilasmPsi, out ildasmPsi);
+
+        Process ilasmProcess = Process.Start(ilasmPsi);
+        ilasmProcess.WaitForExit();
+        Assert.Equal(0, ilasmProcess.ExitCode);
+
+        Process ildasmProcess = Process.Start(ildasmPsi);
+        ildasmProcess.WaitForExit();
+        Assert.Equal(0, ildasmProcess.ExitCode);
+
+        string disasmIl = File.ReadAllText(disasmIlFileName);
+
+        // Verify that NaN values use the normalized format without platform-specific suffixes
+        // The hex representation should be followed by "// -nan" without "(ind)" suffix
+        var nanFloat64Regex = new Regex(@"float64\(0xFFF8000000000000\)\s+//\s+-nan\s", RegexOptions.Compiled);
+        Assert.True(nanFloat64Regex.IsMatch(disasmIl), 
+            "NaN float64 should be output as '// -nan' without platform-specific suffixes like '(ind)'");
+
+        // Verify the output does NOT contain the Windows-specific "(ind)" suffix
+        Assert.DoesNotContain("-nan(ind)", disasmIl);
+        Assert.DoesNotContain("-nan(", disasmIl);
+    }
+
+    private static void GetIlasmProcessStartInfos(
+        string ilasmFile,
+        string ildasmFile,
+        string ilFileName,
+        out string disasmIlFileName,
+        out ProcessStartInfo ilasmPsi,
+        out ProcessStartInfo ildasmPsi)
+    {
+        if (!File.Exists(ilFileName))
+        {
+            throw new FileNotFoundException(
+                $"Did not find '{ilFileName}' in working directory '{Environment.CurrentDirectory}'");
+        }
+
+        string currentDirectory = Environment.CurrentDirectory;
+
+        ilasmPsi = new ProcessStartInfo();
+        ilasmPsi.UseShellExecute = false;
+        ilasmPsi.WorkingDirectory = currentDirectory;
+        ilasmPsi.FileName = ilasmFile;
+        string asmDllFileName = $"{Path.GetFileNameWithoutExtension(ilFileName)}.dll";
+        ilasmPsi.Arguments =
+            $"-nologo -dll -optimize -output={asmDllFileName} {ilFileName}";
+
+        ildasmPsi = new ProcessStartInfo();
+        ildasmPsi.UseShellExecute = false;
+        ildasmPsi.WorkingDirectory = currentDirectory;
+        ildasmPsi.FileName = ildasmFile;
+        disasmIlFileName = $"{Path.GetFileNameWithoutExtension(ilFileName)}_dis{Path.GetExtension(ilFileName)}";
+        ildasmPsi.Arguments = $"-out={disasmIlFileName} {asmDllFileName}";
+    }
+
+    public void Dispose() {}
+}

src/tests/ilasm/ilasm_tests.csproj

@@ -13,6 +13,7 @@
     <Compile Include="PortablePdb\IlasmPortablePdbTesterCommon.cs" />
     <Compile Include="PortablePdb\IlasmPortablePdbTesterTypes.cs" />
     <Compile Include="MethodImplOptions\MethodImplOptionsTests.cs" />
+    <Compile Include="FloatSpecialValues\FloatSpecialValuesTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <Compile Remove="PortablePdb\Resources\**" />
@@ -68,6 +69,10 @@
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
       <Link>%(Filename).il</Link>
     </None>
+    <None Include="FloatSpecialValues/*.il">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      <Link>%(Filename).il</Link>
+    </None>
   </ItemGroup>
   <Import Project="$(TestSourceDir)MergedTestRunner.targets" />
 </Project>