Various antigen improvements

src/Antigen/Antigen/Antigen.cs

@@ -9,6 +9,7 @@
 using Utils;
 using System.Linq;
 using System.Runtime.CompilerServices;
+using Antigen.Compilation;
 using Antigen.Execution;
 using System.Reflection;
 using System.Runtime.InteropServices;
@@ -89,8 +90,15 @@ internal static int Run(AntigenRootCommand command)
                 TestCase.s_Driver = EEDriver.GetInstance(s_runOptions.CoreRun, Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "ExecutionEngine.dll"), () => EnvVarOptions.TestVars(includeOsrSwitches: PRNG.Decide(0.3), false));
                 TestCase.s_TestRunner = TestRunner.GetInstance(TestCase.s_Driver, s_runOptions.CoreRun);
 
-                // Generate vector methods
-                VectorHelpers.RecordVectorMethods();
+                // Generate vector methods. The flag must be set before recording, because the
+                // method pool is built once and reused for every test case. The pool and the
+                // compiler both read CORE_ROOT so that the API surface Antigen generates against
+                // is the same one the tests will execute against.
+                string coreRootDirectory = Path.GetDirectoryName(Path.GetFullPath(s_runOptions.CoreRun));
+                Compiler.SetReferenceDirectory(coreRootDirectory);
+                VectorHelpers.AllowFloatToIntegralReinterpret =
+                    result.GetValue(command.AllowFloatToIntegralReinterpret);
+                VectorHelpers.RecordVectorMethods(coreRootDirectory);
 
                 Parallel.For(0, 4, (p) => RunTest());
                 Console.WriteLine($"Executed {s_testId} test cases.");

src/Antigen/Antigen/Antigen.csproj

@@ -10,6 +10,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="5.3.0 " />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="10.0.8" />
+    <PackageReference Include="System.Reflection.MetadataLoadContext" Version="9.0.0" />
   </ItemGroup>
 
   <ItemGroup>

src/Antigen/Antigen/AntigenRootCommand.cs

@@ -17,6 +17,8 @@ internal sealed class AntigenRootCommand : RootCommand
             new("--NumTestCases", "-n") { Description = "Number of test cases to execute. By default, 1000." };
         public Option<int> RunDuration { get; } =
             new("--RunDuration", "-d") { Description = "Duration in minutes to run. By default until NumTestCases, but if Duration is given, will override the NumTestCases." };
+        public Option<bool> AllowFloatToIntegralReinterpret { get; } =
+            new("--AllowFloatToIntegralReinterpret") { Description = "Allow reinterpret-casting floating point vectors to integral types (for example, Vector128.AsInt32()). Can cause false positives due to differing NaN representations." };
 
         public ParseResult Result { get; private set; }
 
@@ -26,6 +28,7 @@ public AntigenRootCommand(string[] args) : base("Antigen JIT fuzzer")
             Options.Add(IssuesFolder);
             Options.Add(NumTestCases);
             Options.Add(RunDuration);
+            Options.Add(AllowFloatToIntegralReinterpret);
 
             SetAction(result =>
             {

src/Antigen/Antigen/Expressions/ConstantValue.cs

@@ -20,6 +20,13 @@ public class ConstantValue : Expression
             { "Vector4", new List<string>() { "One", "Zero", "UnitW", "UnitX", "UnitY", "UnitZ" } },
         };
 
+        // Reduce the prevelence of vector-of-floats.AllBitsSet(), as NaN's tend to pollute
+        // otherwise interesting computations
+        private const double FloatingPointAllBitsSetProbability = 0.05;
+        private const double IntegralAllBitsSetProbability = 0.5;
+
+        private static readonly List<string> s_nonNaNVectorConstants = new List<string>() { "Zero", "One", "Indices" };
+
         protected ConstantValue(Tree.ValueType valueType, string value) : base(null)
         {
             if (valueType.PrimitiveType == Primitive.Char)
@@ -87,7 +94,13 @@ public static ConstantValue GetConstantValue(Tree.ValueType literalType, IList<W
                 }
                 else
                 {
-                    constantValue += (PRNG.Decide(0.5) ? ".AllBitsSet" : ".Zero");
+                    double allBitsSetProbability = literalType.HasFloatingPointElement()
+                        ? FloatingPointAllBitsSetProbability
+                        : IntegralAllBitsSetProbability;
+
+                    constantValue += PRNG.Decide(allBitsSetProbability)
+                        ? ".AllBitsSet"
+                        : ("." + s_nonNaNVectorConstants[PRNG.Next(s_nonNaNVectorConstants.Count)]);
                 }
             }
             else if ((literalType.PrimitiveType & Primitive.Numeric) != 0)

src/Antigen/Antigen/Helpers/PreGenerated.cs

@@ -75,7 +75,20 @@ public static Statement StaticMethods
 
                 staticMethodBuilder.AppendLine("public static int Antigen() { ");
                 staticMethodBuilder.AppendLine($"new {MainClassName}().Method0();");
-                staticMethodBuilder.AppendLine("return string.Join(Environment.NewLine, toPrint).GetHashCode();");
+                staticMethodBuilder.AppendLine("return StableHash(string.Join(Environment.NewLine, toPrint));");
+                staticMethodBuilder.AppendLine("}");
+
+                // FNV-1a hash.
+                // Stable run-to-run as opposed to string.GetHashCode()
+                staticMethodBuilder.AppendLine("[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]");
+                staticMethodBuilder.AppendLine("public static int StableHash(string s) {");
+                staticMethodBuilder.AppendLine("ulong h = 14695981039346656037UL;");
+                staticMethodBuilder.AppendLine("for (int i = 0; i < s.Length; i++) {");
+                staticMethodBuilder.AppendLine("char c = s[i];");
+                staticMethodBuilder.AppendLine("h ^= (byte)c; h *= 1099511628211UL;");
+                staticMethodBuilder.AppendLine("h ^= (byte)(c >> 8); h *= 1099511628211UL;");
+                staticMethodBuilder.AppendLine("}");
+                staticMethodBuilder.AppendLine("return (int)(h ^ (h >> 32));");
                 staticMethodBuilder.AppendLine("}");
 
                 // Log method