Reduce TypeConversions allocations by caching them in AssemblySymbol

src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/ConversionsBase.cs

@@ -35,6 +35,7 @@ protected ConversionsBase(AssemblySymbol corLibrary, int currentRecursionDepth,
             Debug.Assert((object)corLibrary != null);
             Debug.Assert(otherNullabilityOpt == null || includeNullability != otherNullabilityOpt.IncludeNullability);
             Debug.Assert(otherNullabilityOpt == null || currentRecursionDepth == otherNullabilityOpt.currentRecursionDepth);
+            Debug.Assert(corLibrary == corLibrary.CorLibrary);
 
             this.corLibrary = corLibrary;
             this.currentRecursionDepth = currentRecursionDepth;

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.UsingsFromOptionsAndDiagnostics.cs

@@ -134,7 +134,7 @@ private void Validate(CSharpCompilation compilation)
                 Debug.Assert(diagnostics.DependenciesBag is object);
 
                 var corLibrary = compilation.SourceAssembly.CorLibrary;
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 foreach (var @using in UsingNamespacesOrTypes)
                 {
                     diagnostics.Clear();

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_ForEachStatement.cs

@@ -299,7 +299,7 @@ private BoundStatement WrapWithTryFinallyDispose(
 
                 idisposableTypeSymbol = disposeMethod.ContainingType;
                 Debug.Assert(_factory.CurrentFunction is { });
-                var conversions = new TypeConversions(_factory.CurrentFunction.ContainingAssembly.CorLibrary);
+                var conversions = _factory.CurrentFunction.ContainingAssembly.CorLibrary.TypeConversions;
 
                 CompoundUseSiteInfo<AssemblySymbol> useSiteInfo = GetNewCompoundUseSiteInfo();
                 isImplicit = conversions.ClassifyImplicitConversionFromType(enumeratorType, idisposableTypeSymbol, ref useSiteInfo).IsImplicit;

src/Compilers/CSharp/Portable/Symbols/AliasSymbol.cs

@@ -235,7 +235,7 @@ internal void CheckConstraints(BindingDiagnosticBag diagnostics)
             if ((object?)target != null && Locations.Length > 0)
             {
                 var corLibrary = this.ContainingAssembly.CorLibrary;
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 target.CheckAllConstraints(DeclaringCompilation, conversions, GetFirstLocation(), diagnostics);
             }
         }

src/Compilers/CSharp/Portable/Symbols/AssemblySymbol.cs

@@ -53,6 +53,8 @@ internal AssemblySymbol CorLibrary
             }
         }
 
+        internal abstract TypeConversions TypeConversions { get; }
+
         /// <summary>
         /// A helper method for ReferenceManager to set the system assembly, which provides primitive 
         /// types like Object, String, etc., e.g. mscorlib.dll. 

src/Compilers/CSharp/Portable/Symbols/ConstraintsHelper.cs

@@ -123,7 +123,7 @@ public static TypeParameterBounds ResolveBounds(
             {
                 var constraintTypesBuilder = ArrayBuilder<TypeWithAnnotations>.GetInstance();
                 var interfacesBuilder = ArrayBuilder<NamedTypeSymbol>.GetInstance();
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 var useSiteInfo = new CompoundUseSiteInfo<AssemblySymbol>(template);
 
                 // Resolve base types, determine the effective base class and

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEParameterSymbol.cs

@@ -673,7 +673,7 @@ internal override bool IsCallerLineNumber
                 {
                     var discardedUseSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
                     bool isCallerLineNumber = HasCallerLineNumberAttribute
-                        && new TypeConversions(ContainingAssembly).HasCallerLineNumberConversion(this.Type, ref discardedUseSiteInfo);
+                        && ContainingAssembly.TypeConversions.HasCallerLineNumberConversion(this.Type, ref discardedUseSiteInfo);
 
                     value = _packedFlags.SetWellKnownAttribute(flag, isCallerLineNumber);
                 }
@@ -693,7 +693,7 @@ internal override bool IsCallerFilePath
                     var discardedUseSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
                     bool isCallerFilePath = !HasCallerLineNumberAttribute
                         && HasCallerFilePathAttribute
-                        && new TypeConversions(ContainingAssembly).HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
+                        && ContainingAssembly.TypeConversions.HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
 
                     value = _packedFlags.SetWellKnownAttribute(flag, isCallerFilePath);
                 }
@@ -714,7 +714,7 @@ internal override bool IsCallerMemberName
                     bool isCallerMemberName = !HasCallerLineNumberAttribute
                         && !HasCallerFilePathAttribute
                         && HasCallerMemberNameAttribute
-                        && new TypeConversions(ContainingAssembly).HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
+                        && ContainingAssembly.TypeConversions.HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
 
                     value = _packedFlags.SetWellKnownAttribute(flag, isCallerMemberName);
                 }
@@ -737,7 +737,7 @@ internal override int CallerArgumentExpressionParameterIndex
                     && !HasCallerLineNumberAttribute
                     && !HasCallerFilePathAttribute
                     && !HasCallerMemberNameAttribute
-                    && new TypeConversions(ContainingAssembly).HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
+                    && ContainingAssembly.TypeConversions.HasCallerInfoStringConversion(this.Type, ref discardedUseSiteInfo);
 
                 if (isCallerArgumentExpression)
                 {

src/Compilers/CSharp/Portable/Symbols/MetadataOrSourceAssemblySymbol.cs

@@ -26,6 +26,8 @@ internal abstract class MetadataOrSourceAssemblySymbol
         /// </summary>
         private NamedTypeSymbol[] _lazySpecialTypes;
 
+        private TypeConversions _lazyTypeConversions;
+
         /// <summary>
         /// How many Cor types have we cached so far.
         /// </summary>
@@ -273,6 +275,24 @@ private ConcurrentDictionary<AssemblySymbol, IVTConclusion> AssembliesToWhichInt
             }
         }
 
+        internal sealed override TypeConversions TypeConversions
+        {
+            get
+            {
+                if (this != CorLibrary)
+                {
+                    return CorLibrary.TypeConversions;
+                }
+
+                if (_lazyTypeConversions is null)
+                {
+                    Interlocked.CompareExchange(ref _lazyTypeConversions, new TypeConversions(this), null);
+                }
+
+                return _lazyTypeConversions;
+            }
+        }
+
         internal virtual bool IsNetModule() => false;
     }
 }

src/Compilers/CSharp/Portable/Symbols/MissingAssemblySymbol.cs

@@ -203,6 +203,8 @@ public override bool MightContainExtensionMethods
             }
         }
 
+        internal override TypeConversions TypeConversions => CorLibrary.TypeConversions;
+
         public override AssemblyMetadata GetMetadata() => null;
 
         internal sealed override IEnumerable<NamedTypeSymbol> GetAllTopLevelForwardedTypes()

src/Compilers/CSharp/Portable/Symbols/MissingCorLibrarySymbol.cs

@@ -29,12 +29,29 @@ internal sealed class MissingCorLibrarySymbol : MissingAssemblySymbol
         /// <remarks></remarks>
         private NamedTypeSymbol[] _lazySpecialTypes;
 
+        private TypeConversions _lazyTypeConversions;
+
         private MissingCorLibrarySymbol()
             : base(new AssemblyIdentity("<Missing Core Assembly>"))
         {
             this.SetCorLibrary(this);
         }
 
+        internal override TypeConversions TypeConversions
+        {
+            get
+            {
+                Debug.Assert(this == CorLibrary);
+
+                if (_lazyTypeConversions is null)
+                {
+                    Interlocked.CompareExchange(ref _lazyTypeConversions, new TypeConversions(this), null);
+                }
+
+                return _lazyTypeConversions;
+            }
+        }
+
         /// <summary>
         /// Lookup declaration for predefined CorLib type in this Assembly. Only should be
         /// called if it is know that this is the Cor Library (mscorlib).

src/Compilers/CSharp/Portable/Symbols/ReducedExtensionMethodSymbol.cs

@@ -48,7 +48,7 @@ public static MethodSymbol Create(MethodSymbol method, TypeSymbol receiverType,
                 return null;
             }
 
-            var conversions = new TypeConversions(method.ContainingAssembly.CorLibrary);
+            var conversions = method.ContainingAssembly.CorLibrary.TypeConversions;
             var conversion = conversions.ConvertExtensionMethodThisArg(method.Parameters[0].Type, receiverType, ref useSiteInfo);
             if (!conversion.Exists)
             {
@@ -127,7 +127,7 @@ private static MethodSymbol InferExtensionMethodTypeArguments(MethodSymbol metho
 
             var containingAssembly = method.ContainingAssembly;
             var errorNamespace = containingAssembly.GlobalNamespace;
-            var conversions = new TypeConversions(containingAssembly.CorLibrary);
+            var conversions = containingAssembly.CorLibrary.TypeConversions;
 
             // There is absolutely no plausible syntax/tree that we could use for these
             // synthesized literals.  We could be speculatively binding a call to a PE method.

src/Compilers/CSharp/Portable/Symbols/Retargeting/RetargetingAssemblySymbol.cs

@@ -278,6 +278,8 @@ public override bool MightContainExtensionMethods
             get { return null; }
         }
 
+        internal override TypeConversions TypeConversions => CorLibrary.TypeConversions;
+
         internal override bool GetGuidString(out string guidString)
         {
             return _underlyingAssembly.GetGuidString(out guidString);

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol.cs

@@ -2225,7 +2225,7 @@ private void CheckIndexerSignatureCollisions(
 
         private void CheckSpecialMemberErrors(BindingDiagnosticBag diagnostics)
         {
-            var conversions = new TypeConversions(this.ContainingAssembly.CorLibrary);
+            var conversions = this.ContainingAssembly.CorLibrary.TypeConversions;
             foreach (var member in this.GetMembersUnordered())
             {
                 member.AfterAddingTypeMembersChecks(conversions, diagnostics);

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamedTypeSymbol_Bases.cs

@@ -113,7 +113,7 @@ protected override void CheckBase(BindingDiagnosticBag diagnostics)
             if (singleDeclaration != null)
             {
                 var corLibrary = this.ContainingAssembly.CorLibrary;
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 var location = singleDeclaration.NameLocation;
 
                 localBase.CheckAllConstraints(DeclaringCompilation, conversions, location, diagnostics);
@@ -159,7 +159,7 @@ protected override void CheckInterfaces(BindingDiagnosticBag diagnostics)
             if (singleDeclaration != null)
             {
                 var corLibrary = this.ContainingAssembly.CorLibrary;
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 var location = singleDeclaration.NameLocation;
 
                 foreach (var pair in interfaces)

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamespaceSymbol.AliasesAndUsings.cs

@@ -997,7 +997,7 @@ private static void Validate(SourceNamespaceSymbol declaringSymbol, SyntaxRefere
                 }
 
                 var corLibrary = compilation.SourceAssembly.CorLibrary;
-                var conversions = new TypeConversions(corLibrary);
+                var conversions = corLibrary.TypeConversions;
                 foreach (var @using in usingsAndDiagnostics.UsingNamespacesOrTypes)
                 {
                     if (@using.UsingDirectiveReference!.SyntaxTree != declarationSyntax.SyntaxTree)

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertySymbolBase.cs

@@ -1460,7 +1460,7 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
                                 if (parameters.Length > 0)
                                 {
                                     var diagnostics = BindingDiagnosticBag.GetInstance();
-                                    var conversions = new TypeConversions(this.ContainingAssembly.CorLibrary);
+                                    var conversions = this.ContainingAssembly.CorLibrary.TypeConversions;
                                     foreach (var parameter in this.Parameters)
                                     {
                                         parameter.ForceComplete(locationOpt, cancellationToken);
@@ -1489,7 +1489,7 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
                             if (_state.NotePartComplete(CompletionPart.StartPropertyType))
                             {
                                 var diagnostics = BindingDiagnosticBag.GetInstance();
-                                var conversions = new TypeConversions(this.ContainingAssembly.CorLibrary);
+                                var conversions = this.ContainingAssembly.CorLibrary.TypeConversions;
                                 this.Type.CheckAllConstraints(DeclaringCompilation, conversions, Location, diagnostics);
 
                                 ValidatePropertyType(diagnostics);

src/Compilers/CSharp/Portable/Symbols/Source/SourceTypeParameterSymbol.cs

@@ -259,7 +259,7 @@ private void CheckConstraintTypeConstraints(BindingDiagnosticBag diagnostics)
             }
 
             var args = ConstraintsHelper.CheckConstraintsArgsBoxed.Allocate(
-                DeclaringCompilation, new TypeConversions(ContainingAssembly.CorLibrary), _locations[0], diagnostics);
+                DeclaringCompilation, ContainingAssembly.CorLibrary.TypeConversions, _locations[0], diagnostics);
             foreach (var constraintType in constraintTypes)
             {
                 if (!diagnostics.ReportUseSite(constraintType.Type, args.Args.Location))

src/Compilers/CSharp/Test/Symbol/Symbols/MockAssemblySymbol.cs

@@ -35,6 +35,11 @@ internal override ImmutableArray<byte> PublicKey
             get { throw new NotImplementedException(); }
         }
 
+        internal override TypeConversions TypeConversions
+        {
+            get { throw new NotImplementedException(); }
+        }
+
         public override ImmutableArray<ModuleSymbol> Modules
         {
             get { return ImmutableArray.Create<ModuleSymbol>(); }