reduced the size of Microsoft.CodeAnalysis.CSharp.Conversion

src/Compilers/CSharp/Portable/Binder/Binder_Conversions.cs

@@ -363,13 +363,14 @@ private BoundExpression CreateTupleLiteralConversion(CSharpSyntaxNode syntax, Bo
 
             ImmutableArray<TypeSymbol> targetElementTypes = targetType.GetElementTypesOfTupleOrCompatible();
             Debug.Assert(targetElementTypes.Length == arguments.Length, "converting a tuple literal to incompatible type?");
+            var underlyingConversions = conversionWithoutNullable.UnderlyingConversions;
 
             for (int i = 0; i < arguments.Length; i++)
             {
                 var argument = arguments[i];
                 var destType = targetElementTypes[i];
+                var elementConversion = underlyingConversions[i];
 
-                Conversion elementConversion = conversionWithoutNullable.UnderlyingConversions[i];
                 convertedArguments.Add(CreateConversion(argument.Syntax, argument, elementConversion, isCast, destType, diagnostics));
             }
 

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

@@ -6177,7 +6177,12 @@ private BoundExpression TryImplicitConversionToArrayIndex(BoundExpression expr,
                 return null;
             }
 
-            BoundExpression result = CreateConversion(expr.Syntax, expr, conversion.WithArrayIndexConversion(true), isCast: false, destination: type, diagnostics: attemptDiagnostics); // UNDONE: was cast?
+            if (conversion.IsDynamic)
+            {
+                conversion = conversion.SetArrayIndexConversionForDynamic();
+            }
+
+            BoundExpression result = CreateConversion(expr.Syntax, expr, conversion, isCast: false, destination: type, diagnostics: attemptDiagnostics); // UNDONE: was cast?
             Debug.Assert(result != null); // If this ever fails (it shouldn't), then put a null-check around the diagnostics update.
 
             diagnostics.AddRange(attemptDiagnostics);

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

@@ -337,7 +337,7 @@ private Conversion ClassifyImplicitTupleLiteralConversion(BoundTupleLiteral sour
 
                     if (underlyingTupleConversion.Exists)
                     {
-                        return new Conversion(ConversionKind.ImplicitNullable, new Conversion[] { underlyingTupleConversion });
+                        return new Conversion(ConversionKind.ImplicitNullable, ImmutableArray.Create(underlyingTupleConversion));
                     }
                 }
             }
@@ -356,7 +356,7 @@ private Conversion ClassifyExplicitTupleLiteralConversion(BoundTupleLiteral sour
             // strip nullable from the destination
             //
             // the following should work and it is an ExplicitNullable conversion
-            //    var x = ((byte, string)?)(1,2);
+            //    var x = ((byte, string)?)(1,null);
             if (destination.Kind == SymbolKind.NamedType)
             {
                 var nt = (NamedTypeSymbol)destination;
@@ -366,7 +366,7 @@ private Conversion ClassifyExplicitTupleLiteralConversion(BoundTupleLiteral sour
 
                     if (underlyingTupleConversion.Exists)
                     {
-                        return new Conversion(ConversionKind.ExplicitNullable, new Conversion[] { underlyingTupleConversion });
+                        return new Conversion(ConversionKind.ExplicitNullable, ImmutableArray.Create(underlyingTupleConversion));
                     }
                 }
             }
@@ -788,7 +788,7 @@ protected override Conversion GetImplicitTupleLiteralConversion(BoundTupleLitera
                 argumentConversions.Add(result);
             }
 
-            return new Conversion(ConversionKind.ImplicitTupleLiteral, argumentConversions.ToArrayAndFree());
+            return new Conversion(ConversionKind.ImplicitTupleLiteral, argumentConversions.ToImmutableAndFree());
         }
 
         protected override Conversion GetExplicitTupleLiteralConversion(BoundTupleLiteral source, TypeSymbol destination, ref HashSet<DiagnosticInfo> useSiteDiagnostics, bool forCast)
@@ -822,7 +822,7 @@ protected override Conversion GetExplicitTupleLiteralConversion(BoundTupleLitera
                 argumentConversions.Add(result);
             }
 
-            return new Conversion(ConversionKind.ExplicitTupleLiteral, argumentConversions.ToArrayAndFree());
+            return new Conversion(ConversionKind.ExplicitTupleLiteral, argumentConversions.ToImmutableAndFree());
         }
 
         protected override Conversion GetInterpolatedStringConversion(BoundInterpolatedString source, TypeSymbol destination, ref HashSet<DiagnosticInfo> useSiteDiagnostics)

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

@@ -965,7 +965,7 @@ private Conversion ClassifyImplicitNullableConversion(TypeSymbol source, TypeSym
             var tupleConversion = ClassifyImplicitTupleConversion(unwrappedSource, unwrappedDestination, ref useSiteDiagnostics);
             if (tupleConversion.Exists)
             {
-                return new Conversion(ConversionKind.ImplicitNullable, new Conversion[] { tupleConversion });
+                return new Conversion(ConversionKind.ImplicitNullable, ImmutableArray.Create(tupleConversion));
             }
 
             return Conversion.NoConversion;
@@ -996,7 +996,7 @@ private Conversion ClassifyImplicitTupleConversion(TypeSymbol source, TypeSymbol
                 nestedConversions.Add(conversion);
             }
 
-            return new Conversion(ConversionKind.ImplicitTuple, nestedConversions.ToArrayAndFree());
+            return new Conversion(ConversionKind.ImplicitTuple, nestedConversions.ToImmutableAndFree());
         }
 
         private Conversion ClassifyExplicitTupleConversion(TypeSymbol source, TypeSymbol destination, ref HashSet<DiagnosticInfo> useSiteDiagnostics, bool forCast)
@@ -1027,7 +1027,7 @@ private Conversion ClassifyExplicitTupleConversion(TypeSymbol source, TypeSymbol
                 nestedConversions.Add(conversion);
             }
 
-            return new Conversion(ConversionKind.ExplicitTuple, nestedConversions.ToArrayAndFree());
+            return new Conversion(ConversionKind.ExplicitTuple, nestedConversions.ToImmutableAndFree());
         }
 
         private Conversion ClassifyExplicitNullableConversion(TypeSymbol source, TypeSymbol destination, ref HashSet<DiagnosticInfo> useSiteDiagnostics, bool forCast)
@@ -1069,7 +1069,7 @@ private Conversion ClassifyExplicitNullableConversion(TypeSymbol source, TypeSym
             var tupleConversion = ClassifyExplicitTupleConversion(unwrappedSource, unwrappedDestination, ref useSiteDiagnostics, forCast);
             if (tupleConversion.Exists)
             {
-                return new Conversion(ConversionKind.ExplicitNullable, new[] {tupleConversion});
+                return new Conversion(ConversionKind.ExplicitNullable, ImmutableArray.Create(tupleConversion));
             }
 
             if (HasExplicitEnumerationConversion(unwrappedSource, unwrappedDestination))

src/Compilers/CSharp/Portable/BoundTree/BoundExpression.cs

@@ -322,11 +322,6 @@ public bool IsExtensionMethod
             get { return this.Conversion.IsExtensionMethod; }
         }
 
-        public bool IsArrayIndex
-        {
-            get { return this.Conversion.IsArrayIndex; }
-        }
-
         public MethodSymbol SymbolOpt
         {
             get { return this.Conversion.Method; }

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

@@ -1101,7 +1101,7 @@ private BoundExpression MakeLiftedUserDefinedConversionConsequence(BoundCall cal
             Debug.Assert(!method.ReturnsVoid);
             Debug.Assert(method.ParameterCount == 1);
 
-            conversion = conversion.WithConversionMethod(method);
+            conversion = conversion.SetConversionMethod(method);
 
             if (source.IsNullableType() && target.IsNullableType())
             {

src/Compilers/CSharp/Portable/Lowering/MethodToClassRewriter.cs

@@ -671,7 +671,7 @@ private BoundNode RewriteMethodGroupConversion(BoundConversion conversion)
             var conversionInfo = conversion.Conversion;
             if (conversionInfo.Method != (object)method)
             {
-                conversionInfo = conversionInfo.WithConversionMethod(method);
+                conversionInfo = conversionInfo.SetConversionMethod(method);
             }
 
             return conversion.Update(