Shared early couldContainTypeVariables check in instantiateType

Author: ahejlsberg

src/compiler/checker.ts

@@ -14102,7 +14102,7 @@ namespace ts {
         function instantiateType(type: Type, mapper: TypeMapper | undefined): Type;
         function instantiateType(type: Type | undefined, mapper: TypeMapper | undefined): Type | undefined;
         function instantiateType(type: Type | undefined, mapper: TypeMapper | undefined): Type | undefined {
-            if (!type || !mapper) {
+            if (!(type && mapper && couldContainTypeVariables(type))) {
                 return type;
             }
             if (instantiationDepth === 50 || instantiationCount >= 5000000) {
@@ -14138,37 +14138,23 @@ namespace ts {
             }
             if (flags & TypeFlags.Object) {
                 const objectFlags = (<ObjectType>type).objectFlags;
-                if (objectFlags & ObjectFlags.Anonymous) {
-                    // If the anonymous type originates in a declaration of a function, method, class, or
-                    // interface, in an object type literal, or in an object literal expression, we may need
-                    // to instantiate the type because it might reference a type parameter.
-                    return couldContainTypeVariables(type) ?
-                        getObjectTypeInstantiation(<AnonymousType>type, mapper) : type;
-                }
-                if (objectFlags & ObjectFlags.Mapped) {
-                    return getObjectTypeInstantiation(<AnonymousType>type, mapper);
-                }
-                if (objectFlags & ObjectFlags.Reference) {
-                    if ((<TypeReference>type).node) {
-                        return getObjectTypeInstantiation(<TypeReference>type, mapper);
+                if (objectFlags & (ObjectFlags.Reference | ObjectFlags.Anonymous | ObjectFlags.Mapped)) {
+                    if (objectFlags & ObjectFlags.Reference && !((<TypeReference>type).node)) {
+                        const resolvedTypeArguments = (<TypeReference>type).resolvedTypeArguments;
+                        const newTypeArguments = instantiateTypes(resolvedTypeArguments, mapper);
+                        return newTypeArguments !== resolvedTypeArguments ? createTypeReference((<TypeReference>type).target, newTypeArguments) : type;
                     }
-                    const resolvedTypeArguments = (<TypeReference>type).resolvedTypeArguments;
-                    const newTypeArguments = instantiateTypes(resolvedTypeArguments, mapper);
-                    return newTypeArguments !== resolvedTypeArguments ? createTypeReference((<TypeReference>type).target, newTypeArguments) : type;
+                    return getObjectTypeInstantiation(<TypeReference | AnonymousType | MappedType>type, mapper);
                 }
                 return type;
             }
-            if ((flags & TypeFlags.Intersection) || (flags & TypeFlags.Union && !(flags & TypeFlags.Primitive))) {
-                if (!couldContainTypeVariables(type)) {
-                    return type;
-                }
+            if (flags & TypeFlags.UnionOrIntersection) {
                 const types = (<UnionOrIntersectionType>type).types;
                 const newTypes = instantiateTypes(types, mapper);
-                return newTypes === types
-                    ? type
-                    : (flags & TypeFlags.Intersection)
-                        ? getIntersectionType(newTypes, type.aliasSymbol, instantiateTypes(type.aliasTypeArguments, mapper))
-                        : getUnionType(newTypes, UnionReduction.Literal, type.aliasSymbol, instantiateTypes(type.aliasTypeArguments, mapper));
+                return newTypes === types ? type :
+                    flags & TypeFlags.Intersection ?
+                        getIntersectionType(newTypes, type.aliasSymbol, instantiateTypes(type.aliasTypeArguments, mapper)) :
+                        getUnionType(newTypes, UnionReduction.Literal, type.aliasSymbol, instantiateTypes(type.aliasTypeArguments, mapper));
             }
             if (flags & TypeFlags.Index) {
                 return getIndexType(instantiateType((<IndexType>type).type, mapper));