Merge pull request #4716 from Microsoft/optimizeFreshTypeRelation

Only obtain regular type of fresh object literal type if necessary

src/compiler/checker.ts

@@ -4640,7 +4640,9 @@ namespace ts {
                     // and intersection types are further deconstructed on the target side, we don't want to
                     // make the check again (as it might fail for a partial target type). Therefore we obtain
                     // the regular source type and proceed with that.
-                    source = getRegularTypeOfObjectLiteral(source);
+                    if (target.flags & TypeFlags.UnionOrIntersection) {
+                        source = getRegularTypeOfObjectLiteral(source);
+                    }
                 }
 
                 let saveErrorInfo = errorInfo;
@@ -5511,6 +5513,7 @@ namespace ts {
                     regularType.constructSignatures = (<ResolvedType>type).constructSignatures;
                     regularType.stringIndexType = (<ResolvedType>type).stringIndexType;
                     regularType.numberIndexType = (<ResolvedType>type).numberIndexType;
+                    (<FreshObjectLiteralType>type).regularType = regularType;
                 }
                 return regularType;
             }