Fix minor issues

Author: maropu

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -32,7 +32,7 @@ import org.codehaus.commons.compiler.CompileException
 import org.codehaus.janino.{ByteArrayClassLoader, ClassBodyEvaluator, JaninoRuntimeException, SimpleCompiler}
 import org.codehaus.janino.util.ClassFile
 
-import org.apache.spark.{SparkContext, SparkEnv, TaskContext, TaskKilledException}
+import org.apache.spark.{SparkEnv, TaskContext, TaskKilledException}
 import org.apache.spark.executor.InputMetrics
 import org.apache.spark.internal.Logging
 import org.apache.spark.metrics.source.CodegenMetrics
@@ -1012,6 +1012,8 @@ object CodeGenerator extends Logging {
 
   /**
    * Compile the Java source code into a Java class, using Janino.
+   *
+   * @return a pair of a generated class and the max bytecode size of generated functions.
    */
   def compile(code: CodeAndComment): (GeneratedClass, Int) = try {
     cache.get(code)