[SPARK-8680] [SQL] Slightly improve PropagateTypes

JIRA: https://issues.apache.org/jira/browse/SPARK-8680

This PR slightly improve `PropagateTypes` in `HiveTypeCoercion`. It moves `q.inputSet` outside `q transformExpressions` instead calling `inputSet` multiple times. It also builds a map of attributes for looking attribute easily.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #7087 from viirya/improve_propagatetypes and squashes the following commits:

5c314c1 [Liang-Chi Hsieh] For comments.
913f6ad [Liang-Chi Hsieh] Slightly improve PropagateTypes.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala

@@ -131,20 +131,22 @@ trait HiveTypeCoercion {
       // Don't propagate types from unresolved children.
       case q: LogicalPlan if !q.childrenResolved => q
 
-      case q: LogicalPlan => q transformExpressions {
-        case a: AttributeReference =>
-          q.inputSet.find(_.exprId == a.exprId) match {
-            // This can happen when a Attribute reference is born in a non-leaf node, for example
-            // due to a call to an external script like in the Transform operator.
-            // TODO: Perhaps those should actually be aliases?
-            case None => a
-            // Leave the same if the dataTypes match.
-            case Some(newType) if a.dataType == newType.dataType => a
-            case Some(newType) =>
-              logDebug(s"Promoting $a to $newType in ${q.simpleString}}")
-              newType
-          }
-      }
+      case q: LogicalPlan =>
+        val inputMap = q.inputSet.toSeq.map(a => (a.exprId, a)).toMap
+        q transformExpressions {
+          case a: AttributeReference =>
+            inputMap.get(a.exprId) match {
+              // This can happen when a Attribute reference is born in a non-leaf node, for example
+              // due to a call to an external script like in the Transform operator.
+              // TODO: Perhaps those should actually be aliases?
+              case None => a
+              // Leave the same if the dataTypes match.
+              case Some(newType) if a.dataType == newType.dataType => a
+              case Some(newType) =>
+                logDebug(s"Promoting $a to $newType in ${q.simpleString}}")
+                newType
+            }
+        }
     }
   }