[SPARK-13147] [SQL] improve readability of generated code

1. try to avoid the suffix (unique id)
2. remove the comment if there is no code generated.
3. re-arrange the order of functions
4. trop the new line for inlined blocks.

Author: Davies Liu <davies@databricks.com>

Closes #11032 from davies/better_suffix.

7 files changed, 63 insertions, 39 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
index 353fb92581..c73b2f8f2a 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
@@ -103,8 +103,12 @@ abstract class Expression extends TreeNode[Expression] {
       val value = ctx.freshName("value")
       val ve = ExprCode("", isNull, value)
       ve.code = genCode(ctx, ve)
-      // Add `this` in the comment.
-      ve.copy(s"/* ${this.toCommentSafeString} */\n" + ve.code.trim)
+      if (ve.code != "") {
+        // Add `this` in the comment.
+        ve.copy(s"/* ${this.toCommentSafeString} */\n" + ve.code.trim)
+      } else {
+        ve
+      }
     }
   }
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala
index a30aba1617..63e19564dd 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala
@@ -156,7 +156,11 @@ class CodegenContext {
   /** The variable name of the input row in generated code. */
   final var INPUT_ROW = "i"
 
-  private val curId = new java.util.concurrent.atomic.AtomicInteger()
+  /**
+    * The map from a variable name to it's next ID.
+    */
+  private val freshNameIds = new mutable.HashMap[String, Int]
+  freshNameIds += INPUT_ROW -> 1
 
   /**
     * A prefix used to generate fresh name.
@@ -164,16 +168,21 @@ class CodegenContext {
   var freshNamePrefix = ""
 
   /**
-   * Returns a term name that is unique within this instance of a `CodeGenerator`.
-   *
-   * (Since we aren't in a macro context we do not seem to have access to the built in `freshName`
-   * function.)
+   * Returns a term name that is unique within this instance of a `CodegenContext`.
    */
-  def freshName(name: String): String = {
-    if (freshNamePrefix == "") {
-      s"$name${curId.getAndIncrement}"
+  def freshName(name: String): String = synchronized {
+    val fullName = if (freshNamePrefix == "") {
+      name
+    } else {
+      s"${freshNamePrefix}_$name"
+    }
+    if (freshNameIds.contains(fullName)) {
+      val id = freshNameIds(fullName)
+      freshNameIds(fullName) = id + 1
+      s"$fullName$id"
     } else {
-      s"${freshNamePrefix}_$name${curId.getAndIncrement}"
+      freshNameIds += fullName -> 1
+      fullName
     }
   }
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala
index 9f2f82d68c..6b24fae9f3 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeExtractors.scala
@@ -173,22 +173,26 @@ case class GetArrayStructFields(
   override def genCode(ctx: CodegenContext, ev: ExprCode): String = {
     val arrayClass = classOf[GenericArrayData].getName
     nullSafeCodeGen(ctx, ev, eval => {
+      val n = ctx.freshName("n")
+      val values = ctx.freshName("values")
+      val j = ctx.freshName("j")
+      val row = ctx.freshName("row")
       s"""
-        final int n = $eval.numElements();
-        final Object[] values = new Object[n];
-        for (int j = 0; j < n; j++) {
-          if ($eval.isNullAt(j)) {
-            values[j] = null;
+        final int $n = $eval.numElements();
+        final Object[] $values = new Object[$n];
+        for (int $j = 0; $j < $n; $j++) {
+          if ($eval.isNullAt($j)) {
+            $values[$j] = null;
           } else {
-            final InternalRow row = $eval.getStruct(j, $numFields);
-            if (row.isNullAt($ordinal)) {
-              values[j] = null;
+            final InternalRow $row = $eval.getStruct($j, $numFields);
+            if ($row.isNullAt($ordinal)) {
+              $values[$j] = null;
             } else {
-              values[j] = ${ctx.getValue("row", field.dataType, ordinal.toString)};
+              $values[$j] = ${ctx.getValue(row, field.dataType, ordinal.toString)};
             }
           }
         }
-        ${ev.value} = new $arrayClass(values);
+        ${ev.value} = new $arrayClass($values);
       """
     })
   }
@@ -227,12 +231,13 @@ case class GetArrayItem(child: Expression, ordinal: Expression)
 
   override def genCode(ctx: CodegenContext, ev: ExprCode): String = {
     nullSafeCodeGen(ctx, ev, (eval1, eval2) => {
+      val index = ctx.freshName("index")
       s"""
-        final int index = (int) $eval2;
-        if (index >= $eval1.numElements() || index < 0 || $eval1.isNullAt(index)) {
+        final int $index = (int) $eval2;
+        if ($index >= $eval1.numElements() || $index < 0 || $eval1.isNullAt($index)) {
           ${ev.isNull} = true;
         } else {
-          ${ev.value} = ${ctx.getValue(eval1, dataType, "index")};
+          ${ev.value} = ${ctx.getValue(eval1, dataType, index)};
         }
       """
     })
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala
index 02b0f423ed..1475496907 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala
@@ -170,8 +170,8 @@ case class InputAdapter(child: SparkPlan) extends LeafNode with CodegenSupport {
     s"""
        | while (input.hasNext()) {
        |   InternalRow $row = (InternalRow) input.next();
-       |   ${columns.map(_.code).mkString("\n")}
-       |   ${consume(ctx, columns)}
+       |   ${columns.map(_.code).mkString("\n").trim}
+       |   ${consume(ctx, columns).trim}
        | }
      """.stripMargin
   }
@@ -236,15 +236,16 @@ case class WholeStageCodegen(plan: CodegenSupport, children: Seq[SparkPlan])
 
         private Object[] references;
         ${ctx.declareMutableStates()}
-        ${ctx.declareAddedFunctions()}
 
         public GeneratedIterator(Object[] references) {
-         this.references = references;
-         ${ctx.initMutableStates()}
+          this.references = references;
+          ${ctx.initMutableStates()}
         }
 
+        ${ctx.declareAddedFunctions()}
+
         protected void processNext() throws java.io.IOException {
-         $code
+          ${code.trim}
         }
       }
       """
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregate.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregate.scala
index f61db8594d..d024477061 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregate.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/TungstenAggregate.scala
@@ -211,9 +211,9 @@ case class TungstenAggregate(
        |   $doAgg();
        |
        |   // output the result
-       |   $genResult
+       |   ${genResult.trim}
        |
-       |   ${consume(ctx, resultVars)}
+       |   ${consume(ctx, resultVars).trim}
        | }
      """.stripMargin
   }
@@ -242,9 +242,9 @@ case class TungstenAggregate(
     }
     s"""
        | // do aggregate
-       | ${aggVals.map(_.code).mkString("\n")}
+       | ${aggVals.map(_.code).mkString("\n").trim}
        | // update aggregation buffer
-       | ${updates.mkString("")}
+       | ${updates.mkString("\n").trim}
      """.stripMargin
   }
 
@@ -523,7 +523,7 @@ case class TungstenAggregate(
     // Finally, sort the spilled aggregate buffers by key, and merge them together for same key.
     s"""
      // generate grouping key
-     ${keyCode.code}
+     ${keyCode.code.trim}
      UnsafeRow $buffer = null;
      if ($checkFallback) {
        // try to get the buffer from hash map
@@ -547,9 +547,9 @@ case class TungstenAggregate(
      $incCounter
 
      // evaluate aggregate function
-     ${evals.map(_.code).mkString("\n")}
+     ${evals.map(_.code).mkString("\n").trim}
      // update aggregate buffer
-     ${updates.mkString("\n")}
+     ${updates.mkString("\n").trim}
      """
   }
 
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala
index fd81531c93..ae4422195c 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala
@@ -93,9 +93,14 @@ case class Filter(condition: Expression, child: SparkPlan) extends UnaryNode wit
       BindReferences.bindReference(condition, child.output))
     ctx.currentVars = input
     val eval = expr.gen(ctx)
+    val nullCheck = if (expr.nullable) {
+      s"!${eval.isNull} &&"
+    } else {
+      s""
+    }
     s"""
        | ${eval.code}
-       | if (!${eval.isNull} && ${eval.value}) {
+       | if ($nullCheck ${eval.value}) {
        |   ${consume(ctx, ctx.currentVars)}
        | }
      """.stripMargin
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/BenchmarkWholeStageCodegen.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/BenchmarkWholeStageCodegen.scala
index 1ccf0e3d06..ec2b9ab2cb 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/BenchmarkWholeStageCodegen.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/BenchmarkWholeStageCodegen.scala
@@ -199,7 +199,7 @@ class BenchmarkWholeStageCodegen extends SparkFunSuite {
   // These benchmark are skipped in normal build
   ignore("benchmark") {
     // testWholeStage(200 << 20)
-    // testStddev(20 << 20)
+    // testStatFunctions(20 << 20)
     // testAggregateWithKey(20 << 20)
     // testBytesToBytesMap(1024 * 1024 * 50)
   }