[SPARK-18091][SQL] Deep if expressions cause Generated SpecificUnsafeProjection code to exceed JVM code size limit

## What changes were proposed in this pull request?

Fix for SPARK-18091 which is a bug related to large if expressions causing generated SpecificUnsafeProjection code to exceed JVM code size limit.

This PR changes if expression's code generation to place its predicate, true value and false value expressions' generated code in separate methods in context so as to never generate too long combined code.
## How was this patch tested?

Added a unit test and also tested manually with the application (having transformations similar to the unit test) which caused the issue to be identified in the first place.

Author: Kapil Singh <[email protected]>

Closes #15620 from kapilsingh5050/SPARK-18091-IfCodegenFix.

Author: Kapil Singh

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala

@@ -64,19 +64,75 @@ case class If(predicate: Expression, trueValue: Expression, falseValue: Expressi
     val trueEval = trueValue.genCode(ctx)
     val falseEval = falseValue.genCode(ctx)
 
-    ev.copy(code = s"""
-      ${condEval.code}
-      boolean ${ev.isNull} = false;
-      ${ctx.javaType(dataType)} ${ev.value} = ${ctx.defaultValue(dataType)};
-      if (!${condEval.isNull} && ${condEval.value}) {
-        ${trueEval.code}
-        ${ev.isNull} = ${trueEval.isNull};
-        ${ev.value} = ${trueEval.value};
-      } else {
-        ${falseEval.code}
-        ${ev.isNull} = ${falseEval.isNull};
-        ${ev.value} = ${falseEval.value};
-      }""")
+    // place generated code of condition, true value and false value in separate methods if
+    // their code combined is large
+    val combinedLength = condEval.code.length + trueEval.code.length + falseEval.code.length
+    val generatedCode = if (combinedLength > 1024 &&
+      // Split these expressions only if they are created from a row object
+      (ctx.INPUT_ROW != null && ctx.currentVars == null)) {
+
+      val (condFuncName, condGlobalIsNull, condGlobalValue) =
+        createAndAddFunction(ctx, condEval, predicate.dataType, "evalIfCondExpr")
+      val (trueFuncName, trueGlobalIsNull, trueGlobalValue) =
+        createAndAddFunction(ctx, trueEval, trueValue.dataType, "evalIfTrueExpr")
+      val (falseFuncName, falseGlobalIsNull, falseGlobalValue) =
+        createAndAddFunction(ctx, falseEval, falseValue.dataType, "evalIfFalseExpr")
+      s"""
+        $condFuncName(${ctx.INPUT_ROW});
+        boolean ${ev.isNull} = false;
+        ${ctx.javaType(dataType)} ${ev.value} = ${ctx.defaultValue(dataType)};
+        if (!$condGlobalIsNull && $condGlobalValue) {
+          $trueFuncName(${ctx.INPUT_ROW});
+          ${ev.isNull} = $trueGlobalIsNull;
+          ${ev.value} = $trueGlobalValue;
+        } else {
+          $falseFuncName(${ctx.INPUT_ROW});
+          ${ev.isNull} = $falseGlobalIsNull;
+          ${ev.value} = $falseGlobalValue;
+        }
+      """
+    }
+    else {
+      s"""
+        ${condEval.code}
+        boolean ${ev.isNull} = false;
+        ${ctx.javaType(dataType)} ${ev.value} = ${ctx.defaultValue(dataType)};
+        if (!${condEval.isNull} && ${condEval.value}) {
+          ${trueEval.code}
+          ${ev.isNull} = ${trueEval.isNull};
+          ${ev.value} = ${trueEval.value};
+        } else {
+          ${falseEval.code}
+          ${ev.isNull} = ${falseEval.isNull};
+          ${ev.value} = ${falseEval.value};
+        }
+      """
+    }
+
+    ev.copy(code = generatedCode)
+  }
+
+  private def createAndAddFunction(
+      ctx: CodegenContext,
+      ev: ExprCode,
+      dataType: DataType,
+      baseFuncName: String): (String, String, String) = {
+    val globalIsNull = ctx.freshName("isNull")
+    ctx.addMutableState("boolean", globalIsNull, s"$globalIsNull = false;")
+    val globalValue = ctx.freshName("value")
+    ctx.addMutableState(ctx.javaType(dataType), globalValue,
+      s"$globalValue = ${ctx.defaultValue(dataType)};")
+    val funcName = ctx.freshName(baseFuncName)
+    val funcBody =
+      s"""
+         |private void $funcName(InternalRow ${ctx.INPUT_ROW}) {
+         |  ${ev.code.trim}
+         |  $globalIsNull = ${ev.isNull};
+         |  $globalValue = ${ev.value};
+         |}
+         """.stripMargin
+    ctx.addNewFunction(funcName, funcBody)
+    (funcName, globalIsNull, globalValue)
   }
 
   override def toString: String = s"if ($predicate) $trueValue else $falseValue"

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CodeGenerationSuite.scala

@@ -97,6 +97,27 @@ class CodeGenerationSuite extends SparkFunSuite with ExpressionEvalHelper {
     assert(actual(0) == cases)
   }
 
+  test("SPARK-18091: split large if expressions into blocks due to JVM code size limit") {
+    val inStr = "StringForTesting"
+    val row = create_row(inStr)
+    val inputStrAttr = 'a.string.at(0)
+
+    var strExpr: Expression = inputStrAttr
+    for (_ <- 1 to 13) {
+      strExpr = If(EqualTo(Decode(Encode(strExpr, "utf-8"), "utf-8"), inputStrAttr),
+        strExpr, strExpr)
+    }
+
+    val expressions = Seq(strExpr)
+    val plan = GenerateUnsafeProjection.generate(expressions, true)
+    val actual = plan(row).toSeq(expressions.map(_.dataType))
+    val expected = Seq(UTF8String.fromString(inStr))
+
+    if (!checkResult(actual, expected)) {
+      fail(s"Incorrect Evaluation: expressions: $expressions, actual: $actual, expected: $expected")
+    }
+  }
+
   test("SPARK-14793: split wide array creation into blocks due to JVM code size limit") {
     val length = 5000
     val expressions = Seq(CreateArray(List.fill(length)(EqualTo(Literal(1), Literal(1)))))