Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/19813#discussion_r155537400
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/ExpressionCodegen.scala
---
@@ -0,0 +1,237 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions.codegen
+
+import scala.collection.mutable
+
+import org.apache.spark.sql.catalyst.expressions._
+
+/**
+ * Defines util methods used in expression code generation.
+ */
+object ExpressionCodegen {
+
+ /**
+ * Given an expression, returns the all necessary parameters to evaluate
it, so the generated
+ * code of this expression can be split in a function.
+ * The 1st string in returned tuple is the parameter strings used to
call the function.
+ * The 2nd string in returned tuple is the parameter strings used to
declare the function.
+ *
+ * Returns `None` if it can't produce valid parameters.
+ *
+ * Params to include:
+ * 1. Evaluated columns referred by this, children or deferred
expressions.
+ * 2. Rows referred by this, children or deferred expressions.
+ * 3. Eliminated subexpressions referred bu children expressions.
+ */
+ def getExpressionInputParams(
+ ctx: CodegenContext,
+ expr: Expression): Option[(Seq[String], Seq[String])] = {
+ val (inputAttrs, inputVars) = getInputVarsForChildren(ctx, expr)
+ val paramsFromColumns = prepareFunctionParams(ctx, inputAttrs,
inputVars)
+
+ val subExprs = getSubExprInChildren(ctx, expr)
+ val subExprCodes = getSubExprCodes(ctx, subExprs)
+ val paramsFromSubExprs = prepareFunctionParams(ctx, subExprs,
subExprCodes)
+
+ val inputRows = ctx.INPUT_ROW +: getInputRowsForChildren(ctx, expr)
+ val paramsFromRows = inputRows.distinct.filter(_ != null).map { row =>
+ (row, s"InternalRow $row")
+ }
+
+ val paramsLength = getParamLength(ctx, inputAttrs, subExprs) +
paramsFromRows.length
+ // Maximum allowed parameter number for Java's method descriptor.
+ if (paramsLength > 255) {
--- End diff --
is it true for all JVMs?
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