kangkaisen commented on a change in pull request #255: Simplify constant Expr URL: https://github.com/apache/incubator-doris/pull/255#discussion_r230672079
########## File path: fe/src/main/java/org/apache/doris/rewrite/FoldConstantsRule.java ########## @@ -0,0 +1,233 @@ +// 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.doris.rewrite; + + +import com.google.common.collect.ArrayListMultimap; +import com.google.common.collect.Multimap; +import org.apache.doris.analysis.Analyzer; +import org.apache.doris.analysis.ArithmeticExpr; +import org.apache.doris.analysis.CastExpr; +import org.apache.doris.analysis.Expr; +import org.apache.doris.analysis.FunctionCallExpr; +import org.apache.doris.analysis.LiteralExpr; +import org.apache.doris.analysis.NullLiteral; +import org.apache.doris.catalog.Function; +import org.apache.doris.catalog.ScalarType; +import org.apache.doris.catalog.Type; +import org.apache.doris.common.AnalysisException; + +import java.lang.reflect.InvocationTargetException; +import java.lang.reflect.Method; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.List; +import java.util.Objects; + +/** + * This rule replaces a constant Expr with its equivalent LiteralExpr by evaluating the + * Expr in the BE. Exprs that are already LiteralExprs are not changed. + * + * TODO: Expressions fed into this rule are currently not required to be analyzed + * in order to support constant folding in expressions that contain unresolved + * references to select-list aliases (such expressions cannot be analyzed). + * The cross-dependencies between rule transformations and analysis are vague at the + * moment and make rule application overly complicated. + * + * Examples: + * 1 + 1 + 1 --> 3 + * toupper('abc') --> 'ABC' + * cast('2016-11-09' as timestamp) --> TIMESTAMP '2016-11-09 00:00:00' + */ +public class FoldConstantsRule implements ExprRewriteRule { + public static ExprRewriteRule INSTANCE = new FoldConstantsRule(); + + private Multimap<String, FEFunctionInvoker> functions = ArrayListMultimap.create(); + + @Override + public Expr apply(Expr expr, Analyzer analyzer) throws AnalysisException { + if (functions.isEmpty()) { + registerFunctions(); + } + + // Avoid calling Expr.isConstant() because that would lead to repeated traversals + // of the Expr tree. Assumes the bottom-up application of this rule. Constant + // children should have been folded at this point. + for (Expr child : expr.getChildren()) { + if (!child.isLiteral() && !(child instanceof CastExpr)) { + return expr; + } + } + + if (expr.isLiteral() || !expr.isConstant()) { + return expr; + } + + // Do not constant fold cast(null as dataType) because we cannot preserve the + // cast-to-types and that can lead to query failures, e.g., CTAS + if (expr instanceof CastExpr) { + CastExpr castExpr = (CastExpr) expr; + if (castExpr.getChild(0) instanceof NullLiteral) { + return expr; + } + } + // Analyze constant exprs, if necessary. Note that the 'expr' may become non-constant + // after analysis (e.g., aggregate functions). + if (!expr.isAnalyzed()) { + expr.analyze(analyzer); + if (!expr.isConstant()) { + return expr; + } + } + return simplify(expr); + } + + private Expr simplify(Expr constExpr) throws AnalysisException { + if (constExpr instanceof ArithmeticExpr + || constExpr instanceof FunctionCallExpr + || constExpr instanceof CastExpr) { + Function fn = constExpr.getFn(); + List<ScalarType> argTypes = new ArrayList<>(); + for (Type type : fn.getArgs()) { + argTypes.add((ScalarType) type); + } + FEFunctionSignature signature = new FEFunctionSignature(fn.functionName(), + argTypes.toArray(new ScalarType[argTypes.size()]), (ScalarType) fn.getReturnType()); + FEFunctionInvoker invoker = getFunction(signature); + if (invoker != null) { + try { + return invoker.invoke(constExpr.getChildrenWithoutCast()); + } catch (AnalysisException e) { + return constExpr; + } + } + } + return constExpr; + } + + private FEFunctionInvoker getFunction(FEFunctionSignature signature) { + Collection<FEFunctionInvoker> functionInvokers = functions.get(signature.getName()); + + if (functionInvokers == null) { + return null; + } + + for (FEFunctionInvoker invoker : functionInvokers) { + if (!invoker.getSignature().returnType.equals(signature.getReturnType())) { + continue; + } + + ScalarType[] argTypes1 = invoker.getSignature().getArgTypes(); + ScalarType[] argTypes2 = signature.getArgTypes(); + + if (!Arrays.equals(argTypes1, argTypes2)) { + continue; + } + + return invoker; + } + return null; + } + + private void registerFunctions() { Review comment: Yes. 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