/*
* Licensed 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 com.facebook.presto.sql.gen;
import com.facebook.presto.byteCode.Block;
import com.facebook.presto.byteCode.ByteCodeNode;
import com.facebook.presto.byteCode.CompilerContext;
import com.facebook.presto.byteCode.control.IfStatement;
import com.facebook.presto.metadata.Signature;
import com.facebook.presto.spi.type.Type;
import com.facebook.presto.sql.relational.RowExpression;
import com.google.common.collect.Lists;
import java.util.ArrayList;
import java.util.List;
import static com.facebook.presto.byteCode.OpCodes.NOP;
public class CoalesceCodeGenerator
implements ByteCodeGenerator
{
@Override
public ByteCodeNode generateExpression(Signature signature, ByteCodeGeneratorContext generatorContext, Type returnType, List<RowExpression> arguments)
{
List<ByteCodeNode> operands = new ArrayList<>();
for (RowExpression expression : arguments) {
operands.add(generatorContext.generate(expression));
}
CompilerContext context = generatorContext.getContext();
ByteCodeNode nullValue = new Block(context)
.putVariable("wasNull", true)
.pushJavaDefault(returnType.getJavaType());
// reverse list because current if statement builder doesn't support if/else so we need to build the if statements bottom up
for (ByteCodeNode operand : Lists.reverse(operands)) {
Block condition = new Block(context)
.append(operand)
.getVariable("wasNull");
// if value was null, pop the null value, clear the null flag, and process the next operand
Block nullBlock = new Block(context)
.pop(returnType.getJavaType())
.putVariable("wasNull", false)
.append(nullValue);
nullValue = new IfStatement(context, condition, nullBlock, NOP);
}
return nullValue;
}
}