[SYSTEMDS-3787] New rewrite for transformencode w/o metadata output

This patch add a simple statement block rewrite which checks if the
metadata frame output of transformencode is used at all, and if not
sets a flag on the transformencode operation to avoid allocating and
serializing this meta data. The rewrite applies in about half of all
existing 'org.apache.sysds.test.functions.transform' tests.

src/main/java/org/apache/sysds/hops/rewrite/ProgramRewriter.java

@@ -115,6 +115,7 @@ public ProgramRewriter(boolean staticRewrites, boolean dynamicRewrites)
  				_sbRuleSet.add(  new RewriteMarkLoopVariablesUpdateInPlace()     );
  			if( LineageCacheConfig.getCompAssRW() )
  				_sbRuleSet.add(  new MarkForLineageReuse()                       );
+ 			_sbRuleSet.add(      new RewriteRemoveTransformEncodeMeta()          );
 		}
 
 		// DYNAMIC REWRITES (which do require size information)

src/main/java/org/apache/sysds/hops/rewrite/RewriteRemoveTransformEncodeMeta.java

@@ -0,0 +1,71 @@
+/*
+ * 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.sysds.hops.rewrite;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.sysds.hops.FunctionOp;
+import org.apache.sysds.hops.Hop;
+import org.apache.sysds.hops.LiteralOp;
+import org.apache.sysds.parser.StatementBlock;
+
+/**
+ * Rule: If transformencode procudes a meta data frame which is never
+ * used, flag transformencode to never allocate an serialize this frame.
+ */
+public class RewriteRemoveTransformEncodeMeta extends StatementBlockRewriteRule
+{
+	private final static String TF_OPCODE = "TRANSFORMENCODE";
+
+	@Override
+	public List<StatementBlock> rewriteStatementBlock(StatementBlock sb, ProgramRewriteStatus state)
+	{
+		if( sb.getHops() == null || sb.getHops().isEmpty() )
+			return Arrays.asList(sb);
+
+		//Transformencode is a multi-return FunctionOp and always appears as root
+		//of the DAG. We then check that the meta data object is never used,
+		//that is, the meta data is not in the live-out variables of the statementblock
+		Hop root = sb.getHops().get(0);
+		if( root instanceof FunctionOp
+			&& TF_OPCODE.equals(((FunctionOp)root).getFunctionName()) )
+		{
+			FunctionOp func = (FunctionOp)root;
+			if( !sb.liveOut().containsVariable(func.getOutputVariableNames()[1])
+				&& func.getInput().size() == 2) { //not added yet
+				func.getInput().add(new LiteralOp(false));
+				LOG.debug("Applied removeTransformEncodeMeta (line "+ func.getBeginLine() +").");
+			}
+		}
+
+		return Arrays.asList(sb);
+	}
+
+	@Override
+	public List<StatementBlock> rewriteStatementBlocks(List<StatementBlock> sbs, ProgramRewriteStatus sate) {
+		return sbs;
+	}
+
+	@Override
+	public boolean createsSplitDag() {
+		return false;
+	}
+}

src/main/java/org/apache/sysds/runtime/instructions/cp/MultiReturnParameterizedBuiltinCPInstruction.java

@@ -39,11 +39,13 @@
 
 public class MultiReturnParameterizedBuiltinCPInstruction extends ComputationCPInstruction {
 	protected final ArrayList<CPOperand> _outputs;
-
+	protected final boolean _metaReturn;
+
 	private MultiReturnParameterizedBuiltinCPInstruction(Operator op, CPOperand input1, CPOperand input2,
-		ArrayList<CPOperand> outputs, String opcode, String istr) {
+		boolean metaReturn, ArrayList<CPOperand> outputs, String opcode, String istr) {
 		super(CPType.MultiReturnBuiltin, op, input1, input2, outputs.get(0), opcode, istr);
 		_outputs = outputs;
+		_metaReturn = metaReturn;
 	}
 
 	public CPOperand getOutput(int i) {
@@ -67,9 +69,14 @@ public static MultiReturnParameterizedBuiltinCPInstruction parseInstruction(Stri
 			// one input and two outputs
 			CPOperand in1 = new CPOperand(parts[1]);
 			CPOperand in2 = new CPOperand(parts[2]);
-			outputs.add(new CPOperand(parts[3], ValueType.FP64, DataType.MATRIX));
-			outputs.add(new CPOperand(parts[4], ValueType.STRING, DataType.FRAME));
-			return new MultiReturnParameterizedBuiltinCPInstruction(null, in1, in2, outputs, opcode, str);
+			int pos = 3;
+			boolean metaReturn = true;
+			if( parts.length == 7 ) //no need for meta data
+				metaReturn = new CPOperand(parts[pos++]).getLiteral().getBooleanValue();
+			outputs.add(new CPOperand(parts[pos], ValueType.FP64, DataType.MATRIX));
+			outputs.add(new CPOperand(parts[pos+1], ValueType.STRING, DataType.FRAME));
+			return new MultiReturnParameterizedBuiltinCPInstruction(
+				null, in1, in2, metaReturn, outputs, opcode, str);
 		}
 		else {
 			throw new DMLRuntimeException("Invalid opcode in MultiReturnBuiltin instruction: " + opcode);
@@ -87,9 +94,10 @@ public void processInstruction(ExecutionContext ec) {
 		// execute block transform encode
 		MultiColumnEncoder encoder = EncoderFactory.createEncoder(spec, colnames, fin.getNumColumns(), null);
 		// TODO: Assign #threads in compiler and pass via the instruction string
+		int k = OptimizerUtils.getTransformNumThreads();
 		MatrixBlock data = encoder.encode(fin, OptimizerUtils.getTransformNumThreads()); // build and apply
-		FrameBlock meta = encoder.getMetaData(new FrameBlock(fin.getNumColumns(), ValueType.STRING), 
-				OptimizerUtils.getTransformNumThreads());
+		FrameBlock meta = !_metaReturn ? new FrameBlock() :
+			encoder.getMetaData(new FrameBlock(fin.getNumColumns(), ValueType.STRING), k);
 		meta.setColumnNames(colnames);
 
 		// release input and outputs

src/main/java/org/apache/sysds/runtime/instructions/spark/MultiReturnParameterizedBuiltinSPInstruction.java

@@ -77,10 +77,12 @@
 
 public class MultiReturnParameterizedBuiltinSPInstruction extends ComputationSPInstruction {
 	protected ArrayList<CPOperand> _outputs;
+	protected final boolean _metaReturn;
 
 	private MultiReturnParameterizedBuiltinSPInstruction(Operator op, CPOperand input1, CPOperand input2,
-		ArrayList<CPOperand> outputs, String opcode, String istr) {
+		boolean metaReturn, ArrayList<CPOperand> outputs, String opcode, String istr) {
 		super(SPType.MultiReturnBuiltin, op, input1, input2, outputs.get(0), opcode, istr);
+		_metaReturn = metaReturn;
 		_outputs = outputs;
 	}
 
@@ -93,14 +95,17 @@ public static MultiReturnParameterizedBuiltinSPInstruction parseInstruction(Stri
 			// one input and two outputs
 			CPOperand in1 = new CPOperand(parts[1]);
 			CPOperand in2 = new CPOperand(parts[2]);
-			outputs.add(new CPOperand(parts[3], ValueType.FP64, DataType.MATRIX));
-			outputs.add(new CPOperand(parts[4], ValueType.STRING, DataType.FRAME));
-			return new MultiReturnParameterizedBuiltinSPInstruction(null, in1, in2, outputs, opcode, str);
+			int pos = 3;
+			boolean metaReturn = true;
+			if( parts.length == 6 ) //no need for meta data
+				metaReturn = new CPOperand(parts[pos++]).getLiteral().getBooleanValue();
+			outputs.add(new CPOperand(parts[pos], ValueType.FP64, DataType.MATRIX));
+			outputs.add(new CPOperand(parts[pos+1], ValueType.STRING, DataType.FRAME));
+			return new MultiReturnParameterizedBuiltinSPInstruction(null, in1, in2, metaReturn, outputs, opcode, str);
 		}
 		else {
 			throw new DMLRuntimeException("Invalid opcode in MultiReturnBuiltin instruction: " + opcode);
 		}
-
 	}
 
 	@Override
@@ -112,8 +117,8 @@ public void processInstruction(ExecutionContext ec) {
 			// get input RDD and meta data
 			FrameObject fo = sec.getFrameObject(input1.getName());
 			FrameObject fometa = sec.getFrameObject(_outputs.get(1).getName());
-			JavaPairRDD<Long, FrameBlock> in = (JavaPairRDD<Long, FrameBlock>) sec.getRDDHandleForFrameObject(fo,
-				FileFormat.BINARY);
+			JavaPairRDD<Long, FrameBlock> in = (JavaPairRDD<Long, FrameBlock>) 
+				sec.getRDDHandleForFrameObject(fo, FileFormat.BINARY);
 			String spec = ec.getScalarInput(input2).getStringValue();
 			DataCharacteristics mcIn = sec.getDataCharacteristics(input1.getName());
 			DataCharacteristics mcOut = sec.getDataCharacteristics(output.getName());
@@ -163,7 +168,10 @@ public void processInstruction(ExecutionContext ec) {
 			// set output and maintain lineage/output characteristics
 			sec.setRDDHandleForVariable(_outputs.get(0).getName(), out);
 			sec.addLineageRDD(_outputs.get(0).getName(), input1.getName());
-			sec.setFrameOutput(_outputs.get(1).getName(), meta);
+			if( _metaReturn )
+				sec.setFrameOutput(_outputs.get(1).getName(), meta);
+			else
+				sec.setFrameOutput(_outputs.get(1).getName(), new FrameBlock());
 		}
 		catch(IOException ex) {
 			throw new RuntimeException(ex);