[SYSTEMDS-3804] New rewrite for reverse sequences

This patch adds a new rewrite rev(seq(1,n)) -> seq(n,1), a pattern
we recently saw in a script on vectorized time series forecasting.

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

@@ -153,8 +153,9 @@ private void rule_AlgebraicSimplification(Hop hop, boolean descendFirst)
 			hi = canonicalizeMatrixMultScalarAdd(hi);            //e.g., eps+U%*%t(V) -> U%*%t(V)+eps, U%*%t(V)-eps -> U%*%t(V)+(-eps) 
 			hi = simplifyCTableWithConstMatrixInputs(hi);        //e.g., table(X, matrix(1,...)) -> table(X, 1)
 			hi = removeUnnecessaryCTable(hop, hi, i);            //e.g., sum(table(X, 1)) -> nrow(X) and sum(table(1, Y)) -> nrow(Y) and sum(table(X, Y)) -> nrow(X)
-			hi = simplifyConstantConjunction(hop, hi, i);       //e.g., a & !a -> FALSE 
+			hi = simplifyConstantConjunction(hop, hi, i);        //e.g., a & !a -> FALSE 
 			hi = simplifyReverseOperation(hop, hi, i);           //e.g., table(seq(1,nrow(X),1),seq(nrow(X),1,-1)) %*% X -> rev(X)
+			hi = simplifyReverseSequence(hop, hi, i);            //e.g., rev(seq(1,n)) -> seq(n,1)
 			if(OptimizerUtils.ALLOW_OPERATOR_FUSION)
 				hi = simplifyMultiBinaryToBinaryOperation(hi);       //e.g., 1-X*Y -> X 1-* Y
 			hi = simplifyDistributiveBinaryOperation(hop, hi, i);//e.g., (X-Y*X) -> (1-Y)*X
@@ -798,6 +799,28 @@ private static Hop simplifyReverseOperation( Hop parent, Hop hi, int pos )
 
 		return hi;
 	}
+
+	private static Hop simplifyReverseSequence( Hop parent, Hop hi, int pos )
+	{
+		if( HopRewriteUtils.isReorg(hi, ReOrgOp.REV) 
+			&& HopRewriteUtils.isBasic1NSequence(hi.getInput(0))
+			&& hi.getInput(0).getParent().size() == 1) //only consumer
+		{
+			DataGenOp seq = (DataGenOp) hi.getInput(0);
+			Hop from = seq.getInput().get(seq.getParamIndex(Statement.SEQ_FROM));
+			Hop to = seq.getInput().get(seq.getParamIndex(Statement.SEQ_TO));
+			seq.getInput().set(seq.getParamIndex(Statement.SEQ_FROM), to);
+			seq.getInput().set(seq.getParamIndex(Statement.SEQ_TO), from);
+			seq.getInput().set(seq.getParamIndex(Statement.SEQ_INCR), new LiteralOp(-1));
+
+			HopRewriteUtils.replaceChildReference(parent, hi, seq, pos);
+			HopRewriteUtils.cleanupUnreferenced(hi, seq);
+			hi = seq;
+			LOG.debug("Applied simplifyReverseSequence (line "+hi.getBeginLine()+").");
+		}
+
+		return hi;
+	}
 
 	private static Hop simplifyMultiBinaryToBinaryOperation( Hop hi )
 	{

src/test/java/org/apache/sysds/test/functions/rewrite/RewriteRemoveUnnecessaryRevTest.java

@@ -0,0 +1,81 @@
+/*
+ * 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.test.functions.rewrite;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import org.apache.sysds.hops.OptimizerUtils;
+import org.apache.sysds.test.AutomatedTestBase;
+import org.apache.sysds.test.TestConfiguration;
+import org.apache.sysds.test.TestUtils;
+import org.apache.sysds.runtime.matrix.data.MatrixValue.CellIndex;
+
+public class RewriteRemoveUnnecessaryRevTest extends AutomatedTestBase 
+{
+	private static final String TEST_NAME1 = "RewriteRemoveUnnecessaryRev";
+
+	private static final String TEST_DIR = "functions/rewrite/";
+	private static final String TEST_CLASS_DIR = TEST_DIR + RewritePushdownSumBinaryMult.class.getSimpleName() + "/";
+
+	@Override
+	public void setUp() {
+		TestUtils.clearAssertionInformation();
+		addTestConfiguration( TEST_NAME1, new TestConfiguration(TEST_CLASS_DIR, TEST_NAME1, new String[] { "R" }) );
+	}
+
+	@Test
+	public void testRemoveSeqRevRewrite() {
+		testRewriteRemoveSeqRev( TEST_NAME1, true );
+	}
+
+	@Test
+	public void testRemoveSeqRevNoRewrite() {
+		testRewriteRemoveSeqRev( TEST_NAME1, false );
+	}
+
+	private void testRewriteRemoveSeqRev( String testname, boolean rewrites )
+	{
+		boolean oldFlag = OptimizerUtils.ALLOW_ALGEBRAIC_SIMPLIFICATION;
+		int rows = 1001;
+
+		try
+		{
+			TestConfiguration config = getTestConfiguration(testname);
+			loadTestConfiguration(config);
+
+			String HOME = SCRIPT_DIR + TEST_DIR;
+			fullDMLScriptName = HOME + testname + ".dml";
+			programArgs = new String[]{ "-stats","-args", String.valueOf(rows), output("Scalar") };
+			OptimizerUtils.ALLOW_ALGEBRAIC_SIMPLIFICATION = rewrites;
+
+			runTest(true, false, null, -1); 
+
+			//compare scalars 
+			int ret = (int)readDMLScalarFromOutputDir("Scalar").get(new CellIndex(1,1)).doubleValue();
+			Assert.assertEquals(ret, rows*(rows+1)/2);
+			if( rewrites )
+				Assert.assertFalse(heavyHittersContainsString("rev"));
+		}
+		finally {
+			OptimizerUtils.ALLOW_ALGEBRAIC_SIMPLIFICATION = oldFlag;
+		}
+	}
+}

src/test/scripts/functions/rewrite/RewriteRemoveUnnecessaryRev.dml

@@ -0,0 +1,31 @@
+#-------------------------------------------------------------
+#
+# 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.
+#
+#-------------------------------------------------------------
+
+rows = $1;
+
+# to be rewritten to: seq(rows,1)
+X = rev(seq(1,rows))
+
+while(FALSE){}
+
+R = sum(X);
+write(R, $2)
+