[SYSTEMDS-3764] Fix parser-level constant propagation w/ multi-returns

This patch fixes an old bug of parser-level constant propagation where
updates to scalars through assignments from multi-return function
were not updated the set of constant vars, leading to incorrectly
propagated scalars, constant folding, and utimately wrong results.

This bug was discovered while improving incremental slice line.

scripts/builtin/incSliceLine.dml

@@ -172,8 +172,7 @@ m_incSliceLine = function(
   minsc = -Inf
   if( nrow(prevTK) > 0 ) {
     prevTK2 = oneHotEncodeUsingOffsets(prevTK, foffb, foffe);
-    [minsc2, prevTKC2] = computeLowestPrevTK(prevTK2, X2, totalE, eAvg, alpha)
-    minsc = minsc2; #FIXME otherwise -Inf incorrectly propagated
+    [minsc, prevTKC2] = computeLowestPrevTK(prevTK2, X2, totalE, eAvg, alpha)
   }
 
   # create and score basic slices (conjunctions of 1 feature)

src/main/java/org/apache/sysds/parser/IfStatementBlock.java

@@ -77,20 +77,20 @@ public VariableSet validate(DMLProgram dmlProg, VariableSet ids, HashMap<String,
 
 		/////////////////////////////////////////////////////////////////////////////////
 		//  check data type and value type are same for updated variables in both 
-		//	if statement and else statement
+		//  if statement and else statement
 		//  (reject conditional data type change)
 		/////////////////////////////////////////////////////////////////////////////////
 		for (String updatedVar : this._updated.getVariableNames()){
 			DataIdentifier origVersion  = idsOrigCopy.getVariable(updatedVar);
-			DataIdentifier ifVersion 	= idsIfCopy.getVariable(updatedVar);
+			DataIdentifier ifVersion    = idsIfCopy.getVariable(updatedVar);
 			DataIdentifier elseVersion  = idsElseCopy.getVariable(updatedVar);
 
 			//data type handling: reject conditional data type change
 			if( ifVersion != null && elseVersion != null ) //both branches exist
 			{
 				if (!ifVersion.getOutput().getDataType().equals(elseVersion.getOutput().getDataType())){
 					raiseValidateError("IfStatementBlock has unsupported conditional data type change of variable '"+updatedVar+"' in if/else branch.", conditional);
-				}	
+				}
 			}
 			else if( origVersion !=null ) //only if branch exists
 			{
@@ -99,7 +99,7 @@ else if( origVersion !=null ) //only if branch exists
 				}
 			}
 
-			//value type handling		
+			//value type handling
 			if (ifVersion != null && elseVersion != null && !ifVersion.getOutput().getValueType().equals(elseVersion.getOutput().getValueType())){
 				LOG.warn(elseVersion.printWarningLocation() + "Variable " + elseVersion.getName() + " defined with different value type in if and else clause.");
 			}

src/main/java/org/apache/sysds/parser/StatementBlock.java

@@ -1099,6 +1099,10 @@ else if ( source instanceof BuiltinFunctionExpression || source instanceof Param
 				ids.addVariable(targetList.get(j).getName(), (DataIdentifier)outputs[j]);
 			}
 		}
+
+		// remove updated constant vars (for correctness)
+		for(DataIdentifier target : targetList)
+			currConstVars.remove(target.getName());
 	}
 
 	public void setStatementFormatType(OutputStatement s, boolean conditionalValidate)

src/test/java/org/apache/sysds/test/functions/misc/IPAScalarPropagationMulitReturnTest.java

@@ -0,0 +1,75 @@
+/*
+ * 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.misc;
+
+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;
+
+public class IPAScalarPropagationMulitReturnTest extends AutomatedTestBase 
+{
+	private final static String TEST_NAME1 = "ScalarPropagationMultiReturn";
+	private final static String TEST_DIR = "functions/misc/";
+	private final static String TEST_CLASS_DIR = TEST_DIR + IPAScalarPropagationMulitReturnTest.class.getSimpleName() + "/";
+
+	@Override
+	public void setUp() {
+		TestUtils.clearAssertionInformation();
+		addTestConfiguration( TEST_NAME1, new TestConfiguration(TEST_CLASS_DIR, TEST_NAME1, new String[]{"R"})   );
+	}
+
+	@Test
+	public void testScalarPropagationNoIPA() {
+		runIPAScalarVariablePropagationTest( TEST_NAME1, false );
+	}
+
+	@Test
+	public void testScalarPropagationIPA() {
+		runIPAScalarVariablePropagationTest( TEST_NAME1, true );
+	}
+
+	private void runIPAScalarVariablePropagationTest( String testname, boolean IPA )
+	{
+		boolean oldFlagIPA = OptimizerUtils.ALLOW_INTER_PROCEDURAL_ANALYSIS;
+
+		try {
+			TestConfiguration config = getTestConfiguration(testname);
+			loadTestConfiguration(config);
+
+			String HOME = SCRIPT_DIR + TEST_DIR;
+			fullDMLScriptName = HOME + testname + ".dml";
+			programArgs = new String[]{"-explain","-args", output("R") };
+			OptimizerUtils.ALLOW_INTER_PROCEDURAL_ANALYSIS = IPA;
+
+			//run test, incl expected MR jobs (in case if IPA 0 due to scalar propagation)
+			runTest(true, false, null, IPA ? 0 : 35);
+
+			double[][] ret = TestUtils.convertHashMapToDoubleArray(
+				readDMLMatrixFromOutputDir("R"), 1, 1);
+			Assert.assertEquals(Double.valueOf(2), Double.valueOf(ret[0][0]));
+		}
+		finally {
+			OptimizerUtils.ALLOW_INTER_PROCEDURAL_ANALYSIS = oldFlagIPA;
+		}
+	}
+}

src/test/scripts/functions/misc/ScalarPropagationMultiReturn.dml

@@ -0,0 +1,38 @@
+#-------------------------------------------------------------
+#
+# 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.
+#
+#-------------------------------------------------------------
+
+
+foo = function(matrix[double] A) return (Double minsc, matrix[double] B) {
+  while(FALSE) {} # prevent inlining
+  minsc = min(A);
+  B = A + 7;
+}
+
+X = seq(1,7);
+minsc = -Inf;
+if( avg(X) <= 5 ) {
+  [minsc, X] = foo(X)
+}
+
+# bug: minsc was incorrectly propagated as -Inf, leading to -Inf instead of 2
+R = as.matrix(minsc + 1);
+write(R, $1);
+