[SYSTEMDS-3806] Robustness simplifyDotProductSum rewrite

This patch fixes an issue of incorrect application of the
simplifyDotProductSum rewrite. Specifically, sum(s*V) was rewritten to
t(s) %*% V because s was assumed to be a vector of equal size than V
but was a scalar. The root cause of an incorrect size propagation for
the new scalar right indexing, but for robustness we now also check
that both inputs are actually matrices.

src/main/java/org/apache/sysds/hops/IndexingOp.java

@@ -370,6 +370,14 @@ private static IndexingMethod optFindIndexingMethod( boolean singleRow, boolean
 	@Override
 	public void refreshSizeInformation()
 	{
+		// early abort for scalar right indexing
+		// (important to prevent incorrect dynamic rewrites)
+		if( isScalar() ) {
+			setDim1(0); 
+			setDim2(0);
+			return;
+		}
+
 		Hop input1 = getInput().get(0); //matrix
 		Hop input2 = getInput().get(1); //inpRowL
 		Hop input3 = getInput().get(2); //inpRowU

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

@@ -2312,6 +2312,7 @@ private static Hop simplifyDotProductSum(Hop parent, Hop hi, int pos) {
 			//check for sum(v1*v2), but prevent to rewrite sum(v1*v2*v3) which is later compiled into a ta+* lop
 			else if( HopRewriteUtils.isBinary(hi2, OpOp2.MULT, 1) //no other consumer than sum
 					&& hi2.getInput().get(0).getDim2()==1 && hi2.getInput().get(1).getDim2()==1
+					&& hi2.getInput().get(0).isMatrix() && hi2.getInput().get(1).isMatrix()
 					&& !HopRewriteUtils.isBinary(hi2.getInput().get(0), OpOp2.MULT)
 					&& !HopRewriteUtils.isBinary(hi2.getInput().get(1), OpOp2.MULT)
 					&& ( !ALLOW_SUM_PRODUCT_REWRITES

src/test/scripts/functions/unary/matrix/eigen.dml

@@ -33,9 +33,7 @@ numEval = $2;
 D = matrix(1, numEval, 1);
 for ( i in 1:numEval ) {
     Av = A %*% evec[,i];
-    while(FALSE){} #fix incorrect rewrite sequence
     rhs = as.scalar(eval[i,1]) * evec[,i];
-    while(FALSE){} #fix incorrect rewrite sequence
     diff = sum(Av-rhs);
     D[i,1] = diff;
 }