[BE] Improve inlining and solution of array equations

Belonging to [master]:
  - #2793
  - OpenModelica/OpenModelica-testsuite#1079

Compiler/BackEnd/BackendInline.mo

@@ -210,8 +210,13 @@ algorithm
         (e1_1,source,b1,_) = Inline.inlineExp(e1,fns,source);
         (e2_1,source,b2,_) = Inline.inlineExp(e2,fns,source);
         true = b1 or b2;
+        eqn = match (e1_1, e2_1)
+          case (DAE.ARRAY(array = {e1}), DAE.ARRAY(array = {e2}))
+          then BackendDAE.EQUATION(e1,e2,source,attr); // flatten if size==1
+          else BackendDAE.ARRAY_EQUATION(dimSize,e1_1,e2_1,source,attr);
+        end match;
       then
-        (BackendDAE.ARRAY_EQUATION(dimSize,e1_1,e2_1,source,attr),true);
+        (eqn, true);
 
     case(BackendDAE.FOR_EQUATION(e, e1, e2, eqn, source, attr), _)
       equation

Compiler/BackEnd/Differentiate.mo

@@ -1056,6 +1056,7 @@ algorithm
     // case for arrays
     case ((e as DAE.CREF(ty = DAE.T_ARRAY())), _, _, diffType, _) guard ( match diffType case BackendDAE.GENERIC_GRADIENT() then false; else true; end match )
       equation
+        true = Flags.isSet(Flags.NF_SCALARIZE); // only expand if scalarize
         (e1,true) = Expression.extendArrExp(e,false);
         (res, outFunctionTree) = differentiateExp(e1, inDiffwrtCref, inInputData, inDiffType, inFunctionTree, maxIter);
       then
@@ -1070,7 +1071,7 @@ algorithm
     case (DAE.CREF(componentRef = cr, ty = tp), _, _, _, _)
       equation
         true = ComponentReference.crefEqual(cr, inDiffwrtCref);
-        one = Expression.makeConstOne(tp);
+        (one,_) = Expression.makeOneExpression(Expression.arrayDimension(tp));
       then
         (one, inFunctionTree);
 

Compiler/FrontEnd/ExpressionSimplify.mo

@@ -2397,6 +2397,13 @@ algorithm
       then
         exp;
 
+    // Scalar product of any expression with zeros
+    case (_, _)
+      equation
+        true = Expression.isZero(inVector1) or Expression.isZero(inVector2);
+      then
+        Expression.makeConstZero(DAE.T_REAL_DEFAULT);
+
   end match;
 end simplifyScalarProduct;