reduce inStream equations for zero flow (#3430)

Compiler/FrontEnd/ConnectUtil.mo

@@ -2822,28 +2822,53 @@ protected function streamSumEquationExp
   output DAE.Exp outSumExp;
 protected
   DAE.Exp outside_sum1, outside_sum2, inside_sum1, inside_sum2, res;
+  list<ConnectorElement> insideElements, outsideElements;
 algorithm
-  if listEmpty(inOutsideElements) then
+  (_, insideElements) := List.splitOnTrue(inInsideElements, function isZeroFlow(attr="min"));
+  (_, outsideElements) := List.splitOnTrue(inOutsideElements, function isZeroFlow(attr="max"));
+  if listEmpty(outsideElements) then
     // No outside components.
-    inside_sum1 := sumMap(inInsideElements, sumInside1, inFlowThreshold);
-    inside_sum2 := sumMap(inInsideElements, sumInside2, inFlowThreshold);
+    inside_sum1 := sumMap(insideElements, sumInside1, inFlowThreshold);
+    inside_sum2 := sumMap(insideElements, sumInside2, inFlowThreshold);
     outSumExp := Expression.expDiv(inside_sum1, inside_sum2);
-  elseif listEmpty(inInsideElements) then
+  elseif listEmpty(insideElements) then
     // No inside components.
-    outside_sum1 := sumMap(inOutsideElements, sumOutside1, inFlowThreshold);
-    outside_sum2 := sumMap(inOutsideElements, sumOutside2, inFlowThreshold);
+    outside_sum1 := sumMap(outsideElements, sumOutside1, inFlowThreshold);
+    outside_sum2 := sumMap(outsideElements, sumOutside2, inFlowThreshold);
     outSumExp := Expression.expDiv(outside_sum1, outside_sum2);
   else
     // Both outside and inside components.
-    outside_sum1 := sumMap(inOutsideElements, sumOutside1, inFlowThreshold);
-    outside_sum2 := sumMap(inOutsideElements, sumOutside2, inFlowThreshold);
-    inside_sum1 := sumMap(inInsideElements, sumInside1, inFlowThreshold);
-    inside_sum2 := sumMap(inInsideElements, sumInside2, inFlowThreshold);
+    outside_sum1 := sumMap(outsideElements, sumOutside1, inFlowThreshold);
+    outside_sum2 := sumMap(outsideElements, sumOutside2, inFlowThreshold);
+    inside_sum1 := sumMap(insideElements, sumInside1, inFlowThreshold);
+    inside_sum2 := sumMap(insideElements, sumInside2, inFlowThreshold);
     outSumExp := Expression.expDiv(Expression.expAdd(outside_sum1, inside_sum1),
                                    Expression.expAdd(outside_sum2, inside_sum2));
   end if;
 end streamSumEquationExp;
 
+protected function isZeroFlow
+  "Returns true if the given flow attribute of a connector is zero."
+  input ConnectorElement inElement;
+  input String attr;
+  output Boolean isZero;
+protected
+  DAE.Type ty;
+  Option<DAE.Exp> attr_oexp;
+  DAE.Exp flow_exp, attr_exp;
+algorithm
+  flow_exp := flowExp(inElement);
+  ty := Expression.typeof(flow_exp);
+  attr_oexp := Types.lookupAttributeExp(Types.getAttributes(ty), attr);
+  isZero := false;
+  if isSome(attr_oexp) then
+    SOME(attr_exp) := attr_oexp;
+    isZero := Expression.isZero(attr_exp);
+  else
+    isZero := false;
+  end if;
+end isZeroFlow;
+
 protected function sumMap
   "Creates a sum expression by applying the given function on the list of
   elements and summing up the resulting expressions."