improved inStream

define `0/0` for inStream-equation as first `stream_exp`

refs ticket:4869

Belonging to [master]:
  - #2346
  - OpenModelica/OpenModelica-testsuite#917

Author: vruge

Compiler/BackEnd/BackendDAEOptimize.mo

@@ -152,7 +152,7 @@ algorithm
     local
       DAE.Type tp;
       DAE.ComponentRef cr;
-      DAE.Exp e, expr;
+      DAE.Exp e, expr, a, b;
       Option<DAE.Exp> eMin, eMax;
       Boolean isZero;
 
@@ -177,6 +177,20 @@ algorithm
       //print(ExpressionDump.printExpStr(e));
     then Expression.makePureBuiltinCall("max", {e, expr}, Expression.typeof(e));
 
+    case DAE.CALL(path=Absyn.IDENT("$OMC$inStreamDiv"),expLst={e, expr})
+      algorithm
+          e := ExpressionSimplify.simplify(e);
+          expr := match(e)
+                      case DAE.BINARY(a, DAE.DIV(), b)
+                        guard Expression.isZero(a) and Expression.isZero(b)
+                      then
+                        expr;
+                      else
+                        e;
+                 end match;
+      then
+         expr;
+
     else inExp;
   end match;
 end simplifyInStreamWork2;

Compiler/FrontEnd/ConnectUtil.mo

@@ -2487,7 +2487,7 @@ algorithm
     local
       DAE.ComponentRef c;
       Face f1, f2;
-      DAE.Exp e;
+      DAE.Exp e, expr;
       list<ConnectorElement>  inside, outside;
 
     // Unconnected stream connector:
@@ -2524,6 +2524,10 @@ algorithm
         (outside, inside) := List.splitOnTrue(reducedStreams, isOutsideElement);
         inside := removeStreamSetElement(streamCref, inside);
         e := streamSumEquationExp(outside, inside, flowThreshold);
+        if not listEmpty(inside) then
+          expr := streamFlowExp(List.first(inside));
+          e := Expression.makePureBuiltinCall("$OMC$inStreamDiv", {e, expr}, Expression.typeof(e));
+        end if;
         // Evaluate any inStream calls that were generated.
         e := evaluateConnectionOperators2(e, sets, setArray, false, flowThreshold);
       then