Fix flattening of if-equations (#12373)

- Flatten the condition of an if-equation branch after evaluating it.

Fixes #12368

OMCompiler/Compiler/NFFrontEnd/NFFlatten.mo

@@ -1820,6 +1820,7 @@ algorithm
               // happen if scalarization is turned off and for-loops aren't unrolled.
               if settings.scalarize or not Expression.contains(cond, Expression.isIterator) then
                 cond := Ceval.evalExp(cond, target);
+                cond := flattenExp(cond, prefix);
               end if;
             end if;
 
@@ -1861,6 +1862,7 @@ algorithm
         algorithm
           if var <= Variability.STRUCTURAL_PARAMETER then
             cond := Ceval.evalExp(cond, target);
+            cond := flattenExp(cond, prefix);
           end if;
 
           if not Expression.isFalse(cond) then

testsuite/flattening/modelica/scodeinst/IfEquation9.mo

@@ -0,0 +1,45 @@
+// name: IfEquation9
+// keywords:
+// status: correct
+// cflags: -d=newInst
+//
+
+model A
+  Real x;
+  parameter Boolean b;
+equation
+  if b then
+    x = 2;
+  else
+    x = 3;
+  end if;
+end A;
+
+model IfEquation9
+  parameter Boolean barr[6] = {false, false, true, false, true, false};
+  A a[4](b = barr[1:4]);
+end IfEquation9;
+
+// Result:
+// class IfEquation9
+//   parameter Boolean barr[1] = false;
+//   parameter Boolean barr[2] = false;
+//   parameter Boolean barr[3] = true;
+//   parameter Boolean barr[4] = false;
+//   parameter Boolean barr[5] = true;
+//   parameter Boolean barr[6] = false;
+//   Real a[1].x;
+//   final parameter Boolean a[1].b = false;
+//   Real a[2].x;
+//   final parameter Boolean a[2].b = false;
+//   Real a[3].x;
+//   final parameter Boolean a[3].b = true;
+//   Real a[4].x;
+//   final parameter Boolean a[4].b = false;
+// equation
+//   a[1].x = 3.0;
+//   a[2].x = 3.0;
+//   a[3].x = 2.0;
+//   a[4].x = 3.0;
+// end IfEquation9;
+// endResult

testsuite/flattening/modelica/scodeinst/Makefile

@@ -727,6 +727,7 @@ IfEquation5.mo \
 IfEquation6.mo \
 IfEquation7.mo \
 IfEquation8.mo \
+IfEquation9.mo \
 IfEquationEval1.mo \
 IfEquationEval2.mo \
 IfEquationEval3.mo \