Corrected simplify lhs in ai_domain_baset

The boolean flag was the wrong way round for ai_simplify_lhs - this
corrects this.

Author: thk123

src/analyses/ai.cpp

@@ -57,29 +57,33 @@ bool ai_domain_baset::ai_simplify_lhs(
   if(condition.id()==ID_index)
   {
     index_exprt ie=to_index_expr(condition);
-    bool changed=ai_simplify(ie.index(), ns);
-    if(changed)
+    bool no_simplification=ai_simplify(ie.index(), ns);
+    if(!no_simplification)
       condition=simplify_expr(ie, ns);
 
-    return !changed;
+    return no_simplification;
   }
   else if(condition.id()==ID_dereference)
   {
     dereference_exprt de=to_dereference_expr(condition);
-    bool changed=ai_simplify(de.pointer(), ns);
-    if(changed)
+    bool no_simplification=ai_simplify(de.pointer(), ns);
+    if(!no_simplification)
       condition=simplify_expr(de, ns);  // So *(&x) -> x
 
-    return !changed;
+    return no_simplification;
   }
   else if(condition.id()==ID_member)
   {
     member_exprt me=to_member_expr(condition);
-    bool changed=ai_simplify_lhs(me.compound(), ns); // <-- lhs!
-    if(changed)
+    // Since simplify_ai_lhs is required to return an addressable object
+    // (so remains a valid left hand side), to simplify
+    // `(something_simplifiable).b` we require that `something_simplifiable`
+    // must also be addressable
+    bool no_simplification=ai_simplify_lhs(me.compound(), ns);
+    if(!no_simplification)
       condition=simplify_expr(me, ns);
 
-    return !changed;
+    return no_simplification;
   }
   else
     return true;