Cleanup boolbv quantifier instantiation

1) Do not take references of temporaries.
2) Instead of post_processing, some expressions can be instantiated and
converted immediately.
3) Use skip_typecast rather than local, partial typecast skipping.
4) No need for redundant precondition checks.
5) Mark file-local procedures static.

Author: tautschnig

src/solvers/flattening/boolbv.h

@@ -238,6 +238,11 @@ class boolbvt:public arrayst
   class quantifiert
   {
   public:
+    quantifiert(exprt _expr, literalt _l)
+      : expr(std::move(_expr)), l(std::move(_l))
+    {
+    }
+
     exprt expr;
     literalt l;
   };

src/solvers/flattening/boolbv_quantifier.cpp

@@ -9,28 +9,23 @@ Author: Daniel Kroening, kroening@kroening.com
 #include "boolbv.h"
 
 #include <util/arith_tools.h>
+#include <util/expr_util.h>
 #include <util/invariant.h>
 #include <util/optional.h>
 #include <util/replace_expr.h>
 #include <util/simplify_expr.h>
 
 /// A method to detect equivalence between experts that can contain typecast
-bool expr_eq(const exprt &expr1, const exprt &expr2)
+static bool expr_eq(const exprt &expr1, const exprt &expr2)
 {
-  exprt e1=expr1, e2=expr2;
-  if(expr1.id()==ID_typecast)
-    e1=expr1.op0();
-  if(expr2.id()==ID_typecast)
-    e2=expr2.op0();
-  return e1==e2;
+  return skip_typecast(expr1) == skip_typecast(expr2);
 }
 
 /// To obtain the min value for the quantifier variable of the specified
 /// forall/exists operator. The min variable is in the form of "!(var_expr >
 /// constant)".
-exprt get_quantifier_var_min(
-  const exprt &var_expr,
-  const exprt &quantifier_expr)
+static exprt
+get_quantifier_var_min(const exprt &var_expr, const exprt &quantifier_expr)
 {
   PRECONDITION(quantifier_expr.id() == ID_or || quantifier_expr.id() == ID_and);
 
@@ -75,9 +70,8 @@ exprt get_quantifier_var_min(
 
 /// To obtain the max value for the quantifier variable of the specified
 /// forall/exists operator.
-exprt get_quantifier_var_max(
-  const exprt &var_expr,
-  const exprt &quantifier_expr)
+static exprt
+get_quantifier_var_max(const exprt &var_expr, const exprt &quantifier_expr)
 {
   PRECONDITION(quantifier_expr.id() == ID_or || quantifier_expr.id() == ID_and);
   exprt res = false_exprt();
@@ -132,27 +126,25 @@ exprt get_quantifier_var_max(
   return res;
 }
 
-optionalt<exprt>
+static optionalt<exprt>
 instantiate_quantifier(const quantifier_exprt &expr, const namespacet &ns)
 {
-  PRECONDITION(expr.id() == ID_forall || expr.id() == ID_exists);
-
   const symbol_exprt &var_expr = expr.symbol();
 
   /**
    * We need to rewrite the forall/exists quantifier into
    * an OR/AND expr.
    **/
 
-  const exprt &re = simplify_expr(expr.where(), ns);
+  const exprt re = simplify_expr(expr.where(), ns);
 
   if(re.is_true() || re.is_false())
   {
     return re;
   }
 
-  const exprt &min_i = get_quantifier_var_min(var_expr, re);
-  const exprt &max_i = get_quantifier_var_max(var_expr, re);
+  const exprt min_i = get_quantifier_var_min(var_expr, re);
+  const exprt max_i = get_quantifier_var_max(var_expr, re);
 
   if(min_i.is_false() || max_i.is_false())
     return nullopt;
@@ -183,42 +175,29 @@ instantiate_quantifier(const quantifier_exprt &expr, const namespacet &ns)
   }
 
   UNREACHABLE;
-  return nullopt;
 }
 
 literalt boolbvt::convert_quantifier(const quantifier_exprt &src)
 {
   PRECONDITION(src.id() == ID_forall || src.id() == ID_exists);
 
-  quantifier_exprt expr(src);
-  const auto res = instantiate_quantifier(expr, ns);
-
-  if(!res)
-  {
-    return SUB::convert_rest(src);
-  }
+  const auto res = instantiate_quantifier(src, ns);
 
-  quantifiert quantifier;
-  quantifier.expr = *res;
-  quantifier_list.push_back(quantifier);
+  if(res)
+    return convert_bool(*res);
 
-  literalt l=prop.new_variable();
-  quantifier_list.back().l=l;
+  // we failed to instantiate here, need to pass to post-processing
+  quantifier_list.emplace_back(quantifiert(src, prop.new_variable()));
 
-  return l;
+  return quantifier_list.back().l;
 }
 
 void boolbvt::post_process_quantifiers()
 {
-  std::set<exprt> instances;
-
   if(quantifier_list.empty())
     return;
 
-  for(auto it=quantifier_list.begin();
-      it!=quantifier_list.end();
-      ++it)
-  {
-    prop.set_equal(convert_bool(it->expr), it->l);
-  }
+  // we do not yet have any elaborate post-processing
+  for(const auto &q : quantifier_list)
+    conversion_failed(q.expr);
 }