simplifier: new interface for simplify_if

This improves type safety.

Author: Daniel Kroening

src/util/simplify_expr.cpp

@@ -991,9 +991,7 @@ simplify_exprt::simplify_dereference(const dereference_exprt &expr)
 
     if_exprt tmp{if_expr.cond(), tmp_op1_result, tmp_op2_result};
 
-    simplify_if(tmp);
-
-    return tmp;
+    return changed(simplify_if(tmp));
   }
 
   if(pointer.id()==ID_address_of)
@@ -1311,13 +1309,12 @@ bool simplify_exprt::simplify_if_preorder(if_exprt &expr)
   return result;
 }
 
-bool simplify_exprt::simplify_if(if_exprt &expr)
+NODISCARD simplify_exprt::resultt<>
+simplify_exprt::simplify_if(const if_exprt &expr)
 {
-  exprt &cond=expr.cond();
-  exprt &truevalue=expr.true_case();
-  exprt &falsevalue=expr.false_case();
-
-  bool result=true;
+  const exprt &cond = expr.cond();
+  const exprt &truevalue = expr.true_case();
+  const exprt &falsevalue = expr.false_case();
 
   if(do_simplify_if)
   {
@@ -1333,26 +1330,21 @@ bool simplify_exprt::simplify_if(if_exprt &expr)
       if(truevalue.is_true() && falsevalue.is_false())
       {
         // a?1:0 <-> a
-        exprt tmp;
-        tmp.swap(cond);
-        expr.swap(tmp);
-        return false;
+        return cond;
       }
       else if(truevalue.is_false() && falsevalue.is_true())
       {
         // a?0:1 <-> !a
         exprt tmp = boolean_negate(cond);
         simplify_node(tmp);
-        expr.swap(tmp);
-        return false;
+        return std::move(tmp);
       }
       else if(falsevalue.is_false())
       {
         // a?b:0 <-> a AND b
         and_exprt tmp(cond, truevalue);
         simplify_node(tmp);
-        expr.swap(tmp);
-        return false;
+        return std::move(tmp);
       }
       else if(falsevalue.is_true())
       {
@@ -1361,16 +1353,14 @@ bool simplify_exprt::simplify_if(if_exprt &expr)
         simplify_node(tmp_not_cond);
         or_exprt tmp(tmp_not_cond, truevalue);
         simplify_node(tmp);
-        expr.swap(tmp);
-        return false;
+        return std::move(tmp);
       }
       else if(truevalue.is_true())
       {
         // a?1:b <-> a||(!a && b) <-> a OR b
         or_exprt tmp(cond, falsevalue);
         simplify_node(tmp);
-        expr.swap(tmp);
-        return false;
+        return std::move(tmp);
       }
       else if(truevalue.is_false())
       {
@@ -1379,19 +1369,13 @@ bool simplify_exprt::simplify_if(if_exprt &expr)
         simplify_node(tmp_not_cond);
         and_exprt tmp(tmp_not_cond, falsevalue);
         simplify_node(tmp);
-        expr.swap(tmp);
-        return false;
+        return std::move(tmp);
       }
     }
   }
 
   if(truevalue==falsevalue)
-  {
-    exprt tmp;
-    tmp.swap(truevalue);
-    expr.swap(tmp);
-    return false;
-  }
+    return truevalue;
 
   // this pushes the if-then-else into struct and array constructors
   if(((truevalue.id()==ID_struct && falsevalue.id()==ID_struct) ||
@@ -1409,17 +1393,14 @@ bool simplify_exprt::simplify_if(if_exprt &expr)
 
     for(const auto &pair : range_true.zip(range_false))
     {
-      if_exprt if_expr(cond_copy, pair.first, pair.second);
-      simplify_if(if_expr);
-      new_expr.operands().push_back(std::move(if_expr));
+      new_expr.operands().push_back(
+        simplify_if(if_exprt(cond_copy, pair.first, pair.second)));
     }
 
-    expr.swap(new_expr);
-
-    return false;
+    return std::move(new_expr);
   }
 
-  return result;
+  return unchanged(expr);
 }
 
 bool simplify_exprt::get_values(
@@ -1994,8 +1975,7 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
       simplify_byte_extract(to_byte_extract_expr(if_expr.true_case()));
     if_expr.false_case() =
       simplify_byte_extract(to_byte_extract_expr(if_expr.false_case()));
-    simplify_if(if_expr);
-    return std::move(if_expr);
+    return simplify_if(if_expr);
   }
 
   const auto el_size = pointer_offset_bits(expr.type(), ns);
@@ -2523,7 +2503,14 @@ bool simplify_exprt::simplify_node(exprt &expr)
           expr.id()==ID_ge    || expr.id()==ID_le)
     no_change = simplify_inequality(expr) && no_change;
   else if(expr.id()==ID_if)
-    no_change = simplify_if(to_if_expr(expr)) && no_change;
+  {
+    auto r = simplify_if(to_if_expr(expr));
+    if(r.has_changed())
+    {
+      no_change = false;
+      expr = r.expr;
+    }
+  }
   else if(expr.id()==ID_lambda)
     no_change = simplify_lambda(expr) && no_change;
   else if(expr.id()==ID_with)

src/util/simplify_expr_array.cpp

@@ -102,10 +102,7 @@ bool simplify_exprt::simplify_index(exprt &expr)
       }
 
       if_exprt if_expr(equality_expr, with_expr.new_value(), new_index_expr);
-      simplify_if(if_expr);
-
-      expr.swap(if_expr);
-
+      expr = simplify_if(if_expr).expr;
       return false;
     }
   }

src/util/simplify_expr_class.h

@@ -143,7 +143,7 @@ class simplify_exprt
   NODISCARD resultt<> simplify_power(const exprt &);
   NODISCARD resultt<> simplify_bitwise(const exprt &);
   bool simplify_if_preorder(if_exprt &expr);
-  bool simplify_if(if_exprt &expr);
+  NODISCARD resultt<> simplify_if(const if_exprt &);
   bool simplify_bitnot(exprt &expr);
   bool simplify_not(exprt &expr);
   bool simplify_boolean(exprt &expr);

src/util/simplify_expr_int.cpp

@@ -1261,9 +1261,7 @@ bool simplify_exprt::simplify_inequality(exprt &expr)
     if_exprt if_expr=lift_if(expr, 0);
     simplify_inequality(if_expr.true_case());
     simplify_inequality(if_expr.false_case());
-    simplify_if(if_expr);
-    expr.swap(if_expr);
-
+    expr = simplify_if(if_expr).expr;
     return false;
   }
 
@@ -1640,9 +1638,7 @@ bool simplify_exprt::simplify_inequality_rhs_is_constant(exprt &expr)
     if_exprt if_expr=lift_if(expr, 0);
     simplify_inequality_rhs_is_constant(if_expr.true_case());
     simplify_inequality_rhs_is_constant(if_expr.false_case());
-    simplify_if(if_expr);
-    expr.swap(if_expr);
-
+    expr = simplify_if(if_expr);
     return false;
   }
 

src/util/simplify_expr_pointer.cpp

@@ -243,8 +243,7 @@ simplify_exprt::simplify_pointer_offset(const exprt &expr)
     if_exprt if_expr=lift_if(expr, 0);
     if_expr.true_case() = simplify_pointer_offset(if_expr.true_case());
     if_expr.false_case() = simplify_pointer_offset(if_expr.false_case());
-    simplify_if(if_expr);
-    return if_expr;
+    return changed(simplify_if(if_expr));
   }
 
   if(ptr.type().id()!=ID_pointer)
@@ -577,8 +576,7 @@ simplify_exprt::simplify_is_dynamic_object(const exprt &expr)
     if_exprt if_expr=lift_if(expr, 0);
     if_expr.true_case() = simplify_is_dynamic_object(if_expr.true_case());
     if_expr.false_case() = simplify_is_dynamic_object(if_expr.false_case());
-    simplify_if(if_expr);
-    return std::move(if_expr);
+    return changed(simplify_if(if_expr));
   }
 
   bool no_change = true;