Fix default BoolExpr accumulator construction

changelog.in

@@ -75,6 +75,17 @@ This release modernizes the Gecode build infrastructure, adds a
 first-class CMake package for downstream consumers, refreshes the
 autoconf build path, and updates CI coverage for current platforms.
 
+[ENTRY]
+Module: minimodel
+What:   bug
+Rank:   minor
+Issue:  139
+Thanks: yuri@FreeBSD
+[DESCRIPTION]
+Fix default-constructed Boolean expressions so they can be used as
+empty accumulators for conjunction and disjunction without reading
+uninitialized node state.
+
 [ENTRY]
 Module: float
 What:   bug

gecode/minimodel/bool-expr.cpp

@@ -84,7 +84,7 @@ namespace Gecode {
    *
    */
   BoolExpr::Node::Node(void)
-    : use(1), l(nullptr), r(nullptr), m(nullptr) {}
+    : use(1), same(0), t(NT_AND), l(nullptr), r(nullptr), m(nullptr) {}
 
   BoolExpr::Node::~Node(void) {
     delete m;
@@ -125,8 +125,18 @@ namespace Gecode {
     n->x    = x;
   }
 
-  BoolExpr::BoolExpr(const BoolExpr& l, NodeType t, const BoolExpr& r)
-    : n(new Node) {
+  BoolExpr::BoolExpr(const BoolExpr& l, NodeType t, const BoolExpr& r) {
+    if (((t == NT_AND) || (t == NT_OR)) && (l.n->same == 0)) {
+      n = r.n;
+      n->use++;
+      return;
+    }
+    if (((t == NT_AND) || (t == NT_OR)) && (r.n->same == 0)) {
+      n = l.n;
+      n->use++;
+      return;
+    }
+    n = new Node;
     int ls = ((l.n->t == t) || (l.n->t == NT_VAR)) ? l.n->same : 1;
     int rs = ((r.n->t == t) || (r.n->t == NT_VAR)) ? r.n->same : 1;
     n->same = ls+rs;
@@ -140,7 +150,10 @@ namespace Gecode {
   BoolExpr::BoolExpr(const BoolExpr& l, NodeType t) {
     (void) t;
     assert(t == NT_NOT);
-    if (l.n->t == NT_NOT) {
+    if (l.n->same == 0) {
+      n = l.n;
+      n->use++;
+    } else if (l.n->t == NT_NOT) {
       n = l.n->l;
       n->use++;
     } else {
@@ -505,6 +518,8 @@ namespace Gecode {
 
     NNF*
     NNF::nnf(Region& r, Node* n, bool neg) {
+      if (n->same == 0)
+        throw MiniModel::TooFewArguments("BoolExpr");
       switch (n->t) {
       case BoolExpr::NT_VAR:
       case BoolExpr::NT_RLIN:

test/int/mm-bool.cpp

@@ -165,6 +165,41 @@ namespace Test { namespace Int {
        }
      };
 
+     /// %Test Boolean expressions with default-constructed accumulators
+     class BoolExprDefaultAccumulator : public Test {
+     protected:
+       /// Boolean operation to accumulate
+       BoolOpcode o;
+       /// Whether the default expression starts on the right hand side
+       bool rhs;
+     public:
+       /// Create and register test
+       BoolExprDefaultAccumulator(BoolOpcode o0, bool rhs0)
+         : Test("MiniModel::BoolExpr::Default::"+
+                std::string(o0 == BO_AND ? "And" : "Or")+
+                (rhs0 ? "::Rhs" : "::Lhs"),3,0,1), o(o0), rhs(rhs0) {}
+       /// %Test whether \a x is solution
+       virtual bool solution(const Assignment& x) const {
+         int r = (o == BO_AND) ? (x[0] & x[1]) : (x[0] | x[1]);
+         return r == x[2];
+       }
+       /// Post constraint on \a x
+       virtual void post(Gecode::Space& home, Gecode::IntVarArray& x) {
+         using namespace Gecode;
+         Gecode::BoolExpr e;
+         Gecode::BoolExpr x0(channel(home,x[0]));
+         Gecode::BoolExpr x1(channel(home,x[1]));
+         if (o == BO_AND) {
+           e = rhs ? (x0 && e) : (e && x0);
+           e = e && x1;
+         } else {
+           e = rhs ? (x0 || e) : (e || x0);
+           e = e || x1;
+         }
+         rel(home, expr(home,e), IRT_EQ, channel(home,x[2]));
+       }
+     };
+
     const BoolInstr bi000[] = {
       {BO_AND,0,1,0},{BO_AND,2,3,1},{BO_AND,0,1,0},
       {BO_HLT,0,0,0}
@@ -4382,6 +4417,10 @@ namespace Test { namespace Int {
         (void) new BoolElement("Expr::A",0);
         (void) new BoolElement("Expr::B",1);
         (void) new BoolElement("Rel",2);
+        (void) new BoolExprDefaultAccumulator(BO_AND,false);
+        (void) new BoolExprDefaultAccumulator(BO_AND,true);
+        (void) new BoolExprDefaultAccumulator(BO_OR,false);
+        (void) new BoolExprDefaultAccumulator(BO_OR,true);
       }
     };