From 093b191dbcf54b0860ac55b9705e5d9c1c6ec05c Mon Sep 17 00:00:00 2001
From: Gleb Belov <gleb@ampl.com>
Date: Mon, 28 Oct 2024 12:25:09 +1100
Subject: [PATCH] MP2NL: reuse explicified exprs #237

---
 include/mp/flat/constr_keeper.h          |  8 ++++++++
 include/mp/flat/nl_expr/model_api_base.h | 22 ++++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/include/mp/flat/constr_keeper.h b/include/mp/flat/constr_keeper.h
index ce2e32b0a..19c4a96f3 100644
--- a/include/mp/flat/constr_keeper.h
+++ b/include/mp/flat/constr_keeper.h
@@ -263,6 +263,8 @@ class ConstraintKeeper final
     if constexpr (ExpressionAcceptanceLevel::NotAccepted
         != Backend::ExpressionInterfaceAcceptanceLevel()) {
       assert(!cons_[i].IsBridged());
+      assert(!cons_[i].IsExprAdded());
+      cons_[i].MarkExprAdded();
       *(typename Backend::Expr*)pexpr =
           static_cast<Backend&>(be).AddExpression(cons_[i].GetExpr());
     }
@@ -319,6 +321,11 @@ class ConstraintKeeper final
       is_unused_=true;
     }
 
+    /// Has the expression been added to the backend?
+    bool IsExprAdded() const { return is_expr_stored_; }
+    /// Mark as added
+    void MarkExprAdded() { is_expr_stored_=true; }
+
     /// Get the flat constraint, const &
     const Constraint& GetCon() const { return con_.GetFlatConstraint(); }
     /// Get the flat constraint &
@@ -336,6 +343,7 @@ class ConstraintKeeper final
     int depth_ = 0;
     bool is_bridged_ = false;
     bool is_unused_ = false;
+    bool is_expr_stored_ = false;
   };
 
 	/// Convert all new constraints of this type
diff --git a/include/mp/flat/nl_expr/model_api_base.h b/include/mp/flat/nl_expr/model_api_base.h
index ad911c36e..be7edd6ab 100644
--- a/include/mp/flat/nl_expr/model_api_base.h
+++ b/include/mp/flat/nl_expr/model_api_base.h
@@ -323,9 +323,11 @@ class BasicExprModelAPI
     assert(!is_init_expr_retrieved_[i_expr]);             // not twice explicified
     if (IsVarProper(i_expr)) {
       is_init_expr_retrieved_[i_expr] = true;             // is being explicified
-      Expr result;
-      get_init_expr_(i_expr, &result);    // TODO we are not caching them.
-      return result;
+      if (!is_init_expr_stored_[i_expr]) {
+        is_init_expr_stored_[i_expr] = true;
+          get_init_expr_(i_expr, &init_expr_stored_[i_expr]);
+      }
+      return init_expr_stored_[i_expr];  // ...............
     }
     return GetInitExpression(i_expr);                     // standard case
   }
@@ -350,6 +352,8 @@ class BasicExprModelAPI
     is_expr_stored_.resize(is_var_proper_.size());    // allocate
     expr_stored_.resize(is_var_proper_.size());
     is_init_expr_retrieved_.resize(is_var_proper_.size());
+    is_init_expr_stored_.resize(is_var_proper_.size());
+    init_expr_stored_.resize(is_var_proper_.size());
   }
 
   /// Is var proper?
@@ -378,10 +382,20 @@ class BasicExprModelAPI
 
 private:
   std::vector<bool> is_var_proper_;
-  std::vector<bool> is_expr_stored_;    // actual Expr's of the result var or the init expressions
+  /// actual Expr's of the result vars (for explicified exprds)
+  /// or the expressions, otherwise
+  std::vector<bool> is_expr_stored_;
   /// Expression cache
   std::deque<ExprType> expr_stored_;    // to keep iterators valid
+
+  /// init exprs: for explicified expressions, whether
+  /// the actual init expr-s retrieved.
+  /// Should be cleared by ResetIniExpr...
+  /// if retrieving repeatedly.
   std::vector<bool> is_init_expr_retrieved_;
+  std::vector<bool> is_init_expr_stored_;
+  /// Expression cache
+  std::deque<ExprType> init_expr_stored_;    // to keep iterators valid
   InitExprGetterType get_init_expr_;
 };