Add construct_at, destroy_at wrappers. Use throughout.

Eigen/src/Core/CoreEvaluators.h

@@ -1723,14 +1723,14 @@ struct evaluator<EvalToTemp<ArgType> >
   EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr)
     : m_result(xpr.arg())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
   }
 
   // This constructor is used when nesting an EvalTo evaluator in another evaluator
   EIGEN_DEVICE_FUNC evaluator(const ArgType& arg)
     : m_result(arg)
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
   }
 
 protected:

Eigen/src/Core/Inverse.h

@@ -104,7 +104,7 @@ struct unary_evaluator<Inverse<ArgType> >
   unary_evaluator(const InverseType& inv_xpr)
     : m_result(inv_xpr.rows(), inv_xpr.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     internal::call_assignment_no_alias(m_result, inv_xpr);
   }
 

Eigen/src/Core/ProductEvaluators.h

@@ -109,7 +109,7 @@ struct product_evaluator<Product<Lhs, Rhs, Options>, ProductTag, LhsShape, RhsSh
   explicit product_evaluator(const XprType& xpr)
     : m_result(xpr.rows(), xpr.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
 
 // FIXME shall we handle nested_eval here?,
 // if so, then we must take care at removing the call to nested_eval in the specializations (e.g., in permutation_matrix_product, transposition_matrix_product, etc.)

Eigen/src/Core/Ref.h

@@ -199,8 +199,8 @@ protected:
       return false;
     }
 
-    ::new (static_cast<Base*>(this)) Base(expr.data(), rows, cols);
+    internal::construct_at<Base>(this, expr.data(), rows, cols);
-    ::new (&m_stride) StrideBase(
+    internal::construct_at(&m_stride,
       (StrideType::OuterStrideAtCompileTime == 0) ? 0 : outer_stride,
       (StrideType::InnerStrideAtCompileTime == 0) ? 0 : inner_stride );
     return true;

Eigen/src/Core/ReturnByValue.h

@@ -106,7 +106,7 @@ struct evaluator<ReturnByValue<Derived> >
   EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr)
     : m_result(xpr.rows(), xpr.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     xpr.evalTo(m_result);
   }
 

Eigen/src/Core/Solve.h

@@ -125,7 +125,7 @@ struct evaluator<Solve<Decomposition,RhsType> >
   EIGEN_DEVICE_FUNC explicit evaluator(const SolveType& solve)
     : m_result(solve.rows(), solve.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     solve.dec()._solve_impl(solve.rhs(), m_result);
   }
 

Eigen/src/Core/util/Memory.h

@@ -1150,6 +1150,38 @@ inline int queryTopLevelCacheSize()
   return (std::max)(l2,l3);
 }
 
+
+
+/** \internal
+ * This wraps C++20's std::construct_at, using placement new instead if it is not available.
+ */
+
+#if EIGEN_COMP_CXXVER >= 20
+using std::construct_at;
+#else
+template<class T, class... Args>
+T* construct_at( T* p, Args&&... args )
+{
+  return ::new (const_cast<void*>(static_cast<const volatile void*>(p)))
+    T(std::forward<Args>(args)...);
+}
+#endif
+
+/** \internal
+ * This wraps C++17's std::destroy_at.  If it's not available it calls the destructor.
+ * The wrapper is not a full replacement for C++20's std::destroy_at as it cannot
+ * be applied to std::array.
+ */
+#if EIGEN_COMP_CXXVER >= 17
+using std::destroy_at;
+#else
+template<class T>
+void destroy_at(T* p)
+{
+  p->~T();
+}
+#endif
+
 } // end namespace internal
 
 } // end namespace Eigen

Eigen/src/Geometry/Homogeneous.h

@@ -345,7 +345,7 @@ struct unary_evaluator<Homogeneous<ArgType,Direction>, IndexBased>
   EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& op)
     : Base(), m_temp(op)
   {
-    ::new (static_cast<Base*>(this)) Base(m_temp);
+    internal::construct_at<Base>(this, m_temp);
   }
 
 protected:

Eigen/src/IterativeLinearSolvers/IterativeSolverBase.h

@@ -79,16 +79,16 @@ public:
   template<typename MatrixDerived>
   void grab(const EigenBase<MatrixDerived> &mat)
   {
-    m_matrix.~Ref<const MatrixType>();
+    internal::destroy_at(&m_matrix);
-    ::new (&m_matrix) Ref<const MatrixType>(mat.derived());
+    internal::construct_at(&m_matrix, mat.derived());
   }
 
   void grab(const Ref<const MatrixType> &mat)
   {
     if(&(mat.derived()) != &m_matrix)
     {
-      m_matrix.~Ref<const MatrixType>();
+      internal::destroy_at(&m_matrix);
-      ::new (&m_matrix) Ref<const MatrixType>(mat);
+      internal::construct_at(&m_matrix, mat);
     }
   }
 

Eigen/src/IterativeLinearSolvers/SolveWithGuess.h

@@ -85,7 +85,7 @@ struct evaluator<SolveWithGuess<Decomposition,RhsType, GuessType> >
   evaluator(const SolveType& solve)
     : m_result(solve.rows(), solve.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     m_result = solve.guess();
     solve.dec()._solve_with_guess_impl(solve.rhs(), m_result);
   }

Eigen/src/KLUSupport/KLUSupport.h

@@ -265,16 +265,16 @@ class KLU : public SparseSolverBase<KLU<MatrixType_> >
     template<typename MatrixDerived>
     void grab(const EigenBase<MatrixDerived> &A)
     {
-      mp_matrix.~KLUMatrixRef();
+      internal::destroy_at(&mp_matrix);
-      ::new (&mp_matrix) KLUMatrixRef(A.derived());
+      internal::construct_at(&mp_matrix, A.derived());
     }
 
     void grab(const KLUMatrixRef &A)
     {
       if(&(A.derived()) != &mp_matrix)
       {
-        mp_matrix.~KLUMatrixRef();
+        internal::destroy_at(&mp_matrix);
-        ::new (&mp_matrix) KLUMatrixRef(A);
+        internal::construct_at(&mp_matrix, A);
       }
     }
 

Eigen/src/SVD/JacobiSVD.h

@@ -73,8 +73,8 @@ class qr_preconditioner_impl<MatrixType, Options, FullPivHouseholderQRPreconditi
   void allocate(const SVDType& svd) {
     if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.rows(), svd.cols());
+      internal::construct_at(&m_qr, svd.rows(), svd.cols());
     }
     if (svd.m_computeFullU) m_workspace.resize(svd.rows());
   }
@@ -119,8 +119,8 @@ class qr_preconditioner_impl<MatrixType, Options, FullPivHouseholderQRPreconditi
   void allocate(const SVDType& svd) {
     if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.cols(), svd.rows());
+      internal::construct_at(&m_qr, svd.cols(), svd.rows());
     }
     m_adjoint.resize(svd.cols(), svd.rows());
     if (svd.m_computeFullV) m_workspace.resize(svd.cols());
@@ -165,8 +165,8 @@ class qr_preconditioner_impl<MatrixType, Options, ColPivHouseholderQRPreconditio
   void allocate(const SVDType& svd) {
     if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.rows(), svd.cols());
+      internal::construct_at(&m_qr, svd.rows(), svd.cols());
     }
     if (svd.m_computeFullU) m_workspace.resize(svd.rows());
     else if (svd.m_computeThinU) m_workspace.resize(svd.cols());
@@ -221,8 +221,8 @@ class qr_preconditioner_impl<MatrixType, Options, ColPivHouseholderQRPreconditio
   void allocate(const SVDType& svd) {
     if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.cols(), svd.rows());
+      internal::construct_at(&m_qr, svd.cols(), svd.rows());
     }
     if (svd.m_computeFullV) m_workspace.resize(svd.cols());
     else if (svd.m_computeThinV) m_workspace.resize(svd.rows());
@@ -273,8 +273,8 @@ class qr_preconditioner_impl<MatrixType, Options, HouseholderQRPreconditioner, P
   void allocate(const SVDType& svd) {
     if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.rows(), svd.cols());
+      internal::construct_at(&m_qr, svd.rows(), svd.cols());
     }
     if (svd.m_computeFullU) m_workspace.resize(svd.rows());
     else if (svd.m_computeThinU) m_workspace.resize(svd.cols());
@@ -328,8 +328,8 @@ class qr_preconditioner_impl<MatrixType, Options, HouseholderQRPreconditioner, P
   void allocate(const SVDType& svd) {
     if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
     {
-      m_qr.~QRType();
+      internal::destroy_at(&m_qr);
-      ::new (&m_qr) QRType(svd.cols(), svd.rows());
+      internal::construct_at(&m_qr, svd.cols(), svd.rows());
     }
     if (svd.m_computeFullV) m_workspace.resize(svd.cols());
     else if (svd.m_computeThinV) m_workspace.resize(svd.rows());

Eigen/src/SparseCore/SparseBlock.h

@@ -535,8 +535,8 @@ public:
     while(++m_outerPos<m_end)
     {
       // Restart iterator at the next inner-vector:
-      m_it.~EvalIterator();
+      internal::destroy_at(&m_it);
-      ::new (&m_it) EvalIterator(m_eval.m_argImpl, m_outerPos);
+      internal::construct_at(&m_it, m_eval.m_argImpl, m_outerPos);
       // search for the key m_innerIndex in the current outer-vector
       while(m_it && m_it.index() < m_innerIndex) ++m_it;
       if(m_it && m_it.index()==m_innerIndex) break;

Eigen/src/SparseCore/SparsePermutation.h

@@ -109,7 +109,7 @@ struct product_evaluator<Product<Lhs, Rhs, AliasFreeProduct>, ProductTag, Permut
   explicit product_evaluator(const XprType& xpr)
     : m_result(xpr.rows(), xpr.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     generic_product_impl<Lhs, Rhs, PermutationShape, SparseShape, ProductTag>::evalTo(m_result, xpr.lhs(), xpr.rhs());
   }
 

Eigen/src/SparseCore/SparseProduct.h

@@ -149,7 +149,7 @@ struct unary_evaluator<SparseView<Product<Lhs, Rhs, Options> >, IteratorBased>
     : m_result(xpr.rows(), xpr.cols())
   {
     using std::abs;
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     typedef typename nested_eval<Lhs,Dynamic>::type LhsNested;
     typedef typename nested_eval<Rhs,Dynamic>::type RhsNested;
     LhsNested lhsNested(xpr.nestedExpression().lhs());

Eigen/src/SparseCore/SparseRef.h

@@ -100,9 +100,9 @@ protected:
   void construct(Expression& expr)
   {
     if(expr.outerIndexPtr()==0)
-      ::new (static_cast<Base*>(this)) Base(expr.size(), expr.nonZeros(), expr.innerIndexPtr(), expr.valuePtr());
+      internal::construct_at<Base>(this, expr.size(), expr.nonZeros(), expr.innerIndexPtr(), expr.valuePtr());
     else
-      ::new (static_cast<Base*>(this)) Base(expr.rows(), expr.cols(), expr.nonZeros(), expr.outerIndexPtr(), expr.innerIndexPtr(), expr.valuePtr(), expr.innerNonZeroPtr());
+      internal::construct_at<Base>(this, expr.rows(), expr.cols(), expr.nonZeros(), expr.outerIndexPtr(), expr.innerIndexPtr(), expr.valuePtr(), expr.innerNonZeroPtr());
   }
 };
 
@@ -203,8 +203,7 @@ class Ref<const SparseMatrix<MatScalar,MatOptions,MatIndex>, Options, StrideType
 
     ~Ref() {
       if(m_hasCopy) {
-        TPlainObjectType* obj = reinterpret_cast<TPlainObjectType*>(&m_storage);
+        internal::destroy_at(reinterpret_cast<TPlainObjectType*>(&m_storage));
-        obj->~TPlainObjectType();
       }
     }
 
@@ -215,8 +214,7 @@ class Ref<const SparseMatrix<MatScalar,MatOptions,MatIndex>, Options, StrideType
     {
       if((Options & int(StandardCompressedFormat)) && (!expr.isCompressed()))
       {
-        TPlainObjectType* obj = reinterpret_cast<TPlainObjectType*>(&m_storage);
+        TPlainObjectType* obj = internal::construct_at(reinterpret_cast<TPlainObjectType*>(&m_storage), expr);
-        ::new (obj) TPlainObjectType(expr);
         m_hasCopy = true;
         Base::construct(*obj);
       }
@@ -229,8 +227,7 @@ class Ref<const SparseMatrix<MatScalar,MatOptions,MatIndex>, Options, StrideType
     template<typename Expression>
     void construct(const Expression& expr, internal::false_type)
     {
-      TPlainObjectType* obj = reinterpret_cast<TPlainObjectType*>(&m_storage);
+      TPlainObjectType* obj = internal::construct_at(reinterpret_cast<TPlainObjectType*>(&m_storage), expr);
-      ::new (obj) TPlainObjectType(expr);
       m_hasCopy = true;
       Base::construct(*obj);
     }
@@ -321,8 +318,7 @@ class Ref<const SparseVector<MatScalar,MatOptions,MatIndex>, Options, StrideType
 
     ~Ref() {
       if(m_hasCopy) {
-        TPlainObjectType* obj = reinterpret_cast<TPlainObjectType*>(&m_storage);
+        internal::destroy_at(reinterpret_cast<TPlainObjectType*>(&m_storage));
-        obj->~TPlainObjectType();
       }
     }
 
@@ -337,8 +333,7 @@ class Ref<const SparseVector<MatScalar,MatOptions,MatIndex>, Options, StrideType
     template<typename Expression>
     void construct(const Expression& expr, internal::false_type)
     {
-      TPlainObjectType* obj = reinterpret_cast<TPlainObjectType*>(&m_storage);
+      TPlainObjectType* obj = internal::construct_at(reinterpret_cast<TPlainObjectType*>(&m_storage), expr);
-      ::new (obj) TPlainObjectType(expr);
       m_hasCopy = true;
       Base::construct(*obj);
     }

Eigen/src/SparseCore/SparseSelfAdjointView.h

@@ -383,7 +383,7 @@ struct product_evaluator<Product<LhsView, Rhs, DefaultProduct>, ProductTag, Spar
   product_evaluator(const XprType& xpr)
     : m_lhs(xpr.lhs()), m_result(xpr.rows(), xpr.cols())
   {
-    ::new (static_cast<Base*>(this)) Base(m_result);
+    internal::construct_at<Base>(this, m_result);
     generic_product_impl<typename Rhs::PlainObject, Rhs, SparseShape, SparseShape, ProductTag>::evalTo(m_result, m_lhs, xpr.rhs());
   }
   

Eigen/src/UmfPackSupport/UmfPackSupport.h

@@ -531,16 +531,16 @@ class UmfPackLU : public SparseSolverBase<UmfPackLU<MatrixType_> >
     template<typename MatrixDerived>
     void grab(const EigenBase<MatrixDerived> &A)
     {
-      mp_matrix.~UmfpackMatrixRef();
+      internal::destroy_at(&mp_matrix);
-      ::new (&mp_matrix) UmfpackMatrixRef(A.derived());
+      internal::construct_at(&mp_matrix, A.derived());
     }
 
     void grab(const UmfpackMatrixRef &A)
     {
       if(&(A.derived()) != &mp_matrix)
       {
-        mp_matrix.~UmfpackMatrixRef();
+        internal::destroy_at(&mp_matrix);
-        ::new (&mp_matrix) UmfpackMatrixRef(A);
+        internal::construct_at(&mp_matrix, A);
       }
     }