Implemented flyspray request 1041 with patch by Steffen.

Improved it such that placement new is only called when necessary.

[[Imported from SVN: r1757]]

COPYING

@@ -15,6 +15,7 @@ Copyright holders:
 2009--2012    Andreas Lauser
 2012          Tobias Malkmus
 2007--2009    Sven Marnach
+2013          Steffen Müthing
 2003--2005    Thimo Neubauer
 2010--2012    Rebecca Neumann
 2012          Andreas Nüßing

dune/istl/bcrsmatrix.hh

@@ -14,6 +14,7 @@
 
 #include "istlexception.hh"
 #include "bvector.hh"
+#include "matrixutils.hh"
 #include <dune/common/shared_ptr.hh>
 #include <dune/common/stdstreams.hh>
 #include <dune/common/iteratorfacades.hh>
@@ -633,9 +634,11 @@ namespace Dune {
             // memory is allocated individually per row
             // allocate and set row i
             B*   a = Mat.allocator_.allocate(s);
-            new (a) B[s];
+            if(!MatrixHasTrivialConstructor<B>::value)
+              // use placement new to call constructor that allocates
+              // additional memory.
+              new (a) B[s];
             size_type* j = Mat.sizeAllocator_.allocate(s);
-            new (j) size_type[s];
             Mat.r[i].set(s,a,j);
           }
         }else
@@ -1414,7 +1417,6 @@ namespace Dune {
       if(allocateRows) {
         if (n>0) {
           r = rowAllocator_.allocate(rows);
-          new (r) row_type[rows];
         }else{
           r = 0;
         }
@@ -1424,6 +1426,11 @@ namespace Dune {
       // allocate a and j array
       if (nnz>0) {
         a = allocator_.allocate(nnz);
+        if(!MatrixHasTrivialConstructor<B>::value)
+          // use placement new to call constructor that allocates
+          // additional memory.
+          new (a) B[nnz];
+
         // allocate column indices only if not yet present (enable sharing)
         if (!j.get())
           j.reset(sizeAllocator_.allocate(nnz),Deallocator(sizeAllocator_));

dune/istl/matrixutils.hh

@@ -480,6 +480,26 @@ namespace Dune
       value = true
     };
   };
+  //! \brief TMP telling whether a matrix type hase a trivial constructor.
+  //!
+  //! We call a constructor trivial if we can already a assign value
+  //! to a matrix once memory for it is allocated. That is, the
+  //! constructor may not allocate any additional memory.
+  //! \tparam The type of the matrix
+  template<typename M>
+  struct MatrixHasTrivialConstructor
+  {
+    enum {
+      //! \brief Whether this matrix has a trivial constructor
+      value=0
+    };
+  };
+
+  template<typename B, int n, int m>
+  struct MatrixHasTrivialConstructor<FieldMatrix<B,n,m> >
+  {
+    enum {value=1};
 
+  };
 }
 #endif