Add a swap implementation that works on all backend.

Calling std::swap isn't legal from CUDA code, but the new vtkm::Swap
method is safe. It currently does a naive swap when compiling CUDA
code, and falls back to an ADL swap

docs/changelog/swap.md

@@ -0,0 +1,7 @@
+# Add a CUDA-safe `vtkm::Swap` method.
+
+Added a swap implementation that is safe to call from all backends.
+
+It is not legal to call std functions from CUDA code, and the new
+`vtkm::Swap` implements a naive swap when compiled under NVCC while
+falling back to a std/ADL swap otherwise.

vtkm/CMakeLists.txt

@@ -46,6 +46,7 @@ set(headers
   RangeId.h
   RangeId3.h
   StaticAssert.h
+  Swap.h
   TopologyElementTag.h
   Transform3D.h
   TypeListTag.h

vtkm/Swap.h

@@ -0,0 +1,51 @@
+//============================================================================
+//  Copyright (c) Kitware, Inc.
+//  All rights reserved.
+//  See LICENSE.txt for details.
+//  This software is distributed WITHOUT ANY WARRANTY; without even
+//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+//  PURPOSE.  See the above copyright notice for more information.
+//
+//  Copyright 2018 National Technology & Engineering Solutions of Sandia, LLC (NTESS).
+//  Copyright 2018 UT-Battelle, LLC.
+//  Copyright 2018 Los Alamos National Security.
+//
+//  Under the terms of Contract DE-NA0003525 with NTESS,
+//  the U.S. Government retains certain rights in this software.
+//
+//  Under the terms of Contract DE-AC52-06NA25396 with Los Alamos National
+//  Laboratory (LANL), the U.S. Government retains certain rights in
+//  this software.
+//============================================================================
+
+#ifndef vtk_m_Swap_h
+#define vtk_m_Swap_h
+
+#include <vtkm/internal/ExportMacros.h>
+
+#include <algorithm>
+
+namespace vtkm
+{
+
+/// Performs a swap operation. Safe to call from cuda code.
+#ifdef __CUDACC__
+template <typename T>
+VTKM_EXEC_CONT void Swap(T& a, T& b)
+{
+  T tmp = a;
+  a = b;
+  b = tmp;
+}
+#else
+template <typename T>
+VTKM_EXEC_CONT void Swap(T& a, T& b)
+{
+  using namespace std;
+  swap(a, b);
+}
+#endif
+
+} // end namespace vtkm
+
+#endif //vtk_m_Swap_h

vtkm/rendering/Wireframer.h

@@ -23,6 +23,7 @@
 
 #include <vtkm/Assert.h>
 #include <vtkm/Math.h>
+#include <vtkm/Swap.h>
 #include <vtkm/Types.h>
 #include <vtkm/VectorAnalysis.h>
 #include <vtkm/cont/ArrayHandle.h>
@@ -219,16 +220,16 @@ public:
     bool transposed = vtkm::Abs(y2 - y1) > vtkm::Abs(x2 - x1);
     if (transposed)
     {
-      std::swap(x1, y1);
-      std::swap(x2, y2);
+      vtkm::Swap(x1, y1);
+      vtkm::Swap(x2, y2);
     }
 
     // Ensure we are always going from left to right
     if (x1 > x2)
     {
-      std::swap(x1, x2);
-      std::swap(y1, y2);
-      std::swap(z1, z2);
+      vtkm::Swap(x1, x2);
+      vtkm::Swap(y1, y2);
+      vtkm::Swap(z1, z2);
     }
 
     vtkm::Float32 dx = x2 - x1;