From ec0791e941d1be0bc2befe2e43b953dc19e03cc0 Mon Sep 17 00:00:00 2001
From: Allison Vacanti <allison.vacanti@kitware.com>
Date: Fri, 1 Jun 2018 14:01:23 -0400
Subject: [PATCH] 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      |  7 +++++
 vtkm/CMakeLists.txt         |  1 +
 vtkm/Swap.h                 | 51 +++++++++++++++++++++++++++++++++++++
 vtkm/rendering/Wireframer.h | 11 ++++----
 4 files changed, 65 insertions(+), 5 deletions(-)
 create mode 100644 docs/changelog/swap.md
 create mode 100644 vtkm/Swap.h

diff --git a/docs/changelog/swap.md b/docs/changelog/swap.md
new file mode 100644
index 000000000..cd1822c76
--- /dev/null
+++ b/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.
diff --git a/vtkm/CMakeLists.txt b/vtkm/CMakeLists.txt
index 4ecb43234..be9ff8b80 100644
--- a/vtkm/CMakeLists.txt
+++ b/vtkm/CMakeLists.txt
@@ -46,6 +46,7 @@ set(headers
   RangeId.h
   RangeId3.h
   StaticAssert.h
+  Swap.h
   TopologyElementTag.h
   Transform3D.h
   TypeListTag.h
diff --git a/vtkm/Swap.h b/vtkm/Swap.h
new file mode 100644
index 000000000..b870248d0
--- /dev/null
+++ b/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
diff --git a/vtkm/rendering/Wireframer.h b/vtkm/rendering/Wireframer.h
index 43cb767ed..ba3d977a7 100644
--- a/vtkm/rendering/Wireframer.h
+++ b/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;