Ensure that Pair and Vec are trivial classes.

For std::copy to optimize a copy to memcpy, the valuetype must be both
trivially constructable and trivially copyable.

The new copy benchmarks highlighted an issue that std::copy'ing pairs
and vecs were not optimized to memcpy. For a 256 MiB buffer on my
laptop w/ GCC, the serial copy speeds were:

UInt8:                 10.10 GiB/s
Vec<UInt8, 2>           3.12 GiB/s
Pair<UInt32, Float32>   6.92 GiB/s

After this patch, the optimization occurs and a bitwise copy occurs:

UInt8:                 10.12 GiB/s
Vec<UInt8, 2>           9.66 GiB/s
Pair<UInt32, Float32>   9.88 GiB/s

Check were also added to the Vec and Pair unit tests to ensure that
this classes continue to be trivial.

The ArrayHandleSwizzle test was refactored a bit to eliminate a new
'possibly uninitialized memory' warning introduced with the default
Vec ctors.

vtkm/Pair.h

@@ -65,11 +65,7 @@ struct Pair
   SecondType second;
 
   VTKM_EXEC_CONT
-  Pair()
-    : first()
-    , second()
-  {
-  }
+  Pair() = default;
 
   VTKM_EXEC_CONT
   Pair(const FirstType& firstSrc, const SecondType& secondSrc)
@@ -93,12 +89,8 @@ struct Pair
   }
 
   VTKM_EXEC_CONT
-  vtkm::Pair<FirstType, SecondType>& operator=(const vtkm::Pair<FirstType, SecondType>& src)
-  {
-    this->first = src.first;
-    this->second = src.second;
-    return *this;
-  }
+  vtkm::Pair<FirstType, SecondType>& operator=(const vtkm::Pair<FirstType, SecondType>& src) =
+    default;
 
   VTKM_EXEC_CONT
   bool operator==(const vtkm::Pair<FirstType, SecondType>& other) const

vtkm/Types.h

@@ -438,7 +438,7 @@ public:
 
 protected:
   VTKM_EXEC_CONT
-  VecBaseCommon() {}
+  VecBaseCommon() = default;
 
   VTKM_EXEC_CONT
   const DerivedClass& Derived() const { return *static_cast<const DerivedClass*>(this); }
@@ -666,7 +666,7 @@ public:
 
 protected:
   VTKM_EXEC_CONT
-  VecBase() {}
+  VecBase() = default;
 
   VTKM_EXEC_CONT
   explicit VecBase(const ComponentType& value)
@@ -824,7 +824,7 @@ public:
   static const vtkm::IdComponent NUM_COMPONENTS = Size;
 #endif
 
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const T& value)
     : Superclass(value)
   {
@@ -851,7 +851,7 @@ public:
   using ComponentType = T;
   static const vtkm::IdComponent NUM_COMPONENTS = 0;
 
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const ComponentType&) {}
 
   template <typename OtherType>
@@ -882,7 +882,7 @@ class VTKM_ALWAYS_EXPORT Vec<T, 1> : public detail::VecBase<T, 1, Vec<T, 1>>
   using Superclass = detail::VecBase<T, 1, Vec<T, 1>>;
 
 public:
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const T& value)
     : Superclass(value)
   {
@@ -912,7 +912,7 @@ class VTKM_ALWAYS_EXPORT Vec<T, 2> : public detail::VecBase<T, 2, Vec<T, 2>>
   using Superclass = detail::VecBase<T, 2, Vec<T, 2>>;
 
 public:
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const T& value)
     : Superclass(value)
   {
@@ -941,7 +941,7 @@ class VTKM_ALWAYS_EXPORT Vec<T, 3> : public detail::VecBase<T, 3, Vec<T, 3>>
   using Superclass = detail::VecBase<T, 3, Vec<T, 3>>;
 
 public:
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const T& value)
     : Superclass(value)
   {
@@ -972,7 +972,7 @@ class VTKM_ALWAYS_EXPORT Vec<T, 4> : public detail::VecBase<T, 4, Vec<T, 4>>
   using Superclass = detail::VecBase<T, 4, Vec<T, 4>>;
 
 public:
-  VTKM_EXEC_CONT Vec() {}
+  VTKM_EXEC_CONT Vec() = default;
   VTKM_EXEC_CONT explicit Vec(const T& value)
     : Superclass(value)
   {

vtkm/cont/testing/UnitTestArrayHandleSwizzle.cxx

@@ -141,12 +141,12 @@ struct SwizzleTests
     auto refPortal = this->RefArray.GetPortalConstControl();
     auto testPortal = testArray.GetPortalConstControl();
 
+    SwizzleVectorType refVecSwizzle(vtkm::TypeTraits<SwizzleVectorType>::ZeroInitialization());
     for (vtkm::Id i = 0; i < testArray.GetNumberOfValues(); ++i)
     {
-      // Manually swizzle the reference vector using the runtime map information:
       ReferenceVectorType refVec = refPortal.Get(i);
-      SwizzleVectorType refVecSwizzle;
 
+      // Manually swizzle the reference vector using the runtime map information:
       for (size_t j = 0; j < map.size(); ++j)
       {
         refVecSwizzle[static_cast<vtkm::IdComponent>(j)] = refVec[map[j]];

vtkm/testing/UnitTestPair.cxx

@@ -31,6 +31,16 @@ namespace
 template <typename T, typename U>
 void PairTest()
 {
+  {
+    using P = vtkm::Pair<T, U>;
+
+    // Pair types should preserve the trivial properties of their components.
+    // This insures that algorithms like std::copy will optimize fully.
+    VTKM_TEST_ASSERT(std::is_trivial<T>::value &&
+                       std::is_trivial<U>::value == std::is_trivial<P>::value,
+                     "PairType's triviality differs from ComponentTypes.");
+  }
+
   //test that all the constructors work properly
   {
     vtkm::Pair<T, U> no_params_pair;

vtkm/testing/UnitTestTypes.cxx

@@ -323,6 +323,11 @@ void GeneralVecTypeTest(const vtkm::Vec<ComponentType, Size>&)
 
   typedef vtkm::Vec<ComponentType, Size> T;
 
+  // Vector types should preserve the trivial properties of their components.
+  // This insures that algorithms like std::copy will optimize fully.
+  VTKM_TEST_ASSERT(std::is_trivial<ComponentType>::value == std::is_trivial<T>::value,
+                   "VectorType's triviality differs from ComponentType.");
+
   VTKM_TEST_ASSERT(T::NUM_COMPONENTS == Size, "NUM_COMPONENTS is wrong size.");
 
   //grab the number of elements of T