Modify scalar pzero, ptrue, pselect, and p<binary> operations to avoid memset.

The `memset` function and bitwise manipulation only apply to POD types
that do not require initialization, otherwise resulting in UB. We currently
violate this in `ptrue` and `pzero`, we assume bitmasks for `pselect`, and
bitwise operations are applied byte-by-byte in the generic implementations.

This is causing issues for scalar types that do require initialization
or that contain non-POD info such as pointers (#2201). We either break
them, or force specializations of these functions for custom scalars,
even if they are not vectorized.

Here we modify these functions for scalars only - instead using only
scalar operations:
- `pzero`: `Scalar(0)` for all scalars.
- `ptrue`: `Scalar(1)` for non-trivial scalars, bitset to one bits for trivial scalars.
- `pselect`: ternary select comparing mask to `Scalar(0)` for all scalars
- `pand`, `por`, `pxor`, `pnot`: use operators `&`, `|`, `^`, `~` for all integer or non-trivial scalars, otherwise apply bytewise.

For non-scalar types, the original implementations are used to maintain
compatibility and minimize the number of changes.

Fixes #2201.

Eigen/src/Core/GenericPacketMath.h

@@ -129,6 +129,22 @@ template<typename T> struct packet_traits : default_packet_traits
 
 template<typename T> struct packet_traits<const T> : packet_traits<T> { };
 
+template<typename T> struct unpacket_traits
+{
+  typedef T type;
+  typedef T half;
+  enum
+  {
+    size = 1,
+    alignment = 1,
+    vectorizable = false,
+    masked_load_available=false,
+    masked_store_available=false
+  };
+};
+
+template<typename T> struct unpacket_traits<const T> : unpacket_traits<T> { };
+
 template <typename Src, typename Tgt> struct type_casting_traits {
   enum {
     VectorizedCast = 0,
@@ -154,6 +170,18 @@ struct eigen_packet_wrapper
   T m_val;
 };
 
+
+/** \internal A convenience utility for determining if the type is a scalar.
+ * This is used to enable some generic packet implementations.
+ */
+template<typename Packet>
+struct is_scalar {
+  typedef typename unpacket_traits<Packet>::type Scalar;
+  enum {
+    value = internal::is_same<Packet, Scalar>::value
+  };
+};
+
 /** \internal \returns static_cast<TgtType>(a) (coeff-wise) */
 template <typename SrcPacket, typename TgtPacket>
 EIGEN_DEVICE_FUNC inline TgtPacket
@@ -215,13 +243,59 @@ pmul(const bool& a, const bool& b) { return a && b; }
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 pdiv(const Packet& a, const Packet& b) { return a/b; }
 
-/** \internal \returns one bits */
-template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
-ptrue(const Packet& /*a*/) { Packet b; memset((void*)&b, 0xff, sizeof(b)); return b;}
+// In the generic case, memset to all one bits.
+template<typename Packet, typename EnableIf = void>
+struct ptrue_impl {
+  static EIGEN_DEVICE_FUNC inline Packet run(const Packet& /*a*/){
+    Packet b;
+    memset(static_cast<void*>(&b), 0xff, sizeof(Packet));
+    return b;
+  }
+};
 
-/** \internal \returns zero bits */
+// For non-trivial scalars, set to Scalar(1) (i.e. a non-zero value).
+// Although this is technically not a valid bitmask, the scalar path for pselect
+// uses a comparison to zero, so this should still work in most cases. We don't
+// have another option, since the scalar type requires initialization.
+template<typename T>
+struct ptrue_impl<T, 
+    typename internal::enable_if<is_scalar<T>::value && NumTraits<T>::RequireInitialization>::type > {
+  static EIGEN_DEVICE_FUNC inline T run(const T& /*a*/){
+    return T(1);
+  }
+};
+
+/** \internal \returns one bits. */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
-pzero(const Packet& /*a*/) { Packet b; memset((void*)&b, 0, sizeof(b)); return b;}
+ptrue(const Packet& a) {
+  return ptrue_impl<Packet>::run(a);
+}
+
+// In the general case, memset to zero.
+template<typename Packet, typename EnableIf = void>
+struct pzero_impl {
+  static EIGEN_DEVICE_FUNC inline Packet run(const Packet& /*a*/) {
+    Packet b;
+    memset(static_cast<void*>(&b), 0x00, sizeof(Packet));
+    return b;
+  }
+};
+
+// For scalars, explicitly set to Scalar(0), since the underlying representation
+// for zero may not consist of all-zero bits.
+template<typename T>
+struct pzero_impl<T,
+    typename internal::enable_if<is_scalar<T>::value>::type> {
+  static EIGEN_DEVICE_FUNC inline T run(const T& /*a*/) {
+    return T(0);
+  }
+};
+
+/** \internal \returns packet of zeros */
+template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
+pzero(const Packet& a) {
+  return pzero_impl<Packet>::run(a);
+}
 
 /** \internal \returns a <= b as a bit mask */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
@@ -238,33 +312,6 @@ pcmp_eq(const Packet& a, const Packet& b) { return a==b ? ptrue(a) : pzero(a); }
 /** \internal \returns a < b or a==NaN or b==NaN as a bit mask */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 pcmp_lt_or_nan(const Packet& a, const Packet& b) { return a>=b ? pzero(a) : ptrue(a); }
-template<> EIGEN_DEVICE_FUNC inline float pzero<float>(const float& a) {
-  EIGEN_UNUSED_VARIABLE(a)
-  return 0.f;
-}
-
-template<> EIGEN_DEVICE_FUNC inline double pzero<double>(const double& a) {
-  EIGEN_UNUSED_VARIABLE(a)
-  return 0.;
-}
-
-template <typename RealScalar>
-EIGEN_DEVICE_FUNC inline std::complex<RealScalar> ptrue(const std::complex<RealScalar>& /*a*/) {
-  RealScalar b = ptrue(RealScalar(0));
-  return std::complex<RealScalar>(b, b);
-}
-
-template <typename Packet, typename Op>
-EIGEN_DEVICE_FUNC inline Packet bitwise_helper(const Packet& a, const Packet& b, Op op) {
-  const unsigned char* a_ptr = reinterpret_cast<const unsigned char*>(&a);
-  const unsigned char* b_ptr = reinterpret_cast<const unsigned char*>(&b);
-  Packet c;
-  unsigned char* c_ptr = reinterpret_cast<unsigned char*>(&c);
-  for (size_t i = 0; i < sizeof(Packet); ++i) {
-    *c_ptr++ = op(*a_ptr++, *b_ptr++);
-  }
-  return c;
-}
 
 template<typename T>
 struct bit_and {
@@ -287,42 +334,123 @@ struct bit_xor {
   }
 };
 
+template<typename T>
+struct bit_not {
+  EIGEN_DEVICE_FUNC EIGEN_CONSTEXPR EIGEN_ALWAYS_INLINE T operator()(const T& a) const {
+    return ~a;
+  }
+};
+
+// Use operators &, |, ^, ~.
+template<typename T>
+struct operator_bitwise_helper {
+  EIGEN_DEVICE_FUNC static inline T bitwise_and(const T& a, const T& b) { return bit_and<T>()(a, b); }
+  EIGEN_DEVICE_FUNC static inline T bitwise_or(const T& a, const T& b) { return bit_or<T>()(a, b); }
+  EIGEN_DEVICE_FUNC static inline T bitwise_xor(const T& a, const T& b) { return bit_xor<T>()(a, b); }
+  EIGEN_DEVICE_FUNC static inline T bitwise_not(const T& a) { return bit_not<T>()(a); }
+};
+
+// Apply binary operations byte-by-byte
+template<typename T>
+struct bytewise_bitwise_helper {
+  EIGEN_DEVICE_FUNC static inline T bitwise_and(const T& a, const T& b) {
+    return binary(a, b, bit_and<unsigned char>());
+  }
+  EIGEN_DEVICE_FUNC static inline T bitwise_or(const T& a, const T& b) { 
+    return binary(a, b, bit_or<unsigned char>());
+   }
+  EIGEN_DEVICE_FUNC static inline T bitwise_xor(const T& a, const T& b) {
+    return binary(a, b, bit_xor<unsigned char>());
+  }
+  EIGEN_DEVICE_FUNC static inline T bitwise_not(const T& a) { 
+    return unary(a,bit_not<unsigned char>());
+   }
+  
+ private:
+  template<typename Op>
+  EIGEN_DEVICE_FUNC static inline T unary(const T& a, Op op) {
+    const unsigned char* a_ptr = reinterpret_cast<const unsigned char*>(&a);
+    T c;
+    unsigned char* c_ptr = reinterpret_cast<unsigned char*>(&c);
+    for (size_t i = 0; i < sizeof(T); ++i) {
+      *c_ptr++ = op(*a_ptr++);
+    }
+    return c;
+  }
+
+  template<typename Op>
+  EIGEN_DEVICE_FUNC static inline T binary(const T& a, const T& b, Op op) {
+    const unsigned char* a_ptr = reinterpret_cast<const unsigned char*>(&a);
+    const unsigned char* b_ptr = reinterpret_cast<const unsigned char*>(&b);
+    T c;
+    unsigned char* c_ptr = reinterpret_cast<unsigned char*>(&c);
+    for (size_t i = 0; i < sizeof(T); ++i) {
+      *c_ptr++ = op(*a_ptr++, *b_ptr++);
+    }
+    return c;
+  }
+};
+
+// In the general case, use byte-by-byte manipulation.
+template<typename T, typename EnableIf = void>
+struct bitwise_helper : public bytewise_bitwise_helper<T> {};
+
+// For integers or non-trivial scalars, use binary operators.
+template<typename T>
+struct bitwise_helper<T,
+  typename internal::enable_if<
+    is_scalar<T>::value && (NumTraits<T>::IsInteger || NumTraits<T>::RequireInitialization)>::type
+  > : public operator_bitwise_helper<T> {};
+
 /** \internal \returns the bitwise and of \a a and \a b */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 pand(const Packet& a, const Packet& b) {
-  return bitwise_helper(a, b, bit_and<unsigned char>());
+  return bitwise_helper<Packet>::bitwise_and(a, b);
 }
 
 /** \internal \returns the bitwise or of \a a and \a b */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 por(const Packet& a, const Packet& b) {
-  return bitwise_helper(a ,b, bit_or<unsigned char>());
+  return bitwise_helper<Packet>::bitwise_or(a, b);
 }
 
 /** \internal \returns the bitwise xor of \a a and \a b */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 pxor(const Packet& a, const Packet& b) {
-  return bitwise_helper(a ,b, bit_xor<unsigned char>());
+  return bitwise_helper<Packet>::bitwise_xor(a, b);
+}
+
+/** \internal \returns the bitwise not of \a a */
+template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
+pnot(const Packet& a) {
+  return bitwise_helper<Packet>::bitwise_not(a);
 }
 
 /** \internal \returns the bitwise and of \a a and not \a b */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
-pandnot(const Packet& a, const Packet& b) { return pand(a, pxor(ptrue(b), b)); }
+pandnot(const Packet& a, const Packet& b) { return pand(a, pnot(b)); }
+
+// In the general case, use bitwise select.
+template<typename Packet, typename EnableIf = void>
+struct pselect_impl {
+  static EIGEN_DEVICE_FUNC inline Packet run(const Packet& mask, const Packet& a, const Packet& b) {
+    return por(pand(a,mask),pandnot(b,mask));
+  }
+};
+
+// For scalars, use ternary select.
+template<typename Packet>
+struct pselect_impl<Packet, 
+    typename internal::enable_if<is_scalar<Packet>::value>::type > {
+  static EIGEN_DEVICE_FUNC inline Packet run(const Packet& mask, const Packet& a, const Packet& b) {
+    return numext::equal_strict(mask, Packet(0)) ? b : a;
+  }
+};
 
 /** \internal \returns \a or \b for each field in packet according to \mask */
 template<typename Packet> EIGEN_DEVICE_FUNC inline Packet
 pselect(const Packet& mask, const Packet& a, const Packet& b) {
-  return por(pand(a,mask),pandnot(b,mask));
-}
-
-template<> EIGEN_DEVICE_FUNC inline float pselect<float>(
-    const float& cond, const float& a, const float&b) {
-  return numext::equal_strict(cond,0.f) ? b : a;
-}
-
-template<> EIGEN_DEVICE_FUNC inline double pselect<double>(
-    const double& cond, const double& a, const double& b) {
-  return numext::equal_strict(cond,0.) ? b : a;
+  return pselect_impl<Packet>::run(mask, a, b);
 }
 
 template<> EIGEN_DEVICE_FUNC inline bool pselect<bool>(

Eigen/src/Core/util/XprHelper.h

@@ -184,19 +184,7 @@ template<typename T> struct functor_traits
 
 template<typename T> struct packet_traits;
 
-template<typename T> struct unpacket_traits
-{
-  typedef T type;
-  typedef T half;
-  enum
-  {
-    size = 1,
-    alignment = 1,
-    vectorizable = false,
-    masked_load_available=false,
-    masked_store_available=false
-  };
-};
+template<typename T> struct unpacket_traits;
 
 template<int Size, typename PacketType,
          bool Stop = Size==Dynamic || (Size%unpacket_traits<PacketType>::size)==0 || is_same<PacketType,typename unpacket_traits<PacketType>::half>::value>

test/AnnoyingScalar.h

@@ -126,7 +126,7 @@ template<>
 struct NumTraits<AnnoyingScalar> : NumTraits<float>
 {
   enum {
-    RequireInitialization = true
+    RequireInitialization = 1,
   };
   typedef AnnoyingScalar Real;
   typedef AnnoyingScalar Nested;
@@ -145,10 +145,6 @@ bool (isfinite)(const AnnoyingScalar& x) {
 }
 
 namespace internal {
-  template<> EIGEN_STRONG_INLINE AnnoyingScalar pcmp_eq(const AnnoyingScalar& a, const AnnoyingScalar& b)
-  { return AnnoyingScalar(pcmp_eq(*a.v, *b.v)); }
-  template<> EIGEN_STRONG_INLINE AnnoyingScalar pselect(const AnnoyingScalar& mask, const AnnoyingScalar& a, const AnnoyingScalar& b)
-  { return numext::equal_strict(*mask.v, 0.f) ? b : a; }
   template<> EIGEN_STRONG_INLINE double cast(const AnnoyingScalar& x) { return double(*x.v); }
   template<> EIGEN_STRONG_INLINE float  cast(const AnnoyingScalar& x) { return *x.v; }
 }