[NFC][SYCL] Minor refactoring in sycl::vec

sycl/include/sycl/detail/named_swizzles_mixin.hpp

@@ -18,6 +18,9 @@ namespace sycl {
 inline namespace _V1 {
 namespace detail {
 
+// Will be defined in another header.
+template <typename T> struct from_incomplete;
+
 #ifndef SYCL_SIMPLE_SWIZZLES
 #define __SYCL_SWIZZLE_MIXIN_SIMPLE_SWIZZLES
 #else
@@ -785,7 +788,8 @@ namespace detail {
     return (*static_cast<const Self_ *>(this))[INDEX];                         \
   }
 
-template <typename Self, int NumElements> struct NamedSwizzlesMixinConst {
+template <typename Self, int NumElements = from_incomplete<Self>::size()>
+struct NamedSwizzlesMixinConst {
 #define __SYCL_SWIZZLE_MIXIN_METHOD(COND, NAME, ...)                           \
   __SYCL_SWIZZLE_MIXIN_METHOD_CONST(COND, NAME, __VA_ARGS__)
 
@@ -798,7 +802,8 @@ template <typename Self, int NumElements> struct NamedSwizzlesMixinConst {
 #undef __SYCL_SWIZZLE_MIXIN_METHOD
 };
 
-template <typename Self, int NumElements> struct NamedSwizzlesMixinBoth {
+template <typename Self, int NumElements = from_incomplete<Self>::size()>
+struct NamedSwizzlesMixinBoth {
 #define __SYCL_SWIZZLE_MIXIN_METHOD(COND, NAME, ...)                           \
   __SYCL_SWIZZLE_MIXIN_METHOD_NON_CONST(COND, NAME, __VA_ARGS__)               \
   __SYCL_SWIZZLE_MIXIN_METHOD_CONST(COND, NAME, __VA_ARGS__)

sycl/include/sycl/detail/vector_arith.hpp

@@ -21,6 +21,19 @@ template <typename DataT, int NumElem> class __SYCL_EBO vec;
 
 namespace detail {
 
+template <typename T> struct from_incomplete;
+template <typename T>
+struct from_incomplete<const T> : public from_incomplete<T> {};
+
+template <typename DataT, int NumElements>
+struct from_incomplete<vec<DataT, NumElements>> {
+  using element_type = DataT;
+  static constexpr size_t size() { return NumElements; }
+};
+
+template <bool Cond, typename Mixin> struct ApplyIf {};
+template <typename Mixin> struct ApplyIf<true, Mixin> : Mixin {};
+
 // We use std::plus<void> and similar to "map" template parameter to an
 // overloaded operator. These three below are missing from `<functional>`.
 struct ShiftLeft {

sycl/include/sycl/vector.hpp

@@ -113,12 +113,11 @@ template <typename T> class GetOp {
 //
 // must go throw `v.x()` returning a swizzle, then its `operator==` returning
 // vec<int, 1> and we want that code to compile.
-template <typename Vec, typename T, int N, typename = void>
-struct ScalarConversionOperatorMixIn {};
+template <typename Self> class ScalarConversionOperatorMixIn {
+  using T = typename from_incomplete<Self>::element_type;
 
-template <typename Vec, typename T, int N>
-struct ScalarConversionOperatorMixIn<Vec, T, N, std::enable_if_t<N == 1>> {
-  operator T() const { return (*static_cast<const Vec *>(this))[0]; }
+public:
+  operator T() const { return (*static_cast<const Self *>(this))[0]; }
 };
 
 template <typename T>
@@ -134,10 +133,10 @@ inline constexpr bool is_fundamental_or_half_or_bfloat16 =
 template <typename DataT, int NumElements>
 class __SYCL_EBO vec
     : public detail::vec_arith<DataT, NumElements>,
-      public detail::ScalarConversionOperatorMixIn<vec<DataT, NumElements>,
-                                                   DataT, NumElements>,
-      public detail::NamedSwizzlesMixinBoth<vec<DataT, NumElements>,
-                                            NumElements> {
+      public detail::ApplyIf<
+          NumElements == 1,
+          detail::ScalarConversionOperatorMixIn<vec<DataT, NumElements>>>,
+      public detail::NamedSwizzlesMixinBoth<vec<DataT, NumElements>> {
   static_assert(std::is_same_v<DataT, std::remove_cv_t<DataT>>,
                 "DataT must be cv-unqualified");
 
@@ -177,6 +176,24 @@ class __SYCL_EBO vec
                                   element_type_for_vector_t __attribute__((
                                       ext_vector_type(NumElements)))>;
 
+  // Make it a template to avoid ambiguity with `vec(const DataT &)` when
+  // `vector_t` is the same as `DataT`. Not that the other ctor isn't a template
+  // so we don't even need a smart `enable_if` condition here, the mere fact of
+  // this being a template makes the other ctor preferred.
+  template <
+      typename vector_t_ = vector_t,
+      typename = typename std::enable_if_t<std::is_same_v<vector_t_, vector_t>>>
+  constexpr vec(vector_t_ openclVector) {
+    m_Data = sycl::bit_cast<DataType>(openclVector);
+  }
+
+  /* @SYCL2020
+   * Available only when: compiled for the device.
+   * Converts this SYCL vec instance to the underlying backend-native vector
+   * type defined by vector_t.
+   */
+  operator vector_t() const { return sycl::bit_cast<vector_t>(m_Data); }
+
 private:
 #endif // __SYCL_DEVICE_ONLY__
 
@@ -299,26 +316,6 @@ class __SYCL_EBO vec
     return *this;
   }
 
-#ifdef __SYCL_DEVICE_ONLY__
-  // Make it a template to avoid ambiguity with `vec(const DataT &)` when
-  // `vector_t` is the same as `DataT`. Not that the other ctor isn't a template
-  // so we don't even need a smart `enable_if` condition here, the mere fact of
-  // this being a template makes the other ctor preferred.
-  template <
-      typename vector_t_ = vector_t,
-      typename = typename std::enable_if_t<std::is_same_v<vector_t_, vector_t>>>
-  constexpr vec(vector_t_ openclVector) {
-    m_Data = sycl::bit_cast<DataType>(openclVector);
-  }
-
-  /* @SYCL2020
-   * Available only when: compiled for the device.
-   * Converts this SYCL vec instance to the underlying backend-native vector
-   * type defined by vector_t.
-   */
-  operator vector_t() const { return sycl::bit_cast<vector_t>(m_Data); }
-#endif // __SYCL_DEVICE_ONLY__
-
   __SYCL2020_DEPRECATED("get_count() is deprecated, please use size() instead")
   static constexpr size_t get_count() { return size(); }
   static constexpr size_t size() noexcept { return NumElements; }