Fix test failure and add assert

Author: uditagarwal97

sycl/include/sycl/vector.hpp

@@ -789,8 +789,22 @@ template <typename Type, int NumElements> class vec {
     using bfloat16 = sycl::ext::oneapi::bfloat16;
     static_assert(std::is_integral_v<vec_data_t<convertT>> ||
                       detail::is_floating_point<convertT>::value ||
-                      std::is_same_v<convertT, bfloat16>,
+                      // Conversion to BF16 available only for float.
+                      (std::is_same_v<convertT, bfloat16> &&
+                       std::is_same_v<DataT, float>),
                   "Unsupported convertT");
+
+    // Currently, for BF16 <--> float conversion, we only support
+    // Round-to-even rounding mode.
+    constexpr bool isFloatToBF16Conv = std::is_same_v<convertT, bfloat16> &&
+        std::is_same_v<DataT, float>;
+    constexpr bool isBF16ToFloatConv = std::is_same_v<DataT, bfloat16> &&
+        std::is_same_v<convertT, float>;
+    if constexpr (isFloatToBF16Conv || isBF16ToFloatConv) {
+      static_assert(roundingMode == rounding_mode::automatic ||
+        roundingMode == rounding_mode::rte);
+    }
+
     using T = vec_data_t<DataT>;
     using R = vec_data_t<convertT>;
     using OpenCLT = detail::ConvertToOpenCLType_t<T>;
@@ -831,18 +845,18 @@ template <typename Type, int NumElements> class vec {
       // Otherwise, we fallback to per-element conversion:
       for (size_t I = 0; I < NumElements; ++I) {
         // For float -> bf16.
-        if constexpr (std::is_same_v<convertT, bfloat16>) {
+        if constexpr (isFloatToBF16Conv) {
           Result[I] = bfloat16((*this)[I]);
         } else
         // For bf16 -> float.
-        if constexpr (std::is_same_v<DataT, bfloat16>) {
+        if constexpr (isBF16ToFloatConv) {
           Result[I] = (float)((*this)[I]);
         }
         else {
           Result.setValue(
               I, vec_data<convertT>::get(
                      detail::convertImpl<T, R, roundingMode, 1, OpenCLT, OpenCLR>(
-                         vec_data<T>::get(getValue(I)))));
+                         vec_data<DataT>::get(getValue(I)))));
         }
       }
     }

sycl/include/sycl/vector_preview.hpp

@@ -419,10 +419,24 @@ class vec : public detail::vec_arith<DataT, NumElements> {
 
     using T = ConvertBoolAndByteT<DataT>;
     using R = ConvertBoolAndByteT<convertT>;
+    using bfloat16 = sycl::ext::oneapi::bfloat16;
     static_assert(std::is_integral_v<R> || detail::is_floating_point<R>::value ||
-                      std::is_same_v<R, sycl::ext::oneapi::bfloat16>,
+                      std::is_same_v<R, bfloat16>,
                   "Unsupported convertT");
 
+    {
+      // Currently, for BF16 <--> float conversion, we only support
+      // Round-to-even rounding mode.
+      constexpr bool isFloatToBF16Conv = std::is_same_v<convertT, bfloat16> &&
+          std::is_same_v<DataT, float>;
+      constexpr bool isBF16ToFloatConv = std::is_same_v<DataT, bfloat16> &&
+          std::is_same_v<convertT, float>;
+      if constexpr (isFloatToBF16Conv || isBF16ToFloatConv) {
+        static_assert(roundingMode == rounding_mode::automatic ||
+          roundingMode == rounding_mode::rte);
+      }
+    }
+
     using OpenCLT = detail::ConvertToOpenCLType_t<T>;
     using OpenCLR = detail::ConvertToOpenCLType_t<R>;
     vec<convertT, NumElements> Result;
@@ -482,7 +496,7 @@ class vec : public detail::vec_arith<DataT, NumElements> {
                   getValue(I));
 #ifdef __SYCL_DEVICE_ONLY__
           // On device, we interpret BF16 as uint16.
-          if constexpr (std::is_same_v<convertT, sycl::ext::oneapi::bfloat16>)
+          if constexpr (std::is_same_v<convertT, bfloat16>)
             Result[I] = sycl::bit_cast<convertT>(val);
           else
 #endif