Optimize array interface input.

src/common/error_msg.h

@@ -24,5 +24,9 @@ constexpr StringView LabelScoreSize() {
 constexpr StringView InfInData() {
   return "Input data contains `inf` or a value too large, while `missing` is not set to `inf`";
 }
+
+constexpr StringView NoF128() {
+  return "128-bit floating point is not supported on current platform.";
+}
 }  // namespace xgboost::error
 #endif  // XGBOOST_COMMON_ERROR_MSG_H_

src/data/array_interface.h

@@ -7,8 +7,9 @@
 #define XGBOOST_DATA_ARRAY_INTERFACE_H_
 
 #include <algorithm>
-#include <cstddef>  // std::size_t
+#include <cstddef>  // for size_t
 #include <cstdint>
+#include <limits>  // for numeric_limits
 #include <map>
 #include <string>
 #include <type_traits>  // std::alignment_of,std::remove_pointer_t
@@ -17,6 +18,7 @@
 
 #include "../common/bitfield.h"
 #include "../common/common.h"
+#include "../common/error_msg.h"  // for NoF128
 #include "xgboost/base.h"
 #include "xgboost/data.h"
 #include "xgboost/json.h"
@@ -454,9 +456,8 @@ class ArrayInterface {
   void AssignType(StringView typestr) {
     using T = ArrayInterfaceHandler::Type;
     if (typestr.size() == 4 && typestr[1] == 'f' && typestr[2] == '1' && typestr[3] == '6') {
+      CHECK(sizeof(long double) == 16) << error::NoF128();
       type = T::kF16;
-      CHECK(sizeof(long double) == 16)
-          << "128-bit floating point is not supported on current platform.";
     } else if (typestr[1] == 'f' && typestr[2] == '2') {
 #if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 600
       type = T::kF2;
@@ -572,19 +573,90 @@ class ArrayInterface {
   // Used only by columnar format.
   RBitField8 valid;
   // Array stride
-  size_t strides[D]{0};
+  std::size_t strides[D]{0};
   // Array shape
-  size_t shape[D]{0};
+  std::size_t shape[D]{0};
   // Type earsed pointer referencing the data.
   void const *data{nullptr};
   // Total number of items
-  size_t n{0};
+  std::size_t n{0};
   // Whether the memory is c-contiguous
   bool is_contiguous{false};
   // RTTI, initialized to the f16 to avoid masking potential bugs in initialization.
   ArrayInterfaceHandler::Type type{ArrayInterfaceHandler::kF16};
 };
 
+template <std::int32_t D, typename Fn>
+void DispatchDType(ArrayInterface<D> const array, std::int32_t device, Fn fn) {
+  // Only used for cuDF at the moment.
+  CHECK_EQ(array.valid.Size(), 0);
+  auto dispatch = [&](auto t) {
+    using T = std::remove_const_t<decltype(t)> const;
+    // Set the data size to max as we don't know the original size of a sliced array:
+    //
+    // Slicing an array A with shape (4, 2, 3) and stride (6, 3, 1) by [:, 1, :] results
+    // in an array B with shape (4, 3) and strides (6, 1). We can't calculate the original
+    // size 24 based on the slice.
+    fn(linalg::TensorView<T, D>{common::Span<T const>{static_cast<T *>(array.data),
+                                                      std::numeric_limits<std::size_t>::max()},
+                                array.shape, array.strides, device});
+  };
+  switch (array.type) {
+    case ArrayInterfaceHandler::kF2: {
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 600
+      dispatch(__half{});
+#endif
+      break;
+    }
+    case ArrayInterfaceHandler::kF4: {
+      dispatch(float{});
+      break;
+    }
+    case ArrayInterfaceHandler::kF8: {
+      dispatch(double{});
+      break;
+    }
+    case ArrayInterfaceHandler::kF16: {
+      using T = long double;
+      CHECK(sizeof(long double) == 16) << error::NoF128();
+      dispatch(T{});
+      break;
+    }
+    case ArrayInterfaceHandler::kI1: {
+      dispatch(std::int8_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kI2: {
+      dispatch(std::int16_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kI4: {
+      dispatch(std::int32_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kI8: {
+      dispatch(std::int64_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kU1: {
+      dispatch(std::uint8_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kU2: {
+      dispatch(std::uint16_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kU4: {
+      dispatch(std::uint32_t{});
+      break;
+    }
+    case ArrayInterfaceHandler::kU8: {
+      dispatch(std::uint64_t{});
+      break;
+    }
+  }
+}
+
 /**
  * \brief Helper for type casting.
  */

src/data/data.cc

@@ -427,10 +427,13 @@ void CopyTensorInfoImpl(Context const& ctx, Json arr_interface, linalg::Tensor<T
     return;
   }
   p_out->Reshape(array.shape);
-  auto t = p_out->View(Context::kCpuId);
-  CHECK(t.CContiguous());
-  linalg::ElementWiseTransformHost(t, ctx.Threads(), [&](auto i, auto) {
-    return linalg::detail::Apply(TypedIndex<T, D>{array}, linalg::UnravelIndex<D>(i, t.Shape()));
+  auto t_out = p_out->View(Context::kCpuId);
+  CHECK(t_out.CContiguous());
+  auto const shape = t_out.Shape();
+  DispatchDType(array, Context::kCpuId, [&](auto&& in) {
+    linalg::ElementWiseTransformHost(t_out, ctx.Threads(), [&](auto i, auto) {
+      return std::apply(in, linalg::UnravelIndex<D>(i, shape));
+    });
   });
 }
 }  // namespace