[backport] Allow unaligned pointer if the array is empty. (dmlc#10418) (dmlc#10424)

Co-authored-by: Philip Hyunsu Cho <[email protected]>

Author: trivialfis

src/data/array_interface.h

@@ -6,28 +6,25 @@
 #ifndef XGBOOST_DATA_ARRAY_INTERFACE_H_
 #define XGBOOST_DATA_ARRAY_INTERFACE_H_
 
-#include <algorithm>
-#include <cstddef>  // for size_t
-#include <cstdint>
-#include <limits>  // for numeric_limits
-#include <map>
-#include <string>
+#include <algorithm>    // for all_of, transform, fill
+#include <cstddef>      // for size_t
+#include <cstdint>      // for int32_t, int64_t, ...
+#include <limits>       // for numeric_limits
+#include <map>          // for map
+#include <string>       // for string
 #include <type_traits>  // for alignment_of, remove_pointer_t, invoke_result_t
-#include <utility>
-#include <vector>
+#include <vector>       // for vector
 
-#include "../common/bitfield.h"  // for RBitField8
-#include "../common/common.h"
+#include "../common/bitfield.h"   // for RBitField8
 #include "../common/error_msg.h"  // for NoF128
-#include "xgboost/base.h"
-#include "xgboost/data.h"
-#include "xgboost/json.h"
-#include "xgboost/linalg.h"
-#include "xgboost/logging.h"
-#include "xgboost/span.h"
+#include "xgboost/json.h"         // for Json
+#include "xgboost/linalg.h"       // for CalcStride, TensorView
+#include "xgboost/logging.h"      // for CHECK
+#include "xgboost/span.h"         // for Span
+#include "xgboost/string_view.h"  // for StringView
 
 #if defined(XGBOOST_USE_CUDA)
-#include "cuda_fp16.h"
+#include "cuda_fp16.h"  // for __half
 #endif
 
 namespace xgboost {
@@ -410,7 +407,7 @@ class ArrayInterface {
     auto typestr = get<String const>(array.at("typestr"));
     this->AssignType(StringView{typestr});
     ArrayInterfaceHandler::ExtractShape(array, shape);
-    size_t itemsize = typestr[2] - '0';
+    std::size_t itemsize = typestr[2] - '0';
     is_contiguous = ArrayInterfaceHandler::ExtractStride(array, itemsize, shape, strides);
     n = linalg::detail::CalcSize(shape);
 
@@ -419,7 +416,9 @@ class ArrayInterface {
 
     auto alignment = this->ElementAlignment();
     auto ptr = reinterpret_cast<uintptr_t>(this->data);
-    CHECK_EQ(ptr % alignment, 0) << "Input pointer misalignment.";
+    if (!std::all_of(this->shape, this->shape + D, [](auto v) { return v == 0; })) {
+      CHECK_EQ(ptr % alignment, 0) << "Input pointer misalignment.";
+    }
 
     if (allow_mask) {
       common::Span<RBitField8::value_type> s_mask;