chore: import upstream snapshot with attribution

paddle/phi/kernels/reduce_variance_kernel.cc

@@ -0,0 +1,45 @@
+// Copyright (c) 2025 PaddlePaddle Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "paddle/phi/kernels/reduce_variance_kernel.h"
+#include "paddle/phi/kernels/elementwise_multiply_kernel.h"
+#include "paddle/phi/kernels/elementwise_subtract_kernel.h"
+#include "paddle/phi/kernels/reduce_mean_kernel.h"
+
+#include "paddle/phi/backends/all_context.h"
+#include "paddle/phi/core/kernel_registry.h"
+
+namespace phi {
+template <typename T, typename Context>
+void VarianceKernel(const Context& dev_ctx,
+                    const DenseTensor& x,
+                    const std::vector<int64_t>& dims,
+                    bool keep_dim,
+                    DenseTensor* out) {
+  DenseTensor temp_mean = Mean<T, Context>(dev_ctx, x, dims, true);
+  DenseTensor temp_differences = Subtract<T, Context>(dev_ctx, x, temp_mean);
+  DenseTensor temp_pow =
+      Multiply<T, Context>(dev_ctx, temp_differences, temp_differences);
+
+  MeanKernel<T, Context>(dev_ctx, temp_pow, dims, keep_dim, out);
+}
+}  // namespace phi
+
+PD_REGISTER_KERNEL(
+    variance, CPU, ALL_LAYOUT, phi::VarianceKernel, float, double) {}
+
+#if defined(PADDLE_WITH_CUDA) || defined(PADDLE_WITH_HIP)
+PD_REGISTER_KERNEL(
+    variance, GPU, ALL_LAYOUT, phi::VarianceKernel, float, double) {}
+#endif