Refactor softmax_cudnn kernel impl for code reuse. (#35350)

paddle/fluid/operators/softmax_impl.cuh

-/* Copyright (c) 2021 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. */
-
-#pragma once
-
-#include "paddle/fluid/platform/cuda_device_function.h"
-
-namespace paddle {
-namespace operators {
-
-template <typename T, int BatchSize, int WarpSize>
-__device__ __forceinline__ void WarpReduceSum(T* sum) {
-#pragma unroll
-  for (int offset = WarpSize / 2; offset > 0; offset /= 2) {
-#pragma unroll
-    for (int i = 0; i < BatchSize; ++i) {
-      T sum_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
-      sum[i] = sum[i] + sum_val;
-    }
-  }
-}
-
-template <typename T, int BatchSize, int WarpSize>
-__device__ __forceinline__ void WarpReduceMax(T* sum) {
-#pragma unroll
-  for (int offset = WarpSize / 2; offset > 0; offset /= 2) {
-#pragma unroll
-    for (int i = 0; i < BatchSize; ++i) {
-      T max_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
-      sum[i] = max(sum[i], max_val);
-    }
-  }
-}
-
-}  // namespace operators
-}  // namespace paddle
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