replace index_select_grad_init with SetConstant

Author: FlyingQianMM

paddle/phi/kernels/gpu/index_select_grad_kernel.cu

@@ -19,6 +19,7 @@
 #include "paddle/phi/backends/gpu/gpu_info.h"
 #include "paddle/phi/core/kernel_registry.h"
 #include "paddle/phi/core/utils/data_type.h"
+#include "paddle/phi/kernels/funcs/math_function.h"
 
 DECLARE_bool(cudnn_deterministic);
 
@@ -45,11 +46,6 @@ __global__ void index_select_grad_cuda_kernel(const T* output_grad,
   }
 }
 
-template <typename T>
-__global__ void index_select_grad_init(T* input_grad, int64_t N) {
-  CUDA_KERNEL_LOOP_TYPE(idx, N, int64_t) { input_grad[idx] = 0.0; }
-}
-
 template <typename T, typename Context>
 void IndexSelectGradKernel(const Context& ctx,
                            const DenseTensor& x,
@@ -93,8 +89,8 @@ void IndexSelectGradKernel(const Context& ctx,
   dim3 grid_dim = dim3((numel + block_dim - 1) / block_dim);
   paddle::platform::LimitGridDim(ctx, &grid_dim);
 
-  index_select_grad_init<T><<<grid_dim, block_dim, 0, stream>>>(in_grad_data,
-                                                                numel);
+  phi::funcs::SetConstant<phi::GPUContext, T> index_select_grad_init;
+  index_select_grad_init(ctx, x_grad, static_cast<T>(0));
 
   if (FLAGS_cudnn_deterministic) {
     VLOG(2) << "Run grad kernel of index_select with single thread.";