[Auto Parallel] remove redundant reshard when mesh==1

paddle/phi/core/distributed/auto_parallel/reshard/p_to_r_reshard_function.cc

@@ -50,6 +50,11 @@ void PToRReshardFunction::Eval(DeviceContext* dev_ctx,
   const auto& in_dist_attr = in.dist_attr();
   const auto& in_process_mesh = in_dist_attr.process_mesh();
   const auto& in_process_ids = in_process_mesh.process_ids();
+  if (in_process_ids.size() == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
   const auto& in_partial_status = in_dist_attr.partial_status();
   auto in_reduce_type = in_partial_status.at(0);
   bool reduce_mean = false;

paddle/phi/core/distributed/auto_parallel/reshard/p_to_s_reshard_function.cc

@@ -121,6 +121,11 @@ void PToSReshardFunction::Eval(DeviceContext* dev_ctx,
   int out_split_axis =
       GetSplitAxisWithDimsMapping(out_dist_attr.dims_mapping()).begin()->first;
   int64_t num_of_process = in_process_mesh.size();
+  if (num_of_process == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
   int64_t num_of_padding = in.dims()[out_split_axis] % num_of_process;
   bool is_balanced_split = (num_of_padding == 0);
 

paddle/phi/core/distributed/auto_parallel/reshard/r_to_p_reshard_function.cc

@@ -48,6 +48,12 @@ void RToPReshardFunction::Eval(phi::DeviceContext* dev_ctx,
                                const TensorDistAttr& out_dist_attr,
                                DistTensor* out) {
   VLOG(3) << "Call " << Name();
+  const auto& in_process_ids = in.dist_attr().process_mesh().process_ids();
+  if (in_process_ids.size() == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
   const auto& out_process_mesh = out_dist_attr.process_mesh();
   int64_t local_rank = GetCurRankCoordInMesh(out_process_mesh)[0];
   const auto& in_reduce_type = out_dist_attr.partial_status().at(0);

paddle/phi/core/distributed/auto_parallel/reshard/r_to_s_reshard_function.cc

@@ -59,6 +59,11 @@ void RToSReshardFunction::Eval(phi::DeviceContext* dev_ctx,
   int64_t mesh_axis = split_axis_to_mesh_axis.begin()->second;
 
   int64_t num_of_process = out_process_mesh.shape()[mesh_axis];
+  if (num_of_process == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
   VLOG(3) << "RToSReshard: Tensor will be split on axis " << split_axis
           << ". Split will use axis " << mesh_axis << " of process_mesh."
           << " There will have " << num_of_process

paddle/phi/core/distributed/auto_parallel/reshard/s_to_r_reshard_function.cc

@@ -109,6 +109,11 @@ void SToRReshardFunction::Eval(DeviceContext* dev_ctx,
   const auto& in_dims_mapping = in_dist_attr.dims_mapping();
   const auto& in_process_mesh = in_dist_attr.process_mesh();
   const auto& in_process_ids = in_process_mesh.process_ids();
+  if (in_process_ids.size() == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
 
   int split_axis = GetSplitAxisWithDimsMapping(in_dims_mapping).begin()->first;
   int64_t num_of_process = in_process_mesh.size();

paddle/phi/core/distributed/auto_parallel/reshard/s_to_s_reshard_function.cc

@@ -54,6 +54,11 @@ void SToSReshardFunction::Eval(phi::DeviceContext* dev_ctx,
   VLOG(3) << "Call " << Name();
   const auto& in_process_mesh = in.dist_attr().process_mesh();
   const auto& in_process_ids = in_process_mesh.process_ids();
+  if (in_process_ids.size() == 1) {
+    SetValue(out, in.value());
+    SetDistProps(out, in.dims(), out_dist_attr);
+    return;
+  }
   auto dtype = in.dtype();
   const auto& logical_ddim = in.dims();
   int64_t nranks = static_cast<int64_t>(in_process_ids.size());