!13369 fix cpu UnsortedSegmentSum

From: @zhao_ting_v
Reviewed-by: @wuxuejian
Signed-off-by: @wuxuejian

mindspore/ccsrc/backend/kernel_compiler/cpu/unsorted_segment_sum_cpu_kernel.cc

@@ -16,7 +16,6 @@
 
 #include "backend/kernel_compiler/cpu/unsorted_segment_sum_cpu_kernel.h"
 #include <string>
-#include <cmath>
 #include "runtime/device/cpu/cpu_device_address.h"
 #include "common/thread_pool.h"
 
@@ -79,18 +78,7 @@ bool UnsortedSegmentSumCPUKernel::LaunchKernel(const std::vector<AddressPtr> &in
     MS_LOG(ERROR) << "Output buff memset fail. ret:" << ret;
     return false;
   }
-  size_t thread_num = common::ThreadPool::GetInstance().GetSyncRunThreadNum();
-  if (unit_num_ < thread_num) {
-    thread_num = unit_num_;
-  }
-  std::vector<common::Task> tasks;
-  tasks.reserve(thread_num);
-  auto task = [&](size_t start, size_t end) {
-    for (size_t c = 0; c < ceil(static_cast<double>(unit_num_) / thread_num); ++c) {
-      if (c * thread_num + start >= unit_num_) {
-        continue;
-      }
-      size_t i = c * thread_num + start;
+  for (size_t i = 0; i < unit_num_; ++i) {
     size_t j = i / input_dim1_;
     size_t k = i % input_dim1_;
 
@@ -101,15 +89,6 @@ bool UnsortedSegmentSumCPUKernel::LaunchKernel(const std::vector<AddressPtr> &in
     size_t output_index = index * output_dim1_ + k;
     output_addr[output_index] += input_addr[i];
   }
-  };
-  for (size_t t = 0; t < thread_num; ++t) {
-    auto block = [&, t]() {
-      task(t, t + 1);
-      return common::SUCCESS;
-    };
-    tasks.emplace_back(block);
-  }
-  common::ThreadPool::GetInstance().SyncRun(tasks);
   return true;
 }
 }  // namespace kernel