[Arm] Update Fc arm kernel implementation to reduce memory usage (#3949)

lite/kernels/arm/fc_compute.cc

@@ -88,7 +88,7 @@ void FcCompute<PRECISION(kFloat), PRECISION(kFloat)>::Run() {
 
   auto i_data = param.input->data<float>();
   auto o_data = param.output->mutable_data<float>();
-  auto w_data = flag_gemm_ ? param.w->data<float>() : weights_.data<float>();
+  auto w_data = param.w->data<float>();
   const float* b_data = param.bias ? param.bias->data<float>() : nullptr;
   if (flag_trans_bias_) {
     b_data = bias_.data<float>();
@@ -149,8 +149,7 @@ void FcCompute<PRECISION(kInt8), PRECISION(kFloat)>::Run() {
 
   auto i_data = param.input->data<int8_t>();
   auto o_data = param.output->mutable_data<float>();
-  auto w_data =
-      flag_trans_weights_ ? weights_.data<int8_t>() : param.w->data<int8_t>();
+  auto w_data = param.w->data<int8_t>();
   const float* b_data = param.bias ? param.bias->data<float>() : nullptr;
   if (flag_trans_bias_) {
     b_data = bias_.data<float>();
@@ -208,8 +207,7 @@ void FcCompute<PRECISION(kInt8), PRECISION(kInt8)>::Run() {
 
   auto i_data = param.input->data<int8_t>();
   auto o_data = param.output->mutable_data<int8_t>();
-  auto w_data =
-      flag_trans_weights_ ? weights_.data<int8_t>() : param.w->data<int8_t>();
+  auto w_data = param.w->data<int8_t>();
   const float* b_data = param.bias ? param.bias->data<float>() : nullptr;
   if (flag_trans_bias_) {
     b_data = bias_.data<float>();

lite/kernels/arm/fc_compute.h

@@ -104,9 +104,11 @@ class FcCompute : public KernelLite<TARGET(kARM), PType> {
     CHECK_EQ(k_, static_cast<int>(w_dims[0]));
     flag_gemm_ = check_fc_use_gemm<PType, OutType>(
         m_, param.weight_scale, param.bias != nullptr);
-    if (!flag_trans_weights_ && !flag_gemm_) {
-      flag_trans_weights_ = true;
-      fc_trans_weights<PType>(*param.w, &weights_);
+    if (flag_trans_weights_ == flag_gemm_) {
+      flag_trans_weights_ = !flag_trans_weights_;
+      Tensor tmp_tensor;
+      fc_trans_weights<PType>(*param.w, &tmp_tensor);
+      param.w->CopyDataFrom(tmp_tensor);
     }
   }
 
@@ -117,7 +119,6 @@ class FcCompute : public KernelLite<TARGET(kARM), PType> {
 
  private:
   DDim last_shape_;
-  Tensor weights_;
   Tensor bias_;
   bool flag_trans_weights_{false};
   bool flag_trans_bias_{false};