refine conditional compilation and remove `numel_`

paddle/framework/tensor.h

@@ -27,7 +27,7 @@ namespace framework {
 
 class Tensor {
  public:
-  Tensor() : numel_(0), offset_(0) {}
+  Tensor() : offset_(0) {}
 
   template <typename T>
   const T* data() const {
@@ -44,30 +44,26 @@ class Tensor {
 
   template <typename T>
   T* mutable_data(platform::Place place) {
-    PADDLE_ENFORCE(numel_ > 0,
-                   "Tensor::numel_ must be larger than zero to call "
+    PADDLE_ENFORCE(product(dims_) > 0,
+                   "Tensor's numel must be larger than zero to call "
                    "Tensor::mutable_data. Call Tensor::set_dim first.");
     if (holder_ == nullptr ||
         !(holder_->place() ==
           place) /* some versions of boost::variant don't have operator!= */
-        || holder_->size() < numel_ * sizeof(T) + offset_) {
+        || holder_->size() < product(dims_) * sizeof(T) + offset_) {
+      if (platform::is_cpu_place(place)) {
+        holder_.reset(new PlaceholderImpl<T, platform::CPUPlace>(
+            boost::get<platform::CPUPlace>(place), product(dims_) * sizeof(T)));
+      } else if (platform::is_gpu_place(place)) {
 #ifdef __CUDACC__
-      switch (place.which()) {
-        case 0:
         holder_.reset(new PlaceholderImpl<T, platform::GPUPlace>(
-              boost::get<platform::GPUPlace>(place), numel_ * sizeof(T)));
-          break;
-
-        case 1:
-          holder_.reset(new PlaceholderImpl<T, platform::CPUPlace>(
-              boost::get<platform::CPUPlace>(place), numel_ * sizeof(T)));
-          break;
-      }
+            boost::get<platform::GPUPlace>(place), product(dims_) * sizeof(T)));
 #else
-      holder_.reset(new PlaceholderImpl<T, platform::CPUPlace>(
-          boost::get<platform::CPUPlace>(place), numel_ * sizeof(T)));
+        PADDLE_ENFORCE(true, "'GPUPlace' is not supported in CPU only device.");
 #endif
-
+      } else {
+        PADDLE_ENFORCE(true, "Unknown 'place'.");
+      }
       offset_ = 0;
     }
     return reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(holder_->ptr()) +
@@ -88,7 +84,7 @@ class Tensor {
                        platform::is_cpu_place(dst_place),
                    "Tensor::CopyFrom only support CPU now.");
     src.CheckDims<T>();
-    size_t size = src.numel_ * sizeof(T);
+    size_t size = product(src.dims_) * sizeof(T);
     set_dims(src.dims());
     const void* src_ptr = static_cast<const void*>(src.data<T>());
     void* dst_ptr = static_cast<void*>(mutable_data<T>(dst_place));
@@ -122,7 +118,6 @@ class Tensor {
       return;
     }
     dims_ = dims;
-    numel_ = product(dims_);
   }
 
   DDim dims() const { return dims_; }
@@ -170,16 +165,15 @@ class Tensor {
   inline void CheckDims() const {
     PADDLE_ENFORCE(holder_ != nullptr,
                    "Tenosr holds no memory. Call Tensor::mutable_data first.");
-    PADDLE_ENFORCE(holder_->size() >= numel_ * sizeof(T) + offset_,
+    PADDLE_ENFORCE(holder_->size() >= product(dims_) * sizeof(T) + offset_,
                    "Tensor's dims_ is out of bound. Call Tensor::mutable_data "
                    "first to re-allocate memory.");
   }
 
   std::shared_ptr<Placeholder> holder_;  // holds the memory block if allocated.
   DDim dims_;
-  size_t numel_;   // cache of `product(dims_)`
   size_t offset_;  // marks the begin of tensor data area.
-};                 // namespace framework
+};
 
 }  // namespace framework
 }  // namespace paddle