Added unpaddedSize_ to Tensor (#2970)

Summary:
This PR adds a new field to Tensor: unpaddedSize_.
Since we have a static batch size we copy the entire tensor to the device regardless of number of inputs. This would allow a DeviceManager to only copy the inputs if it supports it.
This means adding additional metaData to Tensor, this seemed cleaner than passing side channel data.

Documentation: NA
Pull Request resolved: #2970

Differential Revision: D15577757

Pulled By: gcatron

fbshipit-source-id: 105bad588c13cd6746a63e14594c0ba57c8fb974

Author: gcatron

include/glow/Base/Tensor.h

@@ -69,6 +69,11 @@ class Tensor final {
   /// The TensorPool that is managing this Tensor (if any).
   TensorPool *tensorPool_{nullptr};
 
+  /// Size in bytes of the unpadded region memory. This is useful  communicating
+  /// the actual size of the data, this allows for copying only inputs and not
+  /// padding to the device.
+  size_t unpaddedSize_{0};
+
   template <class ElemTy> friend class Handle;
 
   /// \returns a pointer to the tensor data buffer.
@@ -78,6 +83,10 @@ class Tensor final {
   /// \returns true if it is an unowned tensor.
   bool isUnowned() const { return isUnowned_; }
 
+  /// \returns the size of the unpadded memory region. If unpaddedSize_ is not
+  /// set return the size of the entire payload.
+  size_t getUnpaddedSizeInBytes() const;
+
   /// \returns the type of the tensor.
   const Type &getType() const { return type_; }
 
@@ -206,9 +215,11 @@ class Tensor final {
 
   /// Construct an unowned tensor provided an existing payload buffer.
   /// This constructor can be used when there is a need to work with
-  /// "externally" managed payload buffers using Tensor APIs.
-  Tensor(void *data, TypeRef ty)
-      : data_(reinterpret_cast<char *>(data)), type_(*ty), isUnowned_{false} {
+  /// "externally" managed payload buffers using Tensor APIs. Additionally \p
+  /// unpaddedSize can be set to indicate actual size of the inputs.
+  Tensor(void *data, TypeRef ty, size_t unpaddedSize = 0)
+      : data_(reinterpret_cast<char *>(data)),
+        type_(*ty), isUnowned_{false}, unpaddedSize_{unpaddedSize} {
     // Mark as unowned.
     isUnowned_ = true;
   }

lib/Base/Tensor.cpp

@@ -515,3 +515,11 @@ void Tensor::convertToType(ElemKind newTy) {
   }
   *this = std::move(tmp);
 }
+
+size_t Tensor::getUnpaddedSizeInBytes() const {
+  if (unpaddedSize_) {
+    return unpaddedSize_;
+  } else {
+    return type_.getSizeInBytes();
+  }
+}