Do not use std::vector in getResourceRequirements

unsupported/Eigen/CXX11/src/Tensor/TensorBlockV2.h

@@ -57,6 +57,60 @@ EIGEN_STRONG_INLINE DSizes<std::ptrdiff_t, sizeof...(Indices)> strides(
   return strides<Layout>(DSizes<std::ptrdiff_t, sizeof...(Indices)>(sizes));
 }
 
+// -------------------------------------------------------------------------- //
+
+// Tensor block shape type defines what are the shape preference for the blocks
+// extracted from the larger tensor.
+//
+// Example: blocks of 100 elements from the large 100x100 tensor:
+// - tensor: 100x100
+// - target_block_size: 100
+//
+// TensorBlockShapeType:
+//  - kUniformAllDims: 100 blocks of size 10x10
+//  - kSkewedInnerDims: 100 blocks of size 100x1 (or 1x100 depending on a column
+//                      or row major layout)
+enum class TensorBlockV2ShapeType { kUniformAllDims, kSkewedInnerDims };
+
+struct TensorBlockV2ResourceRequirements {
+  TensorBlockV2ShapeType shape_type;
+  size_t size;
+
+  TensorBlockShapeType shapeV1() const {
+    return shape_type == TensorBlockV2ShapeType::kUniformAllDims
+               ? internal::kUniformAllDims
+               : internal::kSkewedInnerDims;
+  }
+
+  static TensorBlockV2ResourceRequirements
+  merge(const TensorBlockV2ResourceRequirements &lhs,
+        const TensorBlockV2ResourceRequirements &rhs) {
+    return {merge(lhs.shape_type, rhs.shape_type), merge(rhs.size, lhs.size)};
+  }
+
+  // This is a resource requirement that should be returned from expressions
+  // that do not have any block evaluation preference (e.g. default tensor
+  // expression with raw buffer access).
+  static TensorBlockV2ResourceRequirements any() {
+    return {TensorBlockV2ShapeType::kUniformAllDims, 1};
+  }
+
+private:
+  using Requirements = TensorBlockV2ResourceRequirements;
+
+  static size_t merge(size_t lhs_size, size_t rhs_size) {
+    return numext::maxi(lhs_size, rhs_size);
+  }
+
+  static TensorBlockV2ShapeType merge(TensorBlockV2ShapeType lhs,
+                                      TensorBlockV2ShapeType rhs) {
+    return (lhs == TensorBlockV2ShapeType::kSkewedInnerDims ||
+            rhs == TensorBlockV2ShapeType::kSkewedInnerDims)
+               ? TensorBlockV2ShapeType::kSkewedInnerDims
+               : TensorBlockV2ShapeType::kUniformAllDims;
+  }
+};
+
 // -------------------------------------------------------------------------- //
 // TensorBlockDescriptor specifies a block offset within a tensor and the block
 // sizes along each of the tensor dimensions.