Add support for arbitrary parameters for CPU Gather

* The shape of input and indices tensors, and the gather axis
  can be any number, as long as these are valid and the output
  tensor doesn't have more dimensions than the library supports.
* Update the reference code to be more generic and straightforward.
* Add necessary test cases.

Signed-off-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Resolves: COMPMID-5919
Change-Id: Ic7e2032777aa97ecc147f61d5388528697508ab1
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9199
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Gunes Bayir <gunes.bayir@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>

3 files changed, 61 insertions, 37 deletions

diff --git a/arm_compute/core/Helpers.h b/arm_compute/core/Helpers.h
index fd6e94c079..f19e1e12e0 100644
--- a/arm_compute/core/Helpers.h
+++ b/arm_compute/core/Helpers.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2021 Arm Limited.
+ * Copyright (c) 2016-2021, 2023 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -55,6 +55,16 @@ public:
      */
     Iterator(const ITensor *tensor, const Window &window);
 
+    /** Create a container iterator for the tensor with the specified number of dimensions, stride, buffer pointer and window.
+     *
+     * @param[in] num_dims The number of dimensions.
+     * @param[in] strides  The strides in bytes.
+     * @param[in] buffer   The data buffer.
+     * @param[in] offset   The offset in bytes from the beginning of the buffer to the first element of the tensor.
+     * @param[in] window   The window which will be used to iterate over the tensor.
+     */
+    Iterator(size_t num_dims, const Strides &strides, uint8_t *buffer, size_t offset, const Window &window);
+
     /** Increment the iterator along the specified dimension of the step value associated to the dimension.
      *
      * @warning It is the caller's responsibility to call increment(dimension+1) when reaching the end of a dimension, the iterator will not check for overflow.
@@ -86,6 +96,17 @@ public:
     void reset(size_t dimension);
 
 private:
+
+    /** Initialize a container iterator for the tensor with the specified number of dimensions, stride, buffer pointer and window.
+     *
+     * @param[in] num_dims The number of dimensions.
+     * @param[in] strides  The strides in bytes.
+     * @param[in] buffer   The data buffer.
+     * @param[in] offset   The offset in bytes from the beginning of the buffer to the first element of the tensor.
+     * @param[in] window   The window which will be used to iterate over the tensor.
+     */
+    void initialize(size_t num_dims, const Strides &strides, uint8_t *buffer, size_t offset, const Window &window);
+
     uint8_t *_ptr;
 
     class Dimension
diff --git a/arm_compute/core/Helpers.inl b/arm_compute/core/Helpers.inl
index a910521f94..ff902bba20 100644
--- a/arm_compute/core/Helpers.inl
+++ b/arm_compute/core/Helpers.inl
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2021 Arm Limited.
+ * Copyright (c) 2016-2021, 2023 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -98,13 +98,23 @@ inline Iterator::Iterator(const ITensor *tensor, const Window &win)
     ARM_COMPUTE_ERROR_ON(tensor == nullptr);
     ARM_COMPUTE_ERROR_ON(tensor->info() == nullptr);
 
-    const ITensorInfo *info    = tensor->info();
-    const Strides     &strides = info->strides_in_bytes();
+    initialize(tensor->info()->num_dimensions(), tensor->info()->strides_in_bytes(), tensor->buffer(), tensor->info()->offset_first_element_in_bytes(), win);
+}
+
+inline Iterator::Iterator(size_t num_dims, const Strides &strides, uint8_t *buffer, size_t offset, const Window &win)
+    : Iterator()
+{
+    initialize(num_dims, strides, buffer, offset, win);
+}
+
+inline void Iterator::initialize(size_t num_dims, const Strides &strides, uint8_t *buffer, size_t offset, const Window &win)
+{
+    ARM_COMPUTE_ERROR_ON(buffer == nullptr);
 
-    _ptr = tensor->buffer() + info->offset_first_element_in_bytes();
+    _ptr = buffer + offset;
 
     //Initialize the stride for each dimension and calculate the position of the first element of the iteration:
-    for(unsigned int n = 0; n < info->num_dimensions(); ++n)
+    for(unsigned int n = 0; n < num_dims; ++n)
     {
         _dims[n]._stride = win[n].step() * strides[n];
         std::get<0>(_dims)._dim_start += static_cast<size_t>(strides[n]) * win[n].start();
@@ -116,7 +126,7 @@ inline Iterator::Iterator(const ITensor *tensor, const Window &win)
         _dims[n]._dim_start = std::get<0>(_dims)._dim_start;
     }
 
-    ARM_COMPUTE_ERROR_ON_WINDOW_DIMENSIONS_GTE(win, info->num_dimensions());
+    ARM_COMPUTE_ERROR_ON_WINDOW_DIMENSIONS_GTE(win, num_dims);
 }
 
 inline void Iterator::increment(const size_t dimension)
diff --git a/arm_compute/core/utils/misc/ShapeCalculator.h b/arm_compute/core/utils/misc/ShapeCalculator.h
index 9e7c981814..94bd3aca03 100644
--- a/arm_compute/core/utils/misc/ShapeCalculator.h
+++ b/arm_compute/core/utils/misc/ShapeCalculator.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2022 Arm Limited.
+ * Copyright (c) 2017-2023 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -1537,39 +1537,32 @@ inline TensorShape compute_pool3d_shape(const TensorShape &src, Pooling3dLayerIn
  */
 inline TensorShape compute_gather_shape(const TensorShape &input_shape, const TensorShape &indices_shape, uint32_t actual_axis)
 {
-    ARM_COMPUTE_ERROR_ON(input_shape.num_dimensions() > 4);
-    ARM_COMPUTE_ERROR_ON(actual_axis >= input_shape.num_dimensions());
-    ARM_COMPUTE_ERROR_ON(indices_shape.num_dimensions() > 3);
-    TensorShape output_shape = input_shape;
-    if(indices_shape.num_dimensions() == 1u)
+    const auto input_num_dims = input_shape.num_dimensions();
+    const auto indices_num_dims = indices_shape.num_dimensions();
+
+    ARM_COMPUTE_ERROR_ON(actual_axis >= input_num_dims);
+    ARM_COMPUTE_ERROR_ON(input_num_dims + indices_num_dims - 1 > Coordinates::num_max_dimensions);
+
+    TensorShape output_shape;
+    size_t dim_no = 0;
+
+    for(; dim_no < actual_axis; ++dim_no)
     {
-        output_shape[actual_axis] = indices_shape[0];
+        output_shape.set(dim_no, input_shape[dim_no]);
     }
-    else
+
+    for(; dim_no < actual_axis + indices_num_dims; ++dim_no)
     {
-        const auto ind_num_dims
-        {
-            indices_shape.num_dimensions()
-        };
-        output_shape.shift_right(ind_num_dims - 1);
-        switch(actual_axis)
-        {
-            case 1:
-            {
-                output_shape[0] = input_shape[0];
-                for(size_t idx = 0; idx < ind_num_dims; ++idx)
-                {
-                    output_shape.set(actual_axis + idx, indices_shape[idx], false);
-                }
-                break;
-            }
-            default:
-            {
-                // 2d and 3d indices are only supported for axis == 1
-                ARM_COMPUTE_ERROR_ON(actual_axis != 1 && indices_shape.num_dimensions() > 1);
-            }
-        }
+        output_shape.set(dim_no, indices_shape[dim_no - actual_axis]);
+    }
+
+    for(; dim_no < input_num_dims + indices_num_dims - 1; ++dim_no)
+    {
+        output_shape.set(dim_no, input_shape[dim_no + 1 - indices_num_dims]);
     }
+
+    ARM_COMPUTE_ERROR_ON(input_shape.total_size() * indices_shape.total_size() != output_shape.total_size() * input_shape[actual_axis]);
+
     return output_shape;
 }
 } // namespace shape_calculator