arm_compute v19.11
diff --git a/src/runtime/CL/functions/CLReductionOperation.cpp b/src/runtime/CL/functions/CLReductionOperation.cpp
index 38f0a75..3aa5a81 100644
--- a/src/runtime/CL/functions/CLReductionOperation.cpp
+++ b/src/runtime/CL/functions/CLReductionOperation.cpp
@@ -26,15 +26,17 @@
 #include "arm_compute/core/CL/ICLTensor.h"
 #include "arm_compute/core/CL/kernels/CLReductionOperationKernel.h"
 #include "arm_compute/core/Error.h"
+#include "arm_compute/core/Helpers.h"
 #include "arm_compute/core/PixelValue.h"
 #include "arm_compute/core/TensorInfo.h"
 #include "arm_compute/core/Validate.h"
+#include "arm_compute/core/utils/misc/ShapeCalculator.h"
 #include "arm_compute/runtime/CL/CLScheduler.h"
 #include "arm_compute/runtime/Tensor.h"
 #include "support/ToolchainSupport.h"
 
-using namespace arm_compute;
-
+namespace arm_compute
+{
 namespace
 {
 unsigned int calculate_number_of_stages(const ITensorInfo *input, unsigned int axis)
@@ -56,17 +58,52 @@
 } // namespace
 
 CLReductionOperation::CLReductionOperation(std::shared_ptr<IMemoryManager> memory_manager)
-    : _memory_group(std::move(memory_manager)), _results_vector(), _reduction_kernels_vector(), _border_handlers_vector(), _num_of_stages(), _reduction_axis(), _is_serial()
+    : _memory_group(std::move(memory_manager)), _results_vector(), _reduction_kernels_vector(), _border_handlers_vector(), _reshape_kernel(), _op(), _num_of_stages(), _reduction_axis(), _is_serial(),
+      _is_reshape_required(false)
 {
 }
 
-Status CLReductionOperation::validate(const ITensorInfo *input, const ITensorInfo *output, unsigned int axis, ReductionOperation op)
+Status CLReductionOperation::validate(const ITensorInfo *input, const ITensorInfo *output, unsigned int axis, ReductionOperation op, bool keep_dims)
 {
-    const unsigned int num_of_stages = calculate_number_of_stages(input, axis);
-    bool               is_serial     = is_data_type_quantized(input->data_type()) || axis != 0;
+    ARM_COMPUTE_RETURN_ERROR_ON_MSG(axis >= TensorShape::num_max_dimensions, "Reduction axis greater than max number of dimensions");
+    ARM_COMPUTE_RETURN_ERROR_ON_MSG(axis > 3, "Unsupported reduction axis");
+
+    const unsigned int num_of_stages       = calculate_number_of_stages(input, axis);
+    const bool         is_serial           = needs_serialized_reduction(op, input->data_type(), axis);
+    const bool         is_arg_min_max      = (op == ReductionOperation::ARG_IDX_MAX) || (op == ReductionOperation::ARG_IDX_MIN);
+    const bool         is_reshape_required = !keep_dims || is_arg_min_max;
+
+    if(is_reshape_required)
+    {
+        const TensorInfo expected_output_shape = output->clone()->set_tensor_shape(arm_compute::misc::shape_calculator::compute_reduced_shape(input->tensor_shape(), axis, keep_dims));
+        ARM_COMPUTE_RETURN_ERROR_ON_MISMATCHING_SHAPES(&expected_output_shape, output);
+    }
+
+    auto *output_internal = output;
+
+    TensorInfo output_before_reshape;
+    const auto input_shape        = input->tensor_shape();
+    const auto input_data_type    = input->data_type();
+    const auto input_num_channles = input->num_channels();
+    const auto input_qinfo        = input->quantization_info();
+    const auto output_data_type   = is_arg_min_max ? DataType::S32 : output->data_type();
+
+    auto initialize_tensorinfo = [](TensorInfo & ti, TensorShape shape, DataType data_type, int num_channels, QuantizationInfo qinfo)
+    {
+        ti.set_data_type(data_type).set_tensor_shape(shape).set_num_channels(num_channels).set_quantization_info(qinfo);
+    };
+
+    if(is_reshape_required)
+    {
+        auto shape_before_reshape = input_shape;
+        shape_before_reshape.set(axis, 1);
+        initialize_tensorinfo(output_before_reshape, shape_before_reshape, output_data_type, input_num_channles, input_qinfo);
+        output_internal = &output_before_reshape;
+    }
+
     if(is_serial)
     {
-        ARM_COMPUTE_RETURN_ON_ERROR(CLReductionOperationKernel::validate(input, output, axis, op));
+        ARM_COMPUTE_RETURN_ON_ERROR(CLReductionOperationKernel::validate(input, output_internal, axis, op));
     }
     else
     {
@@ -74,14 +111,13 @@
         std::vector<TensorInfo> sums_vector(num_of_stages - 1);
 
         // Create intermediate tensor info
-        TensorShape shape{ input->tensor_shape() };
+        TensorShape shape{ input_shape };
+
+        shape.set(0, ceil(shape.x() / 128.f));
 
         for(unsigned int i = 0; i < num_of_stages - 1; i++)
         {
-            shape.set(0, ceil(shape.x() / 128.f));
-            sums_vector[i].set_data_type(input->data_type());
-            sums_vector[i].set_tensor_shape(shape);
-            sums_vector[i].set_num_channels(input->num_channels());
+            initialize_tensorinfo(sums_vector[i], shape, input_data_type, input_num_channles, input_qinfo);
         }
 
         ReductionOperation first_kernel_op;
@@ -130,17 +166,72 @@
 
         // Validate ReductionOperation on the last stage
         const unsigned int last_stage = num_of_stages - 1;
-        ARM_COMPUTE_RETURN_ON_ERROR(CLReductionOperationKernel::validate(&sums_vector[last_stage - 1], output, axis, last_kernel_op, input->dimension(0)));
+        ARM_COMPUTE_RETURN_ON_ERROR(CLReductionOperationKernel::validate(&sums_vector[last_stage - 1], output_internal, axis, last_kernel_op, input->dimension(0)));
+    }
+
+    if(is_reshape_required)
+    {
+        ARM_COMPUTE_RETURN_ON_ERROR(CLReshapeLayerKernel::validate(output_internal, output));
     }
 
     return Status{};
 }
 
-void CLReductionOperation::configure(ICLTensor *input, ICLTensor *output, unsigned int axis, ReductionOperation op)
+ICLTensor *CLReductionOperation::configure_intermediate_result_vector(ICLTensor *input, ICLTensor *output)
 {
-    _num_of_stages  = calculate_number_of_stages(input->info(), axis);
-    _reduction_axis = axis;
-    _is_serial      = is_data_type_quantized(input->info()->data_type()) || axis != 0;
+    if(!_is_reshape_required && _is_serial)
+    {
+        return output;
+    }
+
+    auto       intermediate_result_vector_size = _is_serial ? 1 : _num_of_stages;
+    const auto is_arg_min_max                  = (_op == ReductionOperation::ARG_IDX_MAX || _op == ReductionOperation::ARG_IDX_MIN);
+
+    if(!_is_reshape_required)
+    {
+        --intermediate_result_vector_size;
+    }
+
+    _results_vector.resize(intermediate_result_vector_size);
+    auto shape = input->info()->tensor_shape();
+
+    shape.set(_reduction_axis, _is_serial ? 1 : ceil(shape.x() / 128.f));
+
+    for(auto &v : _results_vector)
+    {
+        if(&v == &_results_vector.back() && _is_reshape_required)
+        {
+            shape.set(_reduction_axis, 1);
+        }
+        v.allocator()->init(input->info()->clone()->set_tensor_shape(shape));
+    }
+
+    if(is_arg_min_max)
+    {
+        _results_vector.back().info()->set_data_type(DataType::S32).set_is_resizable(true).reset_padding();
+    }
+
+    return _is_reshape_required ? &_results_vector.back() : output;
+}
+
+void CLReductionOperation::configure(ICLTensor *input, ICLTensor *output, unsigned int axis, ReductionOperation op, bool keep_dims)
+{
+    _op                       = op;
+    _num_of_stages            = calculate_number_of_stages(input->info(), axis);
+    _reduction_axis           = axis;
+    _is_serial                = needs_serialized_reduction(op, input->info()->data_type(), axis);
+    const bool is_arg_min_max = (op == ReductionOperation::ARG_IDX_MAX) || (op == ReductionOperation::ARG_IDX_MIN);
+    _is_reshape_required      = !keep_dims || is_arg_min_max;
+
+    auto *output_internal = configure_intermediate_result_vector(input, output);
+
+    // ArgMinMax might not give initialized output tensor, so initialize here.
+    if(_is_reshape_required)
+    {
+        const TensorShape output_shape     = arm_compute::misc::shape_calculator::compute_reduced_shape(input->info()->tensor_shape(), axis, false);
+        const auto        output_data_type = is_arg_min_max ? DataType::S32 : input->info()->data_type();
+        auto_init_if_empty(*output->info(), input->info()->clone()->set_tensor_shape(output_shape).set_data_type(output_data_type).reset_padding().set_is_resizable(true));
+    }
 
     // Configure reduction operation kernels
     _reduction_kernels_vector.resize(_num_of_stages);
@@ -148,20 +239,16 @@
     // Create temporary tensors
     if(_is_serial)
     {
-        _reduction_kernels_vector[0].configure(input, output, axis, op, 0);
+        if(_is_reshape_required)
+        {
+            _memory_group.manage(&_results_vector.back());
+        }
+
+        _reduction_kernels_vector[0].configure(input, output_internal, axis, op, 0);
     }
     else
     {
         _border_handlers_vector.resize(_num_of_stages);
-        _results_vector.resize(_num_of_stages - 1);
-        TensorShape shape{ input->info()->tensor_shape() };
-        for(unsigned int i = 0; i < _num_of_stages - 1; i++)
-        {
-            shape.set(0, ceil(shape.x() / 128.f));
-            _results_vector[i].allocator()->init(input->info()->clone()->set_tensor_shape(shape));
-        }
-
-        // Apply ReductionOperation only on first kernel
         _memory_group.manage(&_results_vector[0]);
 
         ReductionOperation first_kernel_op;
@@ -262,10 +349,22 @@
         // Apply ReductionOperation on the last stage
         const unsigned int last_stage  = _num_of_stages - 1;
         const unsigned int input_width = input->info()->dimension(0);
-        _reduction_kernels_vector[last_stage].configure(&_results_vector[last_stage - 1], output, axis, last_kernel_op, input_width);
+
+        if(_is_reshape_required)
+        {
+            _memory_group.manage(&_results_vector.back());
+        }
+
+        _reduction_kernels_vector[last_stage].configure(&_results_vector[last_stage - 1], output_internal, axis, last_kernel_op, input_width);
         _border_handlers_vector[last_stage].configure(&_results_vector[last_stage - 1], _reduction_kernels_vector[last_stage].border_size(), BorderMode::CONSTANT, pixelValue);
         _results_vector[last_stage - 1].allocator()->allocate();
     }
+
+    if(_is_reshape_required)
+    {
+        _reshape_kernel.configure(&_results_vector.back(), output);
+        _results_vector.back().allocator()->allocate();
+    }
 }
 
 void CLReductionOperation::run()
@@ -284,4 +383,10 @@
             CLScheduler::get().enqueue(_reduction_kernels_vector[i], false);
         }
     }
+
+    if(_is_reshape_required)
+    {
+        CLScheduler::get().enqueue(_reshape_kernel, false);
+    }
 }
+} // namespace arm_compute