[MPS] Dispatch outer bin edges selection function (#101792)

Dispatch the selection function to prevent using `is_mps()` in `Histogram.cpp`.

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### <samp>🤖 Generated by Copilot at b329a02</samp>

This pull request refactors and implements the logic for inferring the bin edges of histograms from the input tensor for different device types. It introduces a dispatch stub `histogram_select_outer_bin_edges_stub` and moves the device-specific code to separate files, such as `HistogramKernel.cpp` and `HistogramKernel.mm`. This improves the modularity and readability of the histogram functions.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/101792
Approved by: https://github.com/albanD

aten/src/ATen/native/Histogram.cpp

@@ -65,6 +65,7 @@ namespace at { namespace native {
 
 DEFINE_DISPATCH(histogramdd_stub);
 DEFINE_DISPATCH(histogramdd_linear_stub);
+DEFINE_DISPATCH(histogram_select_outer_bin_edges_stub);
 
 namespace {
 
@@ -153,22 +154,6 @@ void histogramdd_prepare_out(const Tensor& input, TensorList bins,
     histogramdd_prepare_out(input, bin_ct, hist, bin_edges);
 }
 
-template<typename scalar_t>
-void infer_bin_edges_from_input(const Tensor& input, const int64_t N,
-        std::vector<double> &leftmost_edges, std::vector<double> &rightmost_edges) {
-    // Calls aminmax on input with dim=0, reducing all but the innermost dimension of input.
-    Tensor min, max;
-    std::tie(min, max) = aminmax(input, 0);
-
-    TORCH_INTERNAL_ASSERT(min.is_contiguous() && max.is_contiguous());
-
-    const scalar_t *min_data = min.data_ptr<scalar_t>();
-    std::copy(min_data, min_data + N, leftmost_edges.begin());
-
-    const scalar_t *max_data = max.data_ptr<scalar_t>();
-    std::copy(max_data, max_data + N, rightmost_edges.begin());
-}
-
 /* Determines the outermost bin edges. For simplicity when calling into aminmax,
  * assumes that input has already been reshaped to (M, N).
  */
@@ -192,19 +177,8 @@ select_outer_bin_edges(const Tensor& input, c10::optional<c10::ArrayRef<double>>
         }
     } else if (input.numel() > 0) {
         // non-empty input
-        AT_DISPATCH_FLOATING_TYPES(input.scalar_type(), "histogramdd", [&]() {
-            if (input.is_mps()) {
-                Tensor min, max;
-                std::tie(min, max) = at::aminmax(input, 0);
 
-                for (const auto i : c10::irange(N)) {
-                    leftmost_edges[i] = min[i].item().to<scalar_t>();
-                    rightmost_edges[i] = max[i].item().to<scalar_t>();
-                }
-            } else {
-                infer_bin_edges_from_input<scalar_t>(input, N, leftmost_edges, rightmost_edges);
-            }
-        });
+        histogram_select_outer_bin_edges_stub(input.device().type(), input, N, leftmost_edges, rightmost_edges);
     }
 
     for (const auto dim : c10::irange(N)) {

aten/src/ATen/native/Histogram.h

@@ -7,8 +7,10 @@ namespace at::native {
 
 using histogramdd_fn = void(*)(const Tensor&, const c10::optional<Tensor>&, bool, Tensor&, const TensorList&);
 using histogramdd_linear_fn = void(*)(const Tensor&, const c10::optional<Tensor>&, bool, Tensor&, const TensorList&, bool);
+using histogram_select_outer_bin_edges_fn = void(*)(const Tensor& input, const int64_t N, std::vector<double> &leftmost_edges, std::vector<double> &rightmost_edges);
 
 DECLARE_DISPATCH(histogramdd_fn, histogramdd_stub);
 DECLARE_DISPATCH(histogramdd_linear_fn, histogramdd_linear_stub);
+DECLARE_DISPATCH(histogram_select_outer_bin_edges_fn, histogram_select_outer_bin_edges_stub);
 
 } // namespace at::native

aten/src/ATen/native/cpu/HistogramKernel.cpp

@@ -10,6 +10,7 @@
 #include <ATen/Functions.h>
 #include <ATen/NativeFunctions.h>
 #else
+#include <ATen/ops/aminmax.h>
 #include <ATen/ops/sum.h>
 #include <ATen/ops/zeros.h>
 #include <ATen/ops/zeros_like_ops.h>
@@ -282,10 +283,33 @@ static void histogramdd_linear_kernel_impl(const Tensor& self, const c10::option
     }
 }
 
+template<typename scalar_t>
+void infer_bin_edges_from_input(const Tensor& input, const int64_t N,
+        std::vector<double> &leftmost_edges, std::vector<double> &rightmost_edges) {
+    // Calls aminmax on input with dim=0, reducing all but the innermost dimension of input.
+    Tensor min, max;
+    std::tie(min, max) = aminmax(input, 0);
+
+    TORCH_INTERNAL_ASSERT(min.is_contiguous() && max.is_contiguous());
+
+    const scalar_t *min_data = min.data_ptr<scalar_t>();
+    std::copy(min_data, min_data + N, leftmost_edges.begin());
+
+    const scalar_t *max_data = max.data_ptr<scalar_t>();
+    std::copy(max_data, max_data + N, rightmost_edges.begin());
+}
+
+static void histogram_select_outer_bin_edges_impl(const Tensor& input, const int64_t N,
+        std::vector<double> &leftmost_edges, std::vector<double> &rightmost_edges) {
+    AT_DISPATCH_FLOATING_TYPES(input.scalar_type(), "histogramdd", [&]() {
+        infer_bin_edges_from_input<scalar_t>(input, N, leftmost_edges, rightmost_edges);
+    });
+}
+
 } // namespace
 
 REGISTER_DISPATCH(histogramdd_stub, &histogramdd_kernel_impl);
-
 REGISTER_DISPATCH(histogramdd_linear_stub, &histogramdd_linear_kernel_impl);
+REGISTER_DISPATCH(histogram_select_outer_bin_edges_stub, &histogram_select_outer_bin_edges_impl);
 
 } // namespace at::native

aten/src/ATen/native/mps/operations/HistogramKernel.mm

@@ -8,6 +8,7 @@
 #include <ATen/Functions.h>
 #include <ATen/NativeFunctions.h>
 #else
+#include <ATen/ops/aminmax.h>
 #include <ATen/ops/sum.h>
 #endif
 
@@ -396,6 +397,20 @@ static void histogramdd_linear_kernel(const Tensor& self,
   }
 }
 
+static void histogram_select_outer_bin_edges_kernel(const Tensor& input,
+                                                    const int64_t N,
+                                                    std::vector<double>& leftmost_edges,
+                                                    std::vector<double>& rightmost_edges) {
+  Tensor min, max;
+  std::tie(min, max) = at::aminmax(input, 0);
+
+  for (const auto i : c10::irange(N)) {
+    leftmost_edges[i] = min[i].item().to<double>();
+    rightmost_edges[i] = max[i].item().to<double>();
+  }
+}
+
 REGISTER_DISPATCH(histogramdd_stub, &histogramdd_kernel);
 REGISTER_DISPATCH(histogramdd_linear_stub, &histogramdd_linear_kernel);
+REGISTER_DISPATCH(histogram_select_outer_bin_edges_stub, &histogram_select_outer_bin_edges_kernel);
 } // namespace at::native