Clean up portable op_topk

The comparison function was repeated several times. Factor it out.

Differential Revision: [D67875394](https://our.internmc.facebook.com/intern/diff/D67875394/)

ghstack-source-id: 260406714
Pull Request resolved: #7528

Author: swolchok

kernels/portable/cpu/op_topk.cpp

@@ -50,6 +50,14 @@ bool get_topk_target_size(
   return true;
 }
 
+template <typename T>
+bool float_less_than(T x, T y) {
+  if constexpr (std::is_integral_v<T>) {
+    return x < y;
+  }
+  return (!std::isnan(x) && std::isnan(y)) || x < y;
+}
+
 template <typename CTYPE, typename elem_t = std::pair<CTYPE, int64_t>>
 void perform_topk(
     const Tensor& in,
@@ -101,69 +109,19 @@ void perform_topk(
       }
 
       // Perform topk on the queue
+      const auto elem_greater = [](const elem_t& x, const elem_t& y) -> bool {
+        return float_less_than(y.first, x.first);
+      };
+      const auto elem_less = [](const elem_t& x, const elem_t& y) -> bool {
+        return float_less_than(x.first, y.first);
+      };
+      const auto cmp = largest ? elem_greater : elem_less;
       if (use_partial_sort) {
-        if (largest) {
-          std::partial_sort(
-              queue,
-              queue + k,
-              queue + dim_size,
-              [](const elem_t& x, const elem_t& y) -> bool {
-                return (
-                    (std::isnan(x.first) && !std::isnan(y.first)) ||
-                    (x.first > y.first));
-              });
-        } else {
-          std::partial_sort(
-              queue,
-              queue + k,
-              queue + dim_size,
-              [](const elem_t& x, const elem_t& y) -> bool {
-                return (
-                    (!std::isnan(x.first) && std::isnan(y.first)) ||
-                    (x.first < y.first));
-              });
-        }
+        std::partial_sort(queue, queue + k, queue + dim_size, cmp);
       } else {
-        if (largest) {
-          std::nth_element(
-              queue,
-              queue + k - 1,
-              queue + dim_size,
-              [](const elem_t& x, const elem_t& y) -> bool {
-                return (
-                    (std::isnan(x.first) && !std::isnan(y.first)) ||
-                    (x.first > y.first));
-              });
-          if (sorted) {
-            std::sort(
-                queue,
-                queue + k - 1,
-                [](const elem_t& x, const elem_t& y) -> bool {
-                  return (
-                      (std::isnan(x.first) && !std::isnan(y.first)) ||
-                      (x.first > y.first));
-                });
-          }
-        } else {
-          std::nth_element(
-              queue,
-              queue + k - 1,
-              queue + dim_size,
-              [](const elem_t& x, const elem_t& y) -> bool {
-                return (
-                    (!std::isnan(x.first) && std::isnan(y.first)) ||
-                    (x.first < y.first));
-              });
-          if (sorted) {
-            std::sort(
-                queue,
-                queue + k - 1,
-                [](const elem_t& x, const elem_t& y) -> bool {
-                  return (
-                      (!std::isnan(x.first) && std::isnan(y.first)) ||
-                      (x.first < y.first));
-                });
-          }
+        std::nth_element(queue, queue + k - 1, queue + dim_size, cmp);
+        if (sorted) {
+          std::sort(queue, queue + k - 1, cmp);
         }
       }
 

kernels/test/op_topk_test.cpp

@@ -15,6 +15,8 @@
 
 #include <gtest/gtest.h>
 
+#include <algorithm>
+
 using namespace ::testing;
 using exec_aten::IntArrayRef;
 using exec_aten::ScalarType;
@@ -135,4 +137,32 @@ TEST_F(OpTopkValuesTest, SmokeTest) {
   op_topk_values(input, k, dim, largest, sorted, values, indices);
   EXPECT_TENSOR_CLOSE(values, values_expected);
   EXPECT_TENSOR_EQ(indices, indices_expected);
+
+  largest = false;
+  values_expected = tfFloat.make({2, 2, 2}, {1, 2, 3, 4, 5, 6, 7, 8});
+  indices_expected = tfLong.make({2, 2, 2}, {0, 0, 0, 0, 1, 1, 1, 1});
+  op_topk_values(input, k, dim, largest, sorted, values, indices);
+  EXPECT_TENSOR_CLOSE(values, values_expected);
+  EXPECT_TENSOR_EQ(indices, indices_expected);
+}
+
+TEST_F(OpTopkValuesTest, NonPartialSort) {
+  TensorFactory<ScalarType::Float> tfFloat;
+  TensorFactory<ScalarType::Long> tfLong;
+
+  std::vector<float> data(100);
+  std::iota(data.begin(), data.end(), 0);
+
+  for (const bool largest : {true, false}) {
+    Tensor input = tfFloat.make({(int)data.size()}, data);
+    Tensor values = tfFloat.zeros({1});
+    Tensor indices = tfLong.zeros({1});
+    Tensor values_expected =
+        tfFloat.make({1}, {largest ? data.back() : data.front()});
+    Tensor indices_expected =
+        tfLong.make({1}, {largest ? (long)data.size() - 1 : 0L});
+    op_topk_values(input, 1, 0, largest, true, values, indices);
+    EXPECT_TENSOR_CLOSE(values, values_expected);
+    EXPECT_TENSOR_EQ(indices, indices_expected);
+  }
 }