[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/thrust/testing/max_element.cu

@@ -0,0 +1,122 @@
+#include <thrust/extrema.h>
+#include <thrust/functional.h>
+#include <thrust/iterator/retag.h>
+#include <thrust/iterator/transform_iterator.h>
+
+#include <cuda/iterator>
+
+#include <unittest/unittest.h>
+
+template <class Vector>
+void TestMaxElementSimple()
+{
+  using T = typename Vector::value_type;
+
+  Vector data{3, 5, 1, 2, 5, 1};
+
+  ASSERT_EQUAL(*thrust::max_element(data.begin(), data.end()), 5);
+  ASSERT_EQUAL(thrust::max_element(data.begin(), data.end()) - data.begin(), 1);
+
+  ASSERT_EQUAL(*thrust::max_element(data.begin(), data.end(), ::cuda::std::greater<T>()), 1);
+  ASSERT_EQUAL(thrust::max_element(data.begin(), data.end(), ::cuda::std::greater<T>()) - data.begin(), 2);
+}
+DECLARE_VECTOR_UNITTEST(TestMaxElementSimple);
+
+template <class Vector>
+void TestMaxElementWithTransform()
+{
+  using T = typename Vector::value_type;
+
+  Vector data{3, 5, 1, 2, 5, 1};
+
+  ASSERT_EQUAL(*thrust::max_element(thrust::make_transform_iterator(data.begin(), ::cuda::std::negate<T>()),
+                                    thrust::make_transform_iterator(data.end(), ::cuda::std::negate<T>())),
+               -1);
+  ASSERT_EQUAL(*thrust::max_element(thrust::make_transform_iterator(data.begin(), ::cuda::std::negate<T>()),
+                                    thrust::make_transform_iterator(data.end(), ::cuda::std::negate<T>()),
+                                    ::cuda::std::greater<T>()),
+               -5);
+}
+DECLARE_VECTOR_UNITTEST(TestMaxElementWithTransform);
+
+template <typename T>
+void TestMaxElement(const size_t n)
+{
+  thrust::host_vector<T> h_data   = unittest::random_samples<T>(n);
+  thrust::device_vector<T> d_data = h_data;
+
+  typename thrust::host_vector<T>::iterator h_max   = thrust::max_element(h_data.begin(), h_data.end());
+  typename thrust::device_vector<T>::iterator d_max = thrust::max_element(d_data.begin(), d_data.end());
+
+  ASSERT_EQUAL(h_max - h_data.begin(), d_max - d_data.begin());
+
+  typename thrust::host_vector<T>::iterator h_min =
+    thrust::max_element(h_data.begin(), h_data.end(), ::cuda::std::greater<T>());
+  typename thrust::device_vector<T>::iterator d_min =
+    thrust::max_element(d_data.begin(), d_data.end(), ::cuda::std::greater<T>());
+
+  ASSERT_EQUAL(h_min - h_data.begin(), d_min - d_data.begin());
+}
+DECLARE_VARIABLE_UNITTEST(TestMaxElement);
+
+template <typename ForwardIterator>
+ForwardIterator max_element(my_system& system, ForwardIterator first, ForwardIterator)
+{
+  system.validate_dispatch();
+  return first;
+}
+
+void TestMaxElementDispatchExplicit()
+{
+  thrust::device_vector<int> vec(1);
+
+  my_system sys(0);
+  thrust::max_element(sys, vec.begin(), vec.end());
+
+  ASSERT_EQUAL(true, sys.is_valid());
+}
+DECLARE_UNITTEST(TestMaxElementDispatchExplicit);
+
+template <typename ForwardIterator>
+ForwardIterator max_element(my_tag, ForwardIterator first, ForwardIterator)
+{
+  *first = 13;
+  return first;
+}
+
+void TestMaxElementDispatchImplicit()
+{
+  thrust::device_vector<int> vec(1);
+
+  thrust::max_element(thrust::retag<my_tag>(vec.begin()), thrust::retag<my_tag>(vec.end()));
+
+  ASSERT_EQUAL(13, vec.front());
+}
+DECLARE_UNITTEST(TestMaxElementDispatchImplicit);
+
+void TestMaxElementWithBigIndexesHelper(int magnitude)
+{
+  thrust::counting_iterator<long long> begin(1);
+  thrust::counting_iterator<long long> end = begin + (1ll << magnitude);
+  ASSERT_EQUAL(::cuda::std::distance(begin, end), 1ll << magnitude);
+
+  ASSERT_EQUAL(*thrust::max_element(thrust::device, begin, end), (1ll << magnitude));
+}
+
+void TestMaxElementWithBigIndexes()
+{
+  TestMaxElementWithBigIndexesHelper(30);
+#ifndef THRUST_FORCE_32_BIT_OFFSET_TYPE
+  TestMaxElementWithBigIndexesHelper(31);
+  TestMaxElementWithBigIndexesHelper(32);
+  TestMaxElementWithBigIndexesHelper(33);
+#endif
+}
+DECLARE_UNITTEST(TestMaxElementWithBigIndexes);
+
+void TestMaxElementCudaIterator()
+{
+  auto pos = thrust::max_element(thrust::device, cuda::counting_iterator{0}, cuda::counting_iterator{0} + 100);
+  ASSERT_EQUAL(*pos, 99);
+}
+DECLARE_UNITTEST(TestMaxElementCudaIterator);