[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/cuda/reduce_into.cu

@@ -0,0 +1,124 @@
+#include <thrust/execution_policy.h>
+#include <thrust/reduce.h>
+
+#include <cuda/iterator>
+
+#include <unittest/unittest.h>
+
+template <typename ExecutionPolicy, typename InputIter, typename OutputIter, typename T>
+__global__ void reduce_into_kernel(ExecutionPolicy exec, InputIter first, InputIter last, OutputIter result, T init)
+{
+  thrust::reduce_into(exec, first, last, result, init);
+}
+
+#ifdef THRUST_TEST_DEVICE_SIDE
+template <typename T, typename ExecutionPolicy>
+void TestReduceIntoDevice(ExecutionPolicy exec, const size_t n)
+{
+  thrust::host_vector<T> h_data   = unittest::random_integers<T>(n);
+  thrust::device_vector<T> d_data = h_data;
+
+  thrust::host_vector<T> h_result(1);
+  thrust::device_vector<T> d_result(1);
+
+  T init = 13;
+
+  thrust::reduce_into(h_data.begin(), h_data.end(), h_result.begin(), init);
+
+  reduce_into_kernel<<<1, 1>>>(exec, d_data.begin(), d_data.end(), d_result.begin(), init);
+  cudaError_t const err = cudaDeviceSynchronize();
+  ASSERT_EQUAL(cudaSuccess, err);
+
+  ASSERT_EQUAL(h_result, d_result);
+}
+
+template <typename T>
+struct TestReduceIntoDeviceSeq
+{
+  void operator()(const size_t n)
+  {
+    TestReduceIntoDevice<T>(thrust::seq, n);
+  }
+};
+VariableUnitTest<TestReduceIntoDeviceSeq, IntegralTypes> TestReduceIntoDeviceSeqInstance;
+
+template <typename T>
+struct TestReduceIntoDeviceDevice
+{
+  void operator()(const size_t n)
+  {
+    TestReduceIntoDevice<T>(thrust::device, n);
+  }
+};
+VariableUnitTest<TestReduceIntoDeviceDevice, IntegralTypes> TestReduceIntoDeviceDeviceInstance;
+
+template <typename T>
+struct TestReduceIntoDeviceNoSync
+{
+  void operator()(const size_t n)
+  {
+    TestReduceIntoDevice<T>(thrust::cuda::par_nosync, n);
+  }
+};
+VariableUnitTest<TestReduceIntoDeviceNoSync, IntegralTypes> TestReduceIntoDeviceNoSyncInstance;
+#endif
+
+template <typename ExecutionPolicy>
+void TestReduceIntoCudaStreams(ExecutionPolicy policy)
+{
+  using Vector = thrust::device_vector<int>;
+
+  Vector v = {1, -2, 3};
+
+  Vector o(1);
+
+  cudaStream_t s;
+  cudaStreamCreate(&s);
+
+  auto streampolicy = policy.on(s);
+
+  // no initializer
+  thrust::reduce_into(streampolicy, v.begin(), v.end(), o.begin());
+
+  cudaStreamSynchronize(s);
+  ASSERT_EQUAL(o[0], 2);
+
+  // with initializer
+  thrust::reduce_into(streampolicy, v.begin(), v.end(), o.begin(), 10);
+
+  cudaStreamSynchronize(s);
+  ASSERT_EQUAL(o[0], 12);
+
+  cudaStreamDestroy(s);
+}
+
+void TestReduceIntoCudaStreamsSync()
+{
+  TestReduceIntoCudaStreams(thrust::cuda::par);
+}
+DECLARE_UNITTEST(TestReduceIntoCudaStreamsSync);
+
+void TestReduceIntoCudaStreamsNoSync()
+{
+  TestReduceIntoCudaStreams(thrust::cuda::par_nosync);
+}
+DECLARE_UNITTEST(TestReduceIntoCudaStreamsNoSync);
+
+#if defined(THRUST_RDC_ENABLED)
+void TestReduceIntoLargeInput()
+{
+  using T                 = unsigned long long;
+  using OffsetT           = std::size_t;
+  const OffsetT num_items = 1ull << 32;
+
+  cuda::constant_iterator<T> d_data(T{1});
+  thrust::device_vector<T> d_result(1);
+
+  reduce_into_kernel<<<1, 1>>>(thrust::device, d_data, d_data + num_items, d_result.begin(), T{});
+  cudaError_t const err = cudaDeviceSynchronize();
+  ASSERT_EQUAL(cudaSuccess, err);
+
+  ASSERT_EQUAL(num_items, d_result[0]);
+}
+DECLARE_UNITTEST(TestReduceIntoLargeInput);
+#endif