[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/cudax/examples/stf/word_count.cu

@@ -0,0 +1,91 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDASTF in CUDA C++ Core Libraries,
+// under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2022-2024 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+/**
+ * @file
+ * @brief Counting words in a text using a launch kernel
+ */
+
+#include <cuda/experimental/stf.cuh>
+
+using namespace cuda::experimental::stf;
+
+// determines whether the character is alphabetical
+__host__ __device__ bool is_alpha(const char c)
+{
+  return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+}
+
+int main()
+{
+  // Paragraph from 'The Raven' by Edgar Allan Poe
+  // http://en.wikipedia.org/wiki/The_Raven
+  const char raw_input[] =
+    "  But the raven, sitting lonely on the placid bust, spoke only,\n"
+    "  That one word, as if his soul in that one word he did outpour.\n"
+    "  Nothing further then he uttered - not a feather then he fluttered -\n"
+    "  Till I scarcely more than muttered `Other friends have flown before -\n"
+    "  On the morrow he will leave me, as my hopes have flown before.'\n"
+    "  Then the bird said, `Nevermore.'\n";
+
+  context ctx;
+
+  auto ltext = ctx.logical_data(const_cast<char*>(&raw_input[0]), {sizeof(raw_input)});
+
+  int cnt   = 0;
+  auto lcnt = ctx.logical_data(&cnt, {1});
+
+  auto number_devices = 2;
+  auto all_devs       = exec_place::repeat(exec_place::device(0), number_devices);
+
+  auto spec = par(con(128));
+
+  ctx.launch(spec, all_devs, ltext.read(), lcnt.rw())->*[] _CCCL_DEVICE(auto th, auto text, auto cnt) {
+    int local_cnt = 0;
+    for (size_t i = th.rank(); i < text.size() - 1; i += th.size())
+    {
+      /* If the thread encounters the beginning of a new word, increment
+       * its local counter */
+      if (!is_alpha(text(i)) && is_alpha(text(i + 1)))
+      {
+        local_cnt++;
+      }
+    }
+
+    // Get a piece of shared memory, and zero it
+    __shared__ int block_cnt;
+    block_cnt = 0;
+    th.inner().sync();
+
+    // In every block, partial sums are gathered, and added to the result
+    // by the first thread of the block.
+    atomicAdd(&block_cnt, local_cnt);
+    th.inner().sync();
+
+    if (th.inner().rank() == 0)
+    {
+      atomicAdd(&cnt(0), block_cnt);
+    }
+  };
+
+  ctx.finalize();
+
+  int ref_cnt = 0;
+  for (size_t i = 0; i < sizeof(raw_input) - 1; i++)
+  {
+    if (!is_alpha(raw_input[i]) && is_alpha(raw_input[i + 1]))
+    {
+      ref_cnt++;
+    }
+  }
+
+  // fprintf(stderr, "Result : found %d words (expected %d)\n", cnt, ref_cnt);
+  EXPECT(cnt == ref_cnt);
+}