[oleksandr-pavlyk]

Description

This PR is a split from #11374 and changes non-API tests for DeviceSegmentedScan algorithm to use C2H buffer utilities and CCCL Runtime API.

Closes #12580

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

No actionable comments were generated in the recent review.

Summary

Summary by CodeRabbit

• Tests
  • Updated segmented-scan tests to use explicit CUDA streams and buffer-based input and output checks across standard, multi-segment, noncommutative, and environment-based cases.
  • Added coverage for queued input preparation and exclusive-sum results, and retained checks for in-place scans, tuning configurations, custom streams, and default-stream behavior.
  • Added a reusable utility for generating test inputs in host buffers.

The segmented-scan tests replace Thrust-backed containers with CUDA buffers and raw pointers. They pass explicit streams to scan calls, use stream-aware copies and comparisons, and add a host-buffer generator for test inputs.

Changes: Segmented scan test migration

Layer / File(s)	Summary
Segmented-scan API test coverage cub/test/catch2_test_device_segmented_scan.cu	The API tests use host and device buffers, pass streams to scan operations, and verify output through host pointers. They retain coverage for scan variants, offset APIs, and matching-type in-place scans.
Environment and tuning tests cub/test/catch2_test_device_segmented_scan_env.cu	Environment and tuning tests use C2H buffers and device pointers. The tests include stream-ordering coverage and read tuning selections through the stream.
Two-phase scans across stream modes cub/test/catch2_test_device_segmented_scan_env.cu	Two-phase tests use device pointers and stream-aware comparisons for custom streams, legacy null-stream cases, and tuning cases.
Multi-segment dispatch and scan cases cub/test/catch2_test_device_segmented_scan_multi_segment.cu	Dispatch helpers accept streams and device buffers. Noncommutative and integer scan cases use host/device buffers and stream-aware output checks.
Empty-segment and iterator cases cub/test/catch2_test_device_segmented_scan_multi_segment.cu	Empty and reversed segment cases retain canary checks with buffer-based setup. Iterator dispatch tests also use stream-aware buffers and comparisons.
Host-buffer generation and noncommutative scan cub/test/catch2_test_device_segmented_scan_utils.cuh, cub/test/catch2_test_device_segmented_scan_noncommutative.cu	A host-buffer tabulation helper is added and used by the noncommutative scan test, which runs and checks results with an explicit stream.

Possibly related issues

• [Task] Open PR with last shard of 10898 which modifies segmented test scan tests #11373 — This PR migrates segmented-scan non-API tests to buffers and explicit streams, matching the issue’s requested final PR in the test migration.
• Change segmented scan tests to use cuda::buffer #10897 — The segmented-scan tests in this PR replace Thrust containers with CUDA and C2H buffers, addressing the issue’s stated migration objective.

Possibly related PRs

• NVIDIA/cccl#9787 — Both PRs change segmented-scan tuning tests.
• NVIDIA/cccl#10898 — This PR continues the segmented-scan test migration to buffers established in that PR.
• NVIDIA/cccl#11374 — Both PRs migrate segmented-scan tests to CUDA buffers and explicit streams.

Suggested reviewers: jacobfaib

Change: Other

Merge Risk: Minimal · up to c6ce6

This PR migrates the segmented-scan tests from Thrust containers to CUDA buffers with explicit streams. No concrete defect was found in the stream ordering or buffer handling, so it looks ready to merge after normal CI.

- [ ] Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

Recent review info

Run configuration

• Source mode: Auto
• Repository: NVIDIA/cccl
• Branch: main
• File: .coderabbit.yaml
• Commit: 0dd2af4
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Enterprise
• Run ID: 094e0955-c7cd-44d8-97a8-dc126a6b2a25

Commits

Reviewing files that changed from the base of the PR and between 0dd2af4 and c6ce670.

Files selected for processing: 5

• cub/test/catch2_test_device_segmented_scan.cu
• cub/test/catch2_test_device_segmented_scan_env.cu
• cub/test/catch2_test_device_segmented_scan_multi_segment.cu
• cub/test/catch2_test_device_segmented_scan_noncommutative.cu
• cub/test/catch2_test_device_segmented_scan_utils.cuh

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