fix omp scan bug by charan-003 · Pull Request #6560 · NVIDIA/cccl

charan-003 · 2025-11-09T09:05:25Z

using the first element of each block as the init value

closes #6317

copy-pr-bot · 2025-11-09T09:05:28Z

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bernhardmgruber · 2025-11-10T09:39:49Z

@charan-003 I added a few more tests.

bernhardmgruber · 2025-11-12T09:47:32Z

/ok to test ae2c2c7

bernhardmgruber · 2025-11-12T19:52:29Z

/ok to test f549d50

bernhardmgruber · 2025-11-13T09:36:49Z

/ok to test b0d8c74

bernhardmgruber · 2025-11-13T15:47:02Z

/ok to test 9ea6902

bernhardmgruber · 2025-11-13T23:47:34Z

@charan-003 I will review this next week.

bernhardmgruber

This is looking good! A few nits, otherwise LGTM!

bernhardmgruber · 2025-11-19T17:52:56Z

/ok to test a8df5c0

bernhardmgruber · 2025-11-19T20:02:43Z

/ok to test 9a7675d

bernhardmgruber · 2025-11-19T23:32:03Z

Thank you so much for taking the time to push the fix through!

bernhardmgruber · 2025-11-19T23:32:19Z

@dkolsen-pgi please re-review and unblock. Thx!

dkolsen-pgi · 2025-11-19T23:49:29Z

  {
-    ::cuda::std::exclusive_scan(block_sums.begin(), block_sums.end(), block_sums.begin(), accum_t{}, wrapped_binary_op);
+    // For no init inclusive scan: exclusive_scan starting at second element with first element as init
+    if (num_threads > 1)


You added the assertion as suggested, but forgot to remove this now unnecessary check for num_threads > 1.

Right, thanks for bringing this up.

bernhardmgruber · 2025-11-20T00:04:25Z

/ok to test 0b1e611

dkolsen-pgi

I only looked at scan.h, not at the tests. That file now looks good.

github-actions · 2025-11-20T01:37:22Z

🥳 CI Workflow Results

🟩 Finished in 1h 30m: Pass: 100%/84 | Total: 14h 28m | Max: 42m 40s | Hits: 88%/116157

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Co-authored-by: Bernhard Manfred Gruber <bernhardmgruber@gmail.com> (cherry picked from commit bb8a5b9)

github-actions · 2025-11-20T01:37:48Z

Successfully created backport PR for branch/3.2.x:

[Backport branch/3.2.x] fix omp scan bug #6704

(cherry picked from commit bb8a5b9) Co-authored-by: charan-003 <yadavcharan003@gmail.com> Co-authored-by: Bernhard Manfred Gruber <bernhardmgruber@gmail.com> Co-authored-by: Elias Stehle <3958403+elstehle@users.noreply.github.com>

…l#6560) (NVIDIA/cccl#6704) Upstream: NVIDIA/cccl@26c79ca HIP counterpart (system/hip): none (rocPRIM scan unaffected). Ported OMP scan fix in system/omp/detail/scan.h: blocks reduce with their first element as init (no accum_t{} identity assumption), no-init inclusive path seeds from block_sums[0] and thread 0 scans without prefix, serial fallback when n < max(threshold, num_threads); _CCCL_ASSERT dropped (not available locally; replaced by a comment). testing/scan.cu and testing/transform_scan.cu gain the new tests (THRUST_HOST_DEVICE spelling; kept local include guards, added <numeric>). test/ counterpart: mirrored in test/test_scan.cpp (Int with friend ops, TestScanWithUserDefinedTypeAndInit replacing TestInclusiveScanWithUserDefinedType, TestScanBug6317 using get_random_data, TestScanEdgeCases) and test/test_transform_scan.cpp (TransformInt, TestTransformScanEdgeCases). Not compiled, tests not run (per human) Co-Authored-By: Claude <noreply@anthropic.com>

…l#6560) Upstream: NVIDIA/cccl@bb8a5b9 - already ported — identical to its `branch/3.2.x` backport 26c79caf60e (NVIDIA/cccl#6704; `+`/`-` lines compared, no difference), ported in ad694ae plus parity fix 5bdd5a9; `thrust/system/omp/detail/scan.h`, `testing/scan.cu` and `testing/transform_scan.cu` already match - HIP counterpart: none (no `thrust/system/cuda/` change) - test/ counterpart: `test/test_scan.cpp` / `test/test_transform_scan.cpp` handled when the backport was ported (ad694ae); no further change - Not compiled, tests not run (autonomous no-build mode) Co-Authored-By: Claude <noreply@anthropic.com>

fix omp scan bug

430a2e8

charan-003 requested a review from a team as a code owner November 9, 2025 09:05

charan-003 requested a review from davebayer November 9, 2025 09:05

github-project-automation Bot added this to CCCL Nov 9, 2025

github-project-automation Bot moved this to Todo in CCCL Nov 9, 2025

cccl-authenticator-app Bot moved this from Todo to In Review in CCCL Nov 9, 2025

dkolsen-pgi requested changes Nov 10, 2025

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Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

github-project-automation Bot moved this from In Review to In Progress in CCCL Nov 10, 2025

Add more scan tests

e400373

bernhardmgruber mentioned this pull request Nov 10, 2025

[BUG]: stdpar multicore scan tests fail at runtime after commit 1238f287f4f654bff12e4d4a29b7dfa1c40a12fe #6317

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charan-003 added 3 commits November 12, 2025 03:08

add scan tests and few changes

656f024

Merge branch 'main' into fix_omp_scan_bug

addf851

Merge branch 'main' into fix_omp_scan_bug

ae2c2c7

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use value type for init accum_t

f549d50

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charan-003 added 2 commits November 12, 2025 15:20

use thrust::inclusive/exclusive

68f500c

Merge branch 'main' into fix_omp_scan_bug

b0d8c74

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fix

9ea6902

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bernhardmgruber reviewed Nov 18, 2025

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Comment thread thrust/testing/transform_scan.cu Resolved

Comment thread thrust/testing/transform_scan.cu Resolved

Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

Comment thread thrust/thrust/system/omp/detail/scan.h Resolved

bernhardmgruber added the backport branch/3.2.x label Nov 18, 2025

minor fix

a8df5c0

bernhardmgruber reviewed Nov 19, 2025

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Comment thread thrust/testing/transform_scan.cu Resolved

use thrust::placeholders

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bernhardmgruber approved these changes Nov 19, 2025

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dkolsen-pgi reviewed Nov 19, 2025

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remove unnecessary check

0b1e611

bernhardmgruber approved these changes Nov 20, 2025

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bernhardmgruber enabled auto-merge (squash) November 20, 2025 00:05

dkolsen-pgi approved these changes Nov 20, 2025

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github-project-automation Bot moved this from In Progress to In Review in CCCL Nov 20, 2025

bernhardmgruber merged commit bb8a5b9 into NVIDIA:main Nov 20, 2025
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github-project-automation Bot moved this from In Review to Done in CCCL Nov 20, 2025

github-actions Bot pushed a commit that referenced this pull request Nov 20, 2025

fix omp scan bug (#6560)

86c41db

Co-authored-by: Bernhard Manfred Gruber <bernhardmgruber@gmail.com> (cherry picked from commit bb8a5b9)

github-actions Bot mentioned this pull request Nov 20, 2025

[Backport branch/3.2.x] fix omp scan bug #6704

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🥳 CI Workflow Results

🟩 Finished in 1h 30m: Pass: 100%/84 | Total: 14h 28m | Max: 42m 40s | Hits: 88%/116157

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