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Refactor mdspancuda::std::__detectably_invalid - #6733

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fbusato merged 29 commits into
NVIDIA:mainfrom
fbusato:host-device-mdspan-accessible
Jan 8, 2026
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Refactor mdspancuda::std::__detectably_invalid#6733
fbusato merged 29 commits into
NVIDIA:mainfrom
fbusato:host-device-mdspan-accessible

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@fbusatofbusato commented Nov 22, 2025

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Description

Replace old code in host/device/managed mdspan with https://nvidia.github.io/cccl/libcudacxx/extended_api/memory/is_pointer_accessible.html

@fbusatofbusato self-assigned this Nov 22, 2025
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fbusato requested a review from a team as a code ownerNovember 22, 2025 02:03
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fbusato requested a review from wmaxeyNovember 22, 2025 02:03
@fbusatofbusato changed the title Applies `is_pointer_accessible to mdspanApplies is_pointer_accessible to mdspanNov 22, 2025
@cccl-authenticator-appcccl-authenticator-appBot moved this from Todo to In Review in CCCLNov 22, 2025
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davebayer
davebayer requested changes Nov 22, 2025
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Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h Outdated
Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h Outdated
Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h Outdated
@github-project-automationgithub-project-automationBot moved this from In Review to In Progress in CCCLNov 22, 2025
fbusatoand others added 4 commits November 24, 2025 11:10
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Update libcudacxx/include/cuda/__mdspan/host_device_accessor.h
bd85afb
Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>
@fbusato@davebayer
Update libcudacxx/include/cuda/__mdspan/host_device_accessor.h
46ee442
Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>
@fbusato@davebayer
Update libcudacxx/include/cuda/__mdspan/host_device_accessor.h
a652a74
Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>
@fbusato
use _CCCL_IF_NOT_CONSTEVAL_DEFAULT
b525a76
@fbusatofbusato moved this from In Progress to In Review in CCCLNov 24, 2025
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fbusato commented Nov 24, 2025

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@davebayer@miscco I'm starting thinking that we are doing the wrong thing for host/device/managed.
There are two problems:

  1. We cannot check the pointer validity in respect to the memory space for EVERY access. This involves multiple driver calls. This is too expensive even in debug mode.
  2. We cannot check the device accessibility on the host because its access is always wrong on the host side.

Ideally, mdspan itself should check the pointer during the creating, not during run-time. Two potential solutions:

  • cuda:std::mdpan checks __detectably_invalid.
  • Modify the host/device/managed_mdspan constructs to check the memory space.

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@leofangleofang mentioned this pull request Nov 26, 2025
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davebayer
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Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h Outdated
Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h Outdated
Comment threadlibcudacxx/include/cuda/std/__mdspan/concepts.h Outdated
Comment threadlibcudacxx/include/cuda/std/__mdspan/mdspan.h Outdated
Comment threadlibcudacxx/include/cuda/std/__mdspan/mdspan.h Outdated
Comment threadlibcudacxx/include/cuda/std/__mdspan/mdspan.h Outdated
@github-project-automationgithub-project-automationBot moved this from In Review to In Progress in CCCLDec 8, 2025
fbusatoand others added 2 commits December 8, 2025 12:42
@fbusato@davebayer
Update libcudacxx/include/cuda/__mdspan/host_device_accessor.h
b610ce2
Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>
@fbusato@davebayer
Update libcudacxx/include/cuda/std/__mdspan/concepts.h
87e1a3e
Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>
@fbusatofbusato changed the title Applies is_pointer_accessible to mdspanRefactor cuda::std::__detectably_invalidDec 17, 2025
@fbusatofbusato changed the title Refactor cuda::std::__detectably_invalidRefactor mdspancuda::std::__detectably_invalidDec 18, 2025
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@github-project-automationgithub-project-automationBot moved this from In Progress to In Review in CCCLJan 5, 2026
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miscco
miscco reviewed Jan 6, 2026
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Comment threadlibcudacxx/include/cuda/__mdspan/host_device_accessor.h
Comment threadlibcudacxx/test/libcudacxx/cuda/containers/views/mdspan/device_mdspan/ctor.dh_extents.pass.cpp
// - Direct-non-list-initializes ptr_ with cuda::std::move(p),
// - direct-non-list-initializes map_ with ext, and
// - value-initializes acc_.
#define _CCCL_DISABLE_MDSPAN_ACCESSOR_DETECT_INVALIDITY

@misccomisccoJan 6, 2026

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Why do we need that?

@fbusatofbusatoJan 6, 2026

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it is very hard to reimplement all tests to work with the right accessor respect to the memory space.
I added this macro to disable the checks

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fbusato enabled auto-merge (squash) January 7, 2026 18:00
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github-actionsBot commented Jan 8, 2026

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🥳 CI Workflow Results

🟩 Finished in 2h 10m: Pass: 100%/84 | Total: 1d 12h | Max: 1h 48m | Hits: 86%/197813

See results here.

@fbusato
fbusato merged commit 281f441 into NVIDIA:mainJan 8, 2026
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@github-project-automationgithub-project-automationBot moved this from In Review to Done in CCCLJan 8, 2026
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@bernhardmgruberbernhardmgruberbernhardmgruber approved these changes
@davebayerdavebayerdavebayer approved these changes
@wmaxeywmaxeyAwaiting requested review from wmaxeywmaxey is a code owner automatically assigned from NVIDIA/cccl-libcudacxx-codeowners

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