[cudax] Expose implict_hierarchy[_1d]

[davebayer]

This PR makes the implicit_hierarchy public and adds the implicit_hierarchy_1d function for generating dynamic 1D hierarchy. This will be useful for users that don't use cuda::launch to use the groups and need to construct the hierarchy themselves on device.

I've also removed the default constructor from this_meow groups. User should be aware he is using the dynamic hierarchy and use implicit_hierarchy_1d whenever possible to optimize the queries.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added support for creating implicit one-dimensional hierarchies with dynamic grid, cluster, and block extents.
  • Added a public hierarchy construction helper for multidimensional configurations.
  • Cooperative group types now initialize from an explicitly supplied hierarchy.

• Improvements

  • Group construction provides clearer, more predictable hierarchy configuration.
  • One-dimensional and multidimensional launch configurations are supported and validated consistently.

• Tests

  • Added coverage for hierarchy dimensions, return behavior, error guarantees, and supported launch configurations.

Walkthrough

Changes

The change adds implicit_hierarchy_1d() with dynamic one-dimensional extents, renames __implicit_hierarchy(), updates Cooperative Groups construction, and adds CUDA coverage for hierarchy types, extents, and launches.

Implicit hierarchy support

Layer / File(s)	Summary
Hierarchy contracts and helpers cudax/include/cuda/experimental/__group/fwd.cuh, cudax/include/cuda/experimental/__group/implicit_hierarchy.cuh	Adds __implicit_hierarchy_1d_t, renames __implicit_hierarchy() to implicit_hierarchy(), and adds implicit_hierarchy_1d() with dynamic first-axis extents.
Group construction wiring cudax/include/cuda/experimental/__group/this_group.cuh, cudax/test/coop/any_of/*.cu, cudax/test/group/make_this_group.cu, cudax/test/group/this_group.cu	Removes implicit base construction. Cooperative Groups constructors now initialize with implicit_hierarchy(). Tests use explicit hierarchy configurations.
Hierarchy API validation cudax/test/CMakeLists.txt, cudax/test/group/implicit_hierarchy.cu	Registers tests for return types, noexcept, runtime extents, one-dimensional and multidimensional launches, and supported cluster configurations.

Suggested reviewers: andralex

Merge Risk: ⚪ Minimal · up to 194d6

The PR exposes the hierarchy APIs and removes default construction for these groups; the remaining concerns are limited to test assertions, headers, naming, and const-correctness. No actionable merge-blocking risk remains after normal checks and review.

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (3)

cudax/include/cuda/experimental/__group/implicit_hierarchy.cuh (2)

25-26: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

suggestion: Remove the unused span forward-declaration header. This file does not use span.

As per coding guidelines, “Remove unneeded headers.” As per path instructions, cudax/** changes apply CCCL common style guidance.

Sources: Coding guidelines, Path instructions

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55-55: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

suggestion: Use snake_case for both local type aliases.

• cudax/include/cuda/experimental/__group/implicit_hierarchy.cuh#L55-L55: Rename _Exts1D to a snake_case alias.
• cudax/test/group/make_this_group.cu#L26-L26: Rename Hierarchy to hierarchy_type.

As per coding guidelines, “Use snake_case for all other symbols, except that the CUB public API uses PascalCase.”

Source: Coding guidelines

cudax/test/group/this_group.cu (1)

275-283: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

suggestion: Declare the test-only group values const.

• cudax/test/group/this_group.cu#L275-L283: Change test_common_properties to accept const Group&, then declare group as const.
• cudax/test/group/make_this_group.cu#L31-L32: Declare group as const; sync() is const and no mutation occurs.

As per coding guidelines, “All variables that are not modified must be declared const.”

Source: Coding guidelines

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📥 Commits

Reviewing files that changed from the base of the PR and between 0619e15 and 194d633.

📒 Files selected for processing (9)

• cudax/include/cuda/experimental/__group/fwd.cuh
• cudax/include/cuda/experimental/__group/implicit_hierarchy.cuh
• cudax/include/cuda/experimental/__group/this_group.cuh
• cudax/test/CMakeLists.txt
• cudax/test/coop/any_of/this_thread.cu
• cudax/test/coop/any_of/this_warp.cu
• cudax/test/group/implicit_hierarchy.cu
• cudax/test/group/make_this_group.cu
• cudax/test/group/this_group.cu

Included review availability: Your plan provides up to 12 included reviews per hour; 10 remain after this review.

[miscco]

Should this also test implicit_hierarchy_1d?

[davebayer]

I don't think so to be honest. We will change these tests anyway sooner or later

[github-actions]

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