[Ziminli]

This PR keeps the high-level build flow visible in the root CMakeLists.txt while moving platform- and backend-specific detection and dependency setup into focused modules under cmake/devices and cmake/backends.

This PR also standardizes device auto-detection so a device explicitly enabled with WITH_*=ON remains enabled while auto-detection adds other detected devices.

No runtime API, collective algorithm, or intended platform behavior changes.

Changes

• Central CMake Orchestration

  • Keep the option declarations, device/backend detection order, cross-device policy, and dependency configuration sequence in the root CMakeLists.txt.
  • Replace platform-specific implementation blocks with named detection, probe, and configuration calls.

• Device-specific Modules

  • Add modules for NVIDIA, Iluvatar, MetaX, Moore Threads, Cambricon, HYGON, and T-Head detection and SDK configuration.
  • Move vendor-specific path hints, compiler selection, runtime library lookup, and T-Head CUDA-compatible toolkit resolution into their owning modules.
  • Add infiniccl_resolve_device_detection to preserve explicit WITH_*=ON selections and probe only devices that were not explicitly requested.

• Backend-specific Modules

  • Add modules for MPI, NCCL/RCCL, MCCL, and CNCL detection and required dependency resolution.
  • Keep vendor-specific NCCL/RCCL and MCCL hints local to the relevant backend/device paths.

• Behavior Preservation and Documentation

  • Add an explicit return to the HYGON-compiled PrintResult helper in examples/ccl/reduce_scatter.cc to avoid the compiler's missing-return warning.
  • Document that auto-detection is additive to explicit device/backend selections and that users can disable auto-detection for a strictly manual configuration.

Platform and Backend Affected

Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU
• T-Head PPU

Backend

• OpenMPI
• MPICH
• NCCL/RCCL
• MCCL
• CNCL

Performance Impact

• No performance impact
• Performance improved
• Performance regression possible

N/A. This PR reorganizes configure-time discovery and preserves existing build behavior; it does not change runtime communication paths or collective algorithms.

Known Issues & Future Work

• N/A.

Test Results

Test Involved Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU
• T-Head PPU

Test Involved Backend

• OpenMPI
• MPICH
• NCCL/RCCL
• MCCL
• CNCL

NVIDIA+MetaX+Moore with OMPI:
mpi_all_gather.log
mpi_all_reduce.log
mpi_all_to_all.log
mpi_broadcast.log
mpi_gather.log
mpi_reduce.log
mpi_reduce_scatter.log
mpi_scatter.log
mpi_send_recv.log

Iluvatar with NCCL:
ccl_all_gather.log
ccl_all_reduce.log
ccl_reduce_scatter.log
ccl_send_recv.log

HYGON with RCCL+OMPI:
ccl_mpi_hybrid_all_gather.log
ccl_mpi_hybrid_all_reduce.log
ccl_mpi_hybrid_send_recv.log

T-Head with NCCL:
ccl_all_gather.log
ccl_all_reduce.log
ccl_reduce_scatter.log
ccl_send_recv.log

Cambricon with CNCL:
ccl_mpi_hybrid_all_gather.log
ccl_mpi_hybrid_all_reduce.log
ccl_mpi_hybrid_send_recv.log

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Checklist

Every contributor must verify every item below before requesting
review. Tick each box only after the check has actually been performed —
do not tick speculatively. If an item truly does not apply, replace the
checkbox with N/A and briefly explain why in an inline comment.

Title, Branch, and Commits

• PR title follows Conventional Commits (e.g. feat: …, fix(nccl): …).
• Branch name follows <type>/xxx-yyyy-zzzz where <type> matches the PR title's Conventional Commits type and words are joined with hyphens (see CONTRIBUTING.md §Branches).
• Each commit message follows Conventional Commits.
• Small PR is a single squashable commit; or, for a large PR, every commit is meaningful, well-formed, and independently reviewable (see CONTRIBUTING.md §Pull Requests).
• No stray merge commits from master — the branch is rebased cleanly on top of the current master.
• No fixup! / squash! / wip commits remain.

Scope and Design

• Changes are minimal — no unrelated modifications were introduced (CONTRIBUTING.md §Code/General).
• No dead code, commented-out blocks, debug prints, printf/std::cout/print(...) left behind, or TODO without an owner and issue link.
• No unrelated formatting churn that would obscure the diff.
• N/A- Public API changes (if any) are intentional, documented, and reflected in affected callers/tests.

General Code Hygiene

• The code is self-explanatory; comments were added only where the intent or rationale is non-obvious (CONTRIBUTING.md §Code/General).
• Every modified or added file ends with a single trailing newline (CONTRIBUTING.md §Code/General).
• No trailing whitespace, inconsistent indentation, or mixed formatting styles remain.
• Identifiers referenced in comments or error messages are wrapped in Markdown backticks (e.g. the `AllReduce` implementation) (CONTRIBUTING.md §Code/General).
• All comments and error messages are in English (CONTRIBUTING.md §Code/General).
• Comments and error messages are complete sentences — capitalized first letter, terminal punctuation — unless the language/framework convention says otherwise (CONTRIBUTING.md §Code/General; §Python).

C++ Specific (if C++ files changed)

• Code follows the Google C++ Style Guide strictly.
• clang-format (version 16, per .github/workflows/clang-format.yml) has been run against all modified applicable files; the diff is clean.
• N/A- No exceptions are thrown. Error paths use assert with messages that include at least __FILE__, __LINE__, and __func__ (CONTRIBUTING.md §C++).
• N/A- Error and warning message wording follows the LLVM Coding Standards (CONTRIBUTING.md §C++).
• N/A- Constructor initializer list order matches member declaration order (CONTRIBUTING.md §C++).
• N/A- Exactly one blank line between classes, between classes and functions, and between functions (CONTRIBUTING.md §C++).
• N/A- Exactly one blank line between members (functions and variables) within a class (CONTRIBUTING.md §C++).
• N/A- Exactly one blank line before and after the contents of a namespace (CONTRIBUTING.md §C++).

Python Specific (if Python files changed)

• N/A. No Python files were changed.

Testing

• All applicable example programs have been built and tested successfully on at least one supported heterogeneous cluster setup.

Build, CI, and Tooling

• New backends or devices have been added to auto-detection in CMakeLists.txt under if(AUTO_DETECT_DEVICES) or to if(AUTO_DETECT_BACKENDS) if applicable.
• Both CI workflows (clang-format.yml, ruff.yml) are green locally (or expected to be green on CI).

Documentation

• README.md, CONTRIBUTING.md, or inline docs updated when behavior, build flags, or developer workflow changed.
• N/A- Any user-visible breaking change is called out explicitly under "Summary" and in the commit/PR title with a ! or BREAKING CHANGE: footer.

Security and Safety

• No secrets, access tokens, internal URLs, customer data, or personal hardware identifiers have been committed.
• N/A- Third-party code is license-compatible and attributed.
• N/A- No unsafe pointer arithmetic, uninitialized reads, or missing bounds checks were introduced.