[nihui]

Create the subgroup reducers and the square/sum4/mean fallback pipelines in mutually exclusive branches, matching LayerNorm. Keep the shared coeffs/norm pipelines unconditional.

This avoids allocating ten unused fallback Pipeline wrappers when the validated subgroup path is enabled.

Follow-up to #6755 and #6755 (comment).

Validation:

• Vulkan-enabled Release build passed.
• Existing test_rmsnorm and test_layernorm passed with SwiftShader (software Vulkan).
• 16 supplementary public-layer Vulkan cases passed with subgroup operations on/off, packing on/off, 1D/3D inputs and affine on/off.
• git diff --check passed.

SwiftShader supports subgroup arithmetic but not fp16 storage/arithmetic, so the existing dedicated fp16a cases were skipped. No hardware startup-time measurements were made.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-18T01:35:02.521238Z	38a2d89	PR opened

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.26%. Comparing base (5d1c5ad) to head (38a2d89).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7133      +/-   ##
==========================================
- Coverage   95.29%   95.26%   -0.03%     
==========================================
  Files        1483     1483              
  Lines      504854   504979     +125     
==========================================
- Hits       481094   481091       -3     
- Misses      23760    23888     +128     

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[github-actions]

Binary size comparison

The binary size change of libncnn.so (bytes)

architecture	base size	pr size	difference
x86_64	27763760	27763760	0 😘
armhf	7723120	7723152	+32 ⚠️
aarch64	11849720	11849720	0 😘

Commit: 38a2d895498d141c3846cb9a0140111b1e4607a1 · Workflow run