b10730

qwen4exp: sum the indexer heads by slices (#28023)

• qwen4exp: sum the indexer heads by slices

The head reduction went through a transpose and a sum_rows over ne[1],
which left sum_rows with ne0 = 4, one block per row for a four element
reduction, and the transpose copied the whole block by token surface
twice on the way in.

The heads are adjacent on ne[1], so each one is a strided view and the
sum is a short chain of adds.

RTX PRO 6000, Qwen3.8-Flash-Next UD-Q4_K_XL, fa on, 55k context, warm
runs on top of #28011:

prompt processing 2170 -> 2366 t/s

Generation is unaffected. The removed work scales with n_blocks by
n_tokens, so the gain grows with context and with ubatch size.

• qwen4exp: drop the redundant cont on the indexer query

rope returns a freshly allocated, contiguous tensor, so the reshape that
feeds the matmul does not need a copy. ggml_reshape_3d asserts
contiguity, so a layout that would need the cont cannot slip through
silently.

Greedy output is unchanged token for token.

Address review from @ggerganov

Website:

• https://llama.app

Attestations:

• https://github.com/ggml-org/llama.cpp/attestations/44321551

macOS/iOS:

• macOS Apple Silicon (arm64)
• macOS Apple Silicon (arm64, KleidiAI enabled) DISABLED
• macOS Intel (x64)
• iOS XCFramework

Linux:

• Ubuntu x64 (CPU)
• Ubuntu arm64 (CPU)
• Ubuntu s390x (CPU)
• Ubuntu x64 (Vulkan)
• Ubuntu arm64 (Vulkan)
• Ubuntu x64 (ROCm 7.14)
• Ubuntu x64 (OpenVINO)
• Ubuntu x64 (SYCL FP32)
• Ubuntu x64 (SYCL FP16)

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• Windows arm64 (OpenCL Adreno)
• Windows x64 (CUDA 12) - CUDA 12.4 DLLs
• Windows x64 (CUDA 13) - CUDA 13.3 DLLs
• Windows arm64 (CUDA 13) (preview) - CUDA 13.4 DLLs
• Windows x64 (Vulkan)
• Windows x64 (OpenVINO)
• Windows x64 (SYCL)
• Windows x64 (ROCm 7.14)

openEuler:

• DISABLED
• openEuler x86 (310p)
• openEuler x86 (910b, ACL Graph)
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• openEuler aarch64 (910b, ACL Graph)

UI:

• UI