ggml-org/llama.cpp b11216

on GitHub

sycl: FWHT kernels for block widths above 512 (#29243)

The SYCL FWHT covers 64 to 512 via the standard butterfly network, plus
384/640/768/1280 via the Kronecker/Paley construction added separately in
Hadamard hint can produce (1024, 2048, 4096, 8192); those still fall through
to the default case and run as a dense GEMM against the materialized
rotation tensor, correct but O(n^2) instead of O(n log n).

fwht_kernel_wide runs one row per work-group instead of per sub-group, so
each work-item keeps N/NT values rather than N/WARP_SIZE. Butterflies below
the sub-group width still shuffle; those up to the work-group width go
through work-group local memory; the rest stay in registers. Same butterfly
and sign convention as the existing narrow kernel.

ggml's SYCL backend registration (dpct::dev_mgr) unconditionally requires a
GPU-labeled platform to exist and throws before any op-level test can run,
so test-backend-ops could not be exercised on this box (a GPU-less pod) even
via the CPU device. Verified instead with a standalone harness: the same
kernel body run through a real SYCL CPU device (Intel oneAPI DPC++ 2026.1,
OpenCL CPU backend), checked against an independent recursive-doubling
Hadamard reference, cross-validated by first running the existing unmodified
narrow kernel through the identical harness and confirming it passes (rules
out a reference-convention bug before trusting a pass on the new code).
Random-input results for all four widths, single- and multi-row:

N=1024 NT=256 rows=1 max_abs_err=1.7e-07 max_rel_err=4.9e-04 PASS
N=2048 NT=256 rows=1 max_abs_err=1.9e-07 max_rel_err=2.0e-04 PASS
N=4096 NT=256 rows=1 max_abs_err=2.0e-07 max_rel_err=1.4e-04 PASS
N=8192 NT=256 rows=1 max_abs_err=2.5e-07 max_rel_err=3.8e-03 PASS
N=1024 NT=256 rows=7 max_abs_err=2.4e-07 max_rel_err=1.0e-03 PASS
N=2048 NT=256 rows=5 max_abs_err=3.0e-07 max_rel_err=9.4e-04 PASS
N=4096 NT=256 rows=3 max_abs_err=2.7e-07 max_rel_err=1.7e-03 PASS
N=8192 NT=256 rows=2 max_abs_err=2.5e-07 max_rel_err=1.9e-03 PASS

This covers the kernel algorithm itself; it does not exercise the ggml
dispatch/supports_op integration end to end, which needs a real GPU (or a
SYCL GPU plugin) to get past backend registration. test-backend-ops build
is verified: fwht.cpp recompiles with zero warnings as part of ggml-sycl.