The CPU `set_rows` kernel for F32 sources fetches `type_traits[dst->type].from_float`
and calls it for every scattered row. F32 has no `from_float` entry, it is NULL in
`type_traits`, so any `set_rows` into an F32 destination calls a NULL function pointer
and segfaults. Other destination types work because they all have a real `from_float`.
Repro (CPU backend, standalone ggml graph):
dst = new_tensor_2d(F32, 8, 6) // F32 destination
src = new_tensor_2d(F32, 8, 4)
idx = new_tensor_1d(I64, 4) // {0,2,4,5}
out = ggml_set_rows(dst, src, idx)
// ggml_backend_graph_compute(cpu, ...) -> SIGSEGV on current main
When the destination is F32, copy the row with `memcpy` instead of going through
`from_float`. The I32 and I64 index branches both get the same treatment. An assert
guards the remaining case, non-F32 dst with a NULL `from_float`, so a future
unsupported type fails loudly instead of crashing.
I ran a normal model after this and it still decodes fine (DeepSeek-V2-Lite-Q4_K_M,
CPU, coherent output), and the non-F32 path is untouched. On the F32 path you pay one
`memcpy` per row in place of the indirect call.
Co-authored-by: local-llm <local-llm@local-llm-R740.cruvis.org>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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