metal : clamp K extent in tensor API mat-mat kernel for K not a multiple of 32 (#27450)
The Tensor API mat-mat path of kernel_mul_mm (GGML_METAL_HAS_TENSOR) fed a
static K=32 tile to the matmul2d op on every iteration. On the last, partial
K tile (ne00 % 32 != 0) the src1 slice extends past the K extent of the
tensor, and the op reads those out-of-bounds elements (undefined behavior per
the MSL specification, section 2.22.2). Depending on stale memory contents,
this corrupted the result or produced NaN.
Make the matmul2d op use dynamic_extent for K, and clamp the K extent of both
operand tensor views to the remaining valid K range (min(32, K - loop_k)) per
iteration, so the op reads exactly the valid K range on every iteration
(mirroring the tail handling of the MPP matmul2d examples). On K-aligned
inputs the clamp degenerates to the full 32-wide tile: the only difference
from the static-K op is that the dynamic-K op derives K from the operand
extents and edge-checks the tile against the tensor extents (a handful of
integer ops per iteration).
Add test-backend-ops MUL_MAT cases with K not a multiple of 32 to exercise
the unaligned K path.
Assisted-by: pi:llama.cpp/Qwen3.8-27B
llama.cpp
a3027337 - metal : clamp K extent in tensor API mat-mat kernel for K not a multiple of 32 (#27450)
