remove one Vec from Tensor - #31
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compute_strides() returned Option<Vec<usize>>, so every Tensor constructor -- from_vec, from_aligned, from_f16, from_bf16, filled, zeros, reshape, into_reshape -- heap-allocated a three-to-five element Vec, had DimsVec::from memcpy it into the inline buffer, and freed it again. DimsVec exists precisely to keep shape and strides off the heap for rank <= 6, so the stride path was paying one malloc/free per tensor to populate a structure designed to avoid exactly that. compute_strides now fills a [usize; INLINE_CAP] and returns the DimsVec directly, keeping the old vec! path only for rank > 6, where DimsVec spills to Heap anyway. The eight call sites move the value into the struct instead of converting it. DimsVec itself is untouched: rank > 6 still works and size_of::<Tensor>() is still 144 bytes. A first attempt that wrote the strides through a DerefMut on DimsVec was slower than the Vec it replaced (37.8 ns/op on the reshape bench) because every index write re-matched the enum discriminant. The win needs the plain array, so keep it that way. Validation: cargo test -p yscv-tensor, 228 passed; scripts/check-ci-local.sh passed. Microbench on a 12th Gen Core i5-12500H, pinned with taskset -c 2, performance governor, min of five interleaved runs against the unpatched binary: reshape of a 4-D tensor 33.6 -> 30.9 ns/op (-8 %), from_vec of a rank-3 tensor 51.0 -> 48.0 ns/op (-6 %), clone unchanged at 13.2 ns/op.
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I really disliked
Vecs out there in tensor, so I inlined strides.Benches: tensor ops -8% avg, onnx bench -3% avg