Make tensor*tensor implementation easier to read. #16839
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Part of #16465 . |
| reordered = TensorAccessors::reordered_index_view<0, rank_2>(src2); | ||
| TensorAccessors::contract<1, rank_1, rank_2, dim>(result, | ||
| src1, | ||
| reordered); |
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It took me considerable effort to come up with one generic implementation instead of special casing contractions of different template parameters fortran style.
And I fear right now that you are undoing a lot of this work.
Despite the rather intimidating template magic - the entire tensor contraction logic boils down to one loop where we do this:
for (unsigned int i = 0; i < dim; ++i)
result[i] += src1[i] * src2;
So, why not adding the vectorization bits there?
Relatedly, we could also ditch the Reordered IndexView for the special case of a "last and first index" contraction and provide a specialized, vectorized recursive template for that one.
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Of course that's the plan. I needed to create a place where I can put the vectorization in the next patch. This patch creates this place. It also, perhaps, makes the compiler's life easier for the two simplest cases.
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Separately, though: I'm not ditching the generic implementation. There remain the various contract() functions that I don't intend to touch. They're the main users of your general approach, which I continue to admire. I just think that in these two specific cases, things are so simple that we can perhaps allow us to just write the obvious code :-)
In particular, treat the two most common cases separately and perhaps gain a bit of efficiency that way if that helps compilers.