At the moment, `GenericPadOpVectorizationPattern` implements two
orthogonal transformations:
1. Rewrites `tensor::PadOp` into a sequence of `tensor::EmptyOp`,
`linalg::FillOp` and `tensor::InsertSliceOp`.
2. Vectorizes (where possible) `tensor::InsertSliceOp` (see
`tryVectorizeCopy`).
This patch splits `GenericPadOpVectorizationPattern` into two separate
patterns:
1. `GeneralizePadOpPattern` for the first transformation (note that
currently `GenericPadOpVectorizationPattern` inherits from
`GeneralizePadOpPattern`).
2. `InsertSliceVectorizePattern` to vectorize `tensor::InsertSliceOp`.
With this change, we gain the following:
* a clear separation between pre-processing and vectorization
transformations/stages,
* a path to support masked vectorisation for `tensor.insert_slice`
(with a dedicated pattern for vectorization, it is much easier to
specify the input vector sizes used in masking),
* more opportunities to vectorize `tensor.insert_slice`.
Note for downstream users:
--------------------------
If you were using `populatePadOpVectorizationPatterns`, following this
change you will also have to add
`populateInsertSliceVectorizationPatterns`.
Finer implementation details:
-----------------------------
1. The majority of changes in this patch are copy & paste + some edits.
1.1. The only functional change is that the vectorization of
`tensor.insert_slice` is now broadly available (as opposed to being
constrained to the pad vectorization pattern:
`GenericPadOpVectorizationPattern`).
1.2. Following-on from the above, `@pad_and_insert_slice_dest` is
updated. As expected, the input `tensor.insert_slice` Op is no
longer "preserved" and instead gets vectorized successfully.
2. The `linalg.fill` case in `getConstantPadVal` works under the
assumption that only _scalar_ source values can be used. That's
consistent with the definition of the Op, but it's not tested at the
moment. Hence a test case in Linalg/invalid.mlir is added.
3. The behaviour of the two TD vectorization Ops,
`transform.structured.vectorize_children_and_apply_patterns` and
`transform.structured.vectorize` is preserved.
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