[Mlir-commits] [mlir] [mlir][linalg] Enable scalable vectorization of linalg.unpack (PR #149293)

[Han-Chung Wang]

================
@@ -1831,126 +1832,138 @@ vectorizeAsTensorPackOp(RewriterBase &rewriter, linalg::PackOp packOp,
   return success();
 }
 
-/// Vectorize a `linalg::UnPackOp` to these 4 Ops:
-///   Vector::TransferReadOp - Reads a vector from the source tensor
-///   vector::TransposeOp - Transpose the Source tensor
-///   ShapeCastOp - Reshape the data based on the target.
-///   vector::TransferWriteOp. - Write the result vector back to the destination
-///   tensor.
-///   If the vector sizes are not provided:
-///   * the vector sizes are determined by the input operand and attributes,
-///   * update the inBounds attribute instead of masking.
+/// Vectorize `linalg.unpack` into:
+///   * xfer_read -> vector.transpose -> vector.shape_cast -> xfer_write
+///
+/// The input-vector-sizes specify both the read and the write vector
+/// sizes and are passed as one array covering both operations, i.e.:
+///
+///  input-vector-sizes = [1, 1, 8, [8],  8, [8]]
+///                        \         /    \    /
+///                        read-sizes   write-sizes
+///
+/// (for brefity, in the diagram,
+///    * input-vector-sizes = `inputVectorSizes` + `inputScalableDims`
+/// )
+///
+/// If the vector sizes are not provided:
+///  * the vector sizes are determined by the operands,
+///  * the inBounds attribute is used instead of masking.
+///
+/// EXAMPLE (no vector sizes):
+/// ```
+///   %unpack = linalg.unpack  %src
+///    inner_dims_pos = [0, 1]
+///    inner_tiles = [8, 8]
+///    into %dest : tensor<1x1x8x8xf32> -> tensor<8x8xf32>
+/// ```
+/// is vectorized as:
+/// ```
+///   // Reads a vector from the source tensor
+///   %read = vector.transfer_read  %src
+///     : tensor<1x1x8x8xf32>, vector<1x1x8x8xf32>
+///   // Transpose %read as specified in `outer_dims_perm` attribute
+///   %tr = vector.transpose %read [0, 2, 1, 3]
+///     : vector<1x1x8x8xf32> to vector<1x8x1x8xf32>
+///   // Reshape the data based on the target
+///   %sc = vector.shape_cast %tr : vector<1x8x1x8xf32> to vector<8x8xf32>
+///   // Write the result vector to the destination tensor.
+///   vector.transfer_write %sc into %dest : vector<8x8xf32>, tensor<8x8xf32>
----------------
hanhanW wrote:

optional nit: technically, it has a return value.
```suggestion
///   %write = vector.transfer_write %sc into %dest
        : vector<8x8xf32>, tensor<8x8xf32>
```

https://github.com/llvm/llvm-project/pull/149293