[mlir][Tensor] Fold destination-style ops into tensor.unpack operation.

The destination operand of the `tensor.unpack` operation is only
needed to carry shape information. So if the producer of the
destination operand implements the `DestinationStyleOpInterface`, then
fold it into the `tensor.unpack` operation by replacing the
destination operand with the destination for the source.

Author: MaheshRavishankar

mlir/lib/Dialect/Tensor/IR/TensorOps.cpp

@@ -3925,15 +3925,25 @@ UnPackOp UnPackOp::createTransposedClone(OpBuilder &b, Location loc,
 /// pack(unpack(x)) -> x
 LogicalResult UnPackOp::canonicalize(UnPackOp unPackOp,
                                      PatternRewriter &rewriter) {
-  PackOp packOp = unPackOp.getSource().getDefiningOp<tensor::PackOp>();
-  if (!packOp || packOp.getDestType() != unPackOp.getSourceType())
-    return failure();
-  if (packOp.getPaddingValue() ||
-      !hasSameInnerOuterAttribute(packOp, unPackOp) ||
-      !haveSameTiles(packOp, unPackOp))
-    return failure();
-  rewriter.replaceOp(unPackOp, packOp.getSource());
-  return success();
+  if (PackOp packOp = unPackOp.getSource().getDefiningOp<tensor::PackOp>()) {
+    if (packOp.getDestType() != unPackOp.getSourceType())
+      return failure();
+    if (packOp.getPaddingValue() ||
+        !hasSameInnerOuterAttribute(packOp, unPackOp) ||
+        !haveSameTiles(packOp, unPackOp))
+      return failure();
+    rewriter.replaceOp(unPackOp, packOp.getSource());
+    return success();
+  }
+  if (DestinationStyleOpInterface dstStyleOp =
+          unPackOp.getDest().getDefiningOp<DestinationStyleOpInterface>()) {
+    OpResult destValue = unPackOp.getDest().cast<OpResult>();
+    Value newDest = dstStyleOp.getDpsInits()[destValue.getResultNumber()];
+    rewriter.updateRootInPlace(
+        unPackOp, [&]() { unPackOp.setDpsInitOperand(0, newDest); });
+    return success();
+  }
+  return failure();
 }
 
 bool UnPackOp::isLikeUnPad() {

mlir/test/Dialect/Tensor/canonicalize.mlir

@@ -1861,3 +1861,19 @@ func.func @invalid_empty_negative_size() -> (tensor<4x5x?xf32>) {
   %1 = tensor.empty(%0) : tensor<4x5x?xf32>
   return %1 : tensor<4x5x?xf32>
 }
+
+// -----
+
+// Fold DstStyleOp -> tensor.unpack operations.
+func.func @fold_dst_style_ops_into_unpack(%arg0 : tensor<?x?x16x64xf32>, %init : tensor<?x?xf32>) -> tensor<?x?xf32> {
+  %cst = arith.constant 0.0 : f32
+  %fill = linalg.fill ins(%cst : f32) outs(%init : tensor<?x?xf32>) -> tensor<?x?xf32>
+  %unpack = tensor.unpack %arg0 inner_dims_pos = [0, 1] inner_tiles = [16, 64] into %fill : tensor<?x?x16x64xf32> -> tensor<?x?xf32>
+  return %unpack : tensor<?x?xf32>
+}
+// CHECK-LABEL: func @fold_dst_style_ops_into_unpack
+//  CHECK-SAME:     %[[ARG0:.+]]: tensor<?x?x16x64xf32>
+//  CHECK-SAME:     %[[ARG1:.+]]: tensor<?x?xf32>
+//       CHECK:   %[[UNPACK:.+]] = tensor.unpack %[[ARG0]]
+//  CHECK-SAME:       into %[[ARG1]]
+//       CHECK:   return %[[UNPACK]]