[Mlir-commits] [mlir] [MLIR] Add pattern to bubble up tensor.extract_slice (PR #126898)

[Andrzej Warzyński]

================
@@ -210,6 +214,200 @@ struct BubbleUpExpandThroughParallelCollapse
   }
 };
 
+/// Converts `tensor.extract_slice(tensor.expand_shape)` to
+/// `tensor.expand_shape(tensor.extract_slice)`.
+/// For this transformation to be possible, the slice must be fully contiguous
+/// within each reassociation group of the expand_shape. If the transformation
+/// is not possible, or if the slice is rank reducing, the function returns
+/// failure.
+///
+/// Example:
+/// ```
+/// %reshape = tensor.expand_shape %in [[0, 1], [2, 3], [4, 5, 6]]
+///     tensor<8x16x32xf32> to tensor<2x4x2x8x4x2x4xf32>
+/// %slice = tensor.extract_slice %reshape ...
+///     tensor<2x4x2x8x4x2x4xf32> to tensor<2x4x1x5x1x1x4xf32>
+///
+/// // The transformation is possible because each reassociation group has a
+/// // contiguous slice. (i.e., [2x4->2x4], [2x8->1x5], [4x2x4->1x1x4])
+/// // After the transformation:
+///
+/// %slice = tensor.extract_slice %in ...
+///     tensor<8x16x32xf32> to tensor<8x5x4xf32>
+/// %reshape = tensor.expand_shape %slice [[0, 1], [2, 3], [4, 5, 6]]
+///     tensor<8x5x4xf32> to tensor<2x4x1x5x1x1x4xf32>
+/// ```
+///
+/// Note - this pattern could be reworked to be a swap pattern between
+/// `tensor.expand_shape` and `tensor.extract_slice`, but is currently
+/// implemented only as a bubble up pattern for `tensor.extract_slice`.
+struct BubbleUpExpandShapeThroughExtractSlice
+    : public OpRewritePattern<tensor::ExtractSliceOp> {
+  using OpRewritePattern<tensor::ExtractSliceOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(tensor::ExtractSliceOp sliceOp,
+                                PatternRewriter &rewriter) const override {
+    auto expandShapeOp =
+        sliceOp.getSource().getDefiningOp<tensor::ExpandShapeOp>();
+
+    if (checkPreconditionForBubbleUpExtractSlice(sliceOp, expandShapeOp,
+                                                 rewriter)
+            .failed())
+      return failure();
+
+    SmallVector<OpFoldResult> offsets = sliceOp.getMixedOffsets();
+    SmallVector<OpFoldResult> sizes = sliceOp.getMixedSizes();
+    SmallVector<OpFoldResult> outputShape =
+        getMixedValues(expandShapeOp.getStaticOutputShape(),
+                       expandShapeOp.getOutputShape(), rewriter);
+
+    // Helper variables and function for accumulating the new offset and length
+    // values.
+    Location loc = expandShapeOp->getLoc();
+    AffineExpr d0, d1, d2;
+    bindDims(rewriter.getContext(), d0, d1, d2);
+    // Multiply two integers.
+    auto mul = [&](OpFoldResult v1, OpFoldResult v2) {
+      auto mulMap = AffineMap::get(2, 0, {d0 * d1});
+      return affine::makeComposedFoldedAffineApply(rewriter, loc, mulMap,
+                                                   {v1, v2});
+    };
+
+    // Compute new offsets, lengths, and strides.
+    SmallVector<OpFoldResult> newOffsets, newLengths, newStrides;
+    for (const ReassociationIndices &indices :
+         expandShapeOp.getReassociationIndices()) {
+      OpFoldResult newSize = rewriter.getIndexAttr(1);
+      SmallVector<OpFoldResult> basis, delinOffsets;
----------------
banach-space wrote:

Ha, now everything is clear!

[nit]  Reading your comment made me think: `basis` -> `reassocGroupSizes` and `delinOffsets` -> `reassocGroupOffsets`. These are rather mouthful, but then you could skip the comment. But honestly, feel free to ignore if you like the current names :)

https://github.com/llvm/llvm-project/pull/126898