[mlir][vector] Add pattern to rewrite contiguous ExtractStridedSlice into Extract (#111541)

Co-authored-by: Jakub Kuderski <kubakuderski@gmail.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp b/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp
index ec2ef3fc7501..c2da9347aadc 100644
--- a/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp
+++ b/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp
@@ -329,12 +329,70 @@ public:
   }
 };
 
+/// Pattern to rewrite simple cases of N-D extract_strided_slice, where the
+/// slice is contiguous, into extract and shape_cast.
+class ContiguousExtractStridedSliceToExtract final
+    : public OpRewritePattern<ExtractStridedSliceOp> {
+public:
+  using OpRewritePattern::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(ExtractStridedSliceOp op,
+                                PatternRewriter &rewriter) const override {
+    if (op.hasNonUnitStrides()) {
+      return failure();
+    }
+    Value source = op.getOperand();
+    auto sourceType = cast<VectorType>(source.getType());
+    if (sourceType.isScalable()) {
+      return failure();
+    }
+
+    // Compute the number of offsets to pass to ExtractOp::build. That is the
+    // difference between the source rank and the desired slice rank. We walk
+    // the dimensions from innermost out, and stop when the next slice dimension
+    // is not full-size.
+    SmallVector<int64_t> sizes = getI64SubArray(op.getSizes());
+    int numOffsets;
+    for (numOffsets = sourceType.getRank(); numOffsets > 0; --numOffsets) {
+      if (sizes[numOffsets - 1] != sourceType.getDimSize(numOffsets - 1)) {
+        break;
+      }
+    }
+
+    // If not even the inner-most dimension is full-size, this op can't be
+    // rewritten as an ExtractOp.
+    if (numOffsets == sourceType.getRank()) {
+      return failure();
+    }
+
+    // Avoid generating slices that have unit outer dimensions. The shape_cast
+    // op that we create below would take bad generic fallback patterns
+    // (ShapeCastOpRewritePattern).
+    while (sizes[numOffsets] == 1 && numOffsets < sourceType.getRank() - 1) {
+      ++numOffsets;
+    }
+
+    SmallVector<int64_t> offsets = getI64SubArray(op.getOffsets());
+    auto extractOffsets = ArrayRef(offsets).take_front(numOffsets);
+    Value extract = rewriter.create<vector::ExtractOp>(op->getLoc(), source,
+                                                       extractOffsets);
+    rewriter.replaceOpWithNewOp<vector::ShapeCastOp>(op, op.getType(), extract);
+    return success();
+  }
+};
+
 void vector::populateVectorInsertExtractStridedSliceDecompositionPatterns(
     RewritePatternSet &patterns, PatternBenefit benefit) {
   patterns.add<DecomposeDifferentRankInsertStridedSlice,
                DecomposeNDExtractStridedSlice>(patterns.getContext(), benefit);
 }
 
+void vector::populateVectorContiguousExtractStridedSliceToExtractPatterns(
+    RewritePatternSet &patterns, PatternBenefit benefit) {
+  patterns.add<ContiguousExtractStridedSliceToExtract>(patterns.getContext(),
+                                                       benefit);
+}
+
 void vector::populateVectorExtractStridedSliceToExtractInsertChainPatterns(
     RewritePatternSet &patterns,
     std::function<bool(ExtractStridedSliceOp)> controlFn,