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[mlir][tensor] Preserve encoding when folding empty #176427

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sommerlukas merged 3 commits into from
Jan 19, 2026
Merged

[mlir][tensor] Preserve encoding when folding empty #176427

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[mlir][tensor] Preserve encoding when folding empty
sommerlukas Jan 16, 2026
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sommerlukas Jan 16, 2026
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sommerlukas Jan 19, 2026
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7 changes: 5 additions & 2 deletions mlir/lib/Dialect/Tensor/Transforms/EmptyOpPatterns.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,11 +40,14 @@ struct FoldEmptyTensorWithReshapeOp : public OpRewritePattern<ReshapeOp> {
!llvm::hasSingleElement(resultShapes))
return failure();

Attribute encoding;
if (auto tensorTy = dyn_cast<RankedTensorType>(reshapeOp.getResultType()))
encoding = tensorTy.getEncoding();

// Create new tensor.empty op.
// TODO: Do not drop tensor type encoding.
Value emptyTensor =
EmptyOp::create(rewriter, loc, resultShapes[0],
reshapeOp.getResultType().getElementType());
reshapeOp.getResultType().getElementType(), encoding);
if (emptyTensor.getType() != reshapeOp.getResultType()) {
rewriter.replaceOpWithNewOp<tensor::CastOp>(
reshapeOp, reshapeOp.getResultType(), emptyTensor);
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21 changes: 21 additions & 0 deletions mlir/test/Dialect/Tensor/fold-empty-op.mlir
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Expand Up @@ -37,6 +37,27 @@ func.func @empty_reshape_collapse(%arg0 : index) -> tensor<6x5x?xf32> {
// CHECK-NEXT: %[[INIT:.+]] = tensor.empty(%[[D]])
// CHECK-NEXT: return %[[INIT]]

#encoding = #test.tensor_encoding<"encoding">

func.func @empty_expand_encoding() -> tensor<2x3x4x2xf32, #encoding> {
%0 = tensor.empty() : tensor<6x8xf32, #encoding>
%1 = tensor.expand_shape %0 [[0, 1], [2, 3]] output_shape [2, 3, 4, 2] : tensor<6x8xf32, #encoding> into tensor<2x3x4x2xf32, #encoding>
return %1 : tensor<2x3x4x2xf32, #encoding>
}
// CHECK-LABEL: func.func @empty_expand_encoding
// CHECK: %[[INIT:.+]] = tensor.empty() : tensor<2x3x4x2xf32, #test.tensor_encoding<"encoding">>
// CHECK-NEXT: return %[[INIT]]

func.func @empty_collapse_encoding() -> tensor<6x8xf32, #encoding> {
%0 = tensor.empty() : tensor<2x3x4x2xf32, #encoding>
%1 = tensor.collapse_shape %0 [[0, 1], [2, 3]]
: tensor<2x3x4x2xf32, #encoding> into tensor<6x8xf32, #encoding>
return %1 : tensor<6x8xf32, #encoding>
}
// CHECK-LABEL: func.func @empty_collapse_encoding
// CHECK: %[[EMPTY_0:.*]] = tensor.empty() : tensor<6x8xf32, #test.tensor_encoding<"encoding">>
// CHECK-NEXT: return %[[EMPTY_0]]

func.func @fold_empty_tensor_with_slice
(%arg0 : index, %arg1 : index) -> tensor<5x?x20xf32>
{
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