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[mlir][Vector] Support scalar vector.extract in VectorLinearize #147440

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Jul 11, 2025
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[mlir][Vector] Support scalar vector.extract in VectorLinearize #147440

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[mlir][Vector] Support scalar `vector.extract` in VectorLinearize
dcaballe Jul 8, 2025
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dcaballe Jul 11, 2025
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54 changes: 39 additions & 15 deletions mlir/lib/Dialect/Vector/Transforms/VectorLinearize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -395,15 +395,32 @@ struct LinearizeVectorShuffle final
}
};

/// This pattern converts the ExtractOp to a ShuffleOp that works on a
/// linearized vector.
/// Following,
/// vector.extract %source [ position ]
/// is converted to :
/// %source_1d = vector.shape_cast %source
/// %out_1d = vector.shuffle %source_1d, %source_1d [ shuffle_indices_1d ]
/// %out_nd = vector.shape_cast %out_1d
/// `shuffle_indices_1d` is computed using the position of the original extract.
/// This pattern linearizes `vector.extract` operations. It generates a 1-D
/// version of the `vector.extract` operation when extracting a scalar from a
/// vector. It generates a 1-D `vector.shuffle` operation when extracting a
/// subvector from a larger vector.
///
/// Example #1:
///
/// %0 = vector.extract %arg0[1]: vector<8x2xf32> from vector<2x8x2xf32>
///
/// is converted to:
///
/// %0 = vector.shape_cast %arg0 : vector<2x8x2xf32> to vector<32xf32>
/// %1 = vector.shuffle %0, %0 [16, 17, 18, 19, 20, 21, 22, 23,
/// 24, 25, 26, 27, 28, 29, 30, 31] :
/// vector<32xf32>, vector<32xf32>
/// %2 = vector.shape_cast %1 : vector<16xf32> to vector<8x2xf32>
///
/// Example #2:
///
/// %0 = vector.extract %arg0[1, 2] : i32 from vector<2x4xi32>
///
/// is converted to:
///
/// %0 = vector.shape_cast %arg0 : vector<2x4xi32> to vector<8xi32>
/// %1 = vector.extract %0[6] : i32 from vector<8xi32>
///
struct LinearizeVectorExtract final
: public OpConversionPattern<vector::ExtractOp> {
using OpConversionPattern::OpConversionPattern;
Expand All @@ -413,10 +430,6 @@ struct LinearizeVectorExtract final
LogicalResult
matchAndRewrite(vector::ExtractOp extractOp, OpAdaptor adaptor,
ConversionPatternRewriter &rewriter) const override {
// Skip if result is not a vector type
if (!isa<VectorType>(extractOp.getType()))
return rewriter.notifyMatchFailure(extractOp,
"scalar extract not supported");
Type dstTy = getTypeConverter()->convertType(extractOp.getType());
assert(dstTy && "expected 1-D vector type");

Expand All @@ -436,10 +449,21 @@ struct LinearizeVectorExtract final
linearizedOffset += offsets[i] * size;
}

Value srcVector = adaptor.getVector();
if (!isa<VectorType>(extractOp.getType())) {
// Scalar case: generate a 1-D extract.
Value result = rewriter.createOrFold<vector::ExtractOp>(
extractOp.getLoc(), srcVector, linearizedOffset);
rewriter.replaceOp(extractOp, result);
return success();
}

// Vector case: generate a shuffle.

llvm::SmallVector<int64_t, 2> indices(size);
std::iota(indices.begin(), indices.end(), linearizedOffset);
rewriter.replaceOpWithNewOp<vector::ShuffleOp>(
extractOp, dstTy, adaptor.getVector(), adaptor.getVector(), indices);
rewriter.replaceOpWithNewOp<vector::ShuffleOp>(extractOp, dstTy, srcVector,
srcVector, indices);

return success();
}
Expand Down
26 changes: 13 additions & 13 deletions mlir/test/Dialect/Vector/linearize.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -264,6 +264,19 @@ func.func @test_vector_shuffle(%arg0: vector<4x2xf32>, %arg1: vector<4x2xf32>) -

// -----

// CHECK-LABEL: test_vector_extract_scalar
// CHECK-SAME: (%[[ARG:.*]]: vector<2x4xi32>) -> i32 {
func.func @test_vector_extract_scalar(%arg0 : vector<2x4xi32>) -> i32 {

// CHECK: %[[SRC_1D:.*]] = vector.shape_cast %[[ARG]] : vector<2x4xi32> to vector<8xi32>
// CHECK: %[[EXTRACT_1D:.*]] = vector.extract %[[SRC_1D]][6] : i32 from vector<8xi32>
// CHECK: return %[[EXTRACT_1D]] : i32
%0 = vector.extract %arg0[1, 2] : i32 from vector<2x4xi32>
return %0 : i32
}

// -----

// CHECK-LABEL: test_vector_extract
// CHECK-SAME: (%[[ORIG_ARG:.*]]: vector<2x8x2xf32>) -> vector<8x2xf32> {
func.func @test_vector_extract(%arg0: vector<2x8x2xf32>) -> vector<8x2xf32> {
Expand Down Expand Up @@ -341,19 +354,6 @@ func.func @test_vector_insert_scalable(%arg0: vector<2x8x[4]xf32>, %arg1: vector

// -----

// CHECK-LABEL: test_vector_extract_scalar
func.func @test_vector_extract_scalar(%idx : index) {
%cst = arith.constant dense<[1, 2, 3, 4]> : vector<4xi32>

// CHECK-NOT: vector.shuffle
// CHECK: vector.extract
// CHECK-NOT: vector.shuffle
%0 = vector.extract %cst[%idx] : i32 from vector<4xi32>
return
}

// -----

// CHECK-LABEL: test_vector_bitcast
// CHECK-SAME: %[[ARG_0:.*]]: vector<4x4xf32>
func.func @test_vector_bitcast(%arg0: vector<4x4xf32>) -> vector<4x8xf16> {
Expand Down
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