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[mlir][Vector] Lower vector.to_elements to LLVM #145766

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Jun 26, 2025
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[mlir][Vector] Lower vector.to_elements to LLVM #145766

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[mlir][Vector] Add `vector.to_elements` lowering to LLVM
dcaballe Jun 25, 2025
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dcaballe Jun 26, 2025
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35 changes: 34 additions & 1 deletion mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1985,6 +1985,38 @@ struct VectorFromElementsLowering
}
};

/// Conversion pattern for a `vector.to_elements`.
struct VectorToElementsLowering
: public ConvertOpToLLVMPattern<vector::ToElementsOp> {
using ConvertOpToLLVMPattern::ConvertOpToLLVMPattern;

LogicalResult
matchAndRewrite(vector::ToElementsOp toElementsOp, OpAdaptor adaptor,
ConversionPatternRewriter &rewriter) const override {
Location loc = toElementsOp.getLoc();
auto idxType = typeConverter->convertType(rewriter.getIndexType());
Value source = adaptor.getSource();

SmallVector<Value> results(toElementsOp->getNumResults());
for (auto [idx, element] : llvm::enumerate(toElementsOp.getElements())) {
// Create an extractelement operation only for results that are not dead.
if (element.use_empty())
continue;

auto constIdx = rewriter.create<LLVM::ConstantOp>(
loc, idxType, rewriter.getIntegerAttr(idxType, idx));
auto llvmType = typeConverter->convertType(element.getType());

Value result = rewriter.create<LLVM::ExtractElementOp>(loc, llvmType,
source, constIdx);
results[idx] = result;
}

rewriter.replaceOp(toElementsOp, results);
return success();
}
};

/// Conversion pattern for vector.step.
struct VectorScalableStepOpLowering
: public ConvertOpToLLVMPattern<vector::StepOp> {
Expand Down Expand Up @@ -2035,7 +2067,8 @@ void mlir::populateVectorToLLVMConversionPatterns(
VectorScalableInsertOpLowering, VectorScalableExtractOpLowering,
MaskedReductionOpConversion, VectorInterleaveOpLowering,
VectorDeinterleaveOpLowering, VectorFromElementsLowering,
VectorScalableStepOpLowering>(converter);
VectorToElementsLowering, VectorScalableStepOpLowering>(
converter);
}

void mlir::populateVectorToLLVMMatrixConversionPatterns(
Expand Down
40 changes: 39 additions & 1 deletion mlir/test/Conversion/VectorToLLVM/vector-to-llvm-interface.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -1875,7 +1875,7 @@ func.func @store_0d(%memref : memref<200x100xf32>, %i : index, %j : index) {
// CHECK: %[[CAST_MEMREF:.*]] = builtin.unrealized_conversion_cast %{{.*}} : memref<200x100xf32> to !llvm.struct<(ptr, ptr, i64, array<2 x i64>, array<2 x i64>)>
// CHECK: %[[CST:.*]] = arith.constant dense<1.100000e+01> : vector<f32>
// CHECK: %[[VAL:.*]] = builtin.unrealized_conversion_cast %[[CST]] : vector<f32> to vector<1xf32>
// CHECK: %[[REF:.*]] = llvm.extractvalue %[[CAST_MEMREF]][1] : !llvm.struct<(ptr, ptr, i64, array<2 x i64>, array<2 x i64>)>
// CHECK: %[[REF:.*]] = llvm.extractvalue %[[CAST_MEMREF]][1] : !llvm.struct<(ptr, ptr, i64, array<2 x i64>, array<2 x i64>)>
// CHECK: %[[C100:.*]] = llvm.mlir.constant(100 : index) : i64
// CHECK: %[[MUL:.*]] = llvm.mul %[[I]], %[[C100]] : i64
// CHECK: %[[ADD:.*]] = llvm.add %[[MUL]], %[[J]] : i64
Expand Down Expand Up @@ -2421,6 +2421,44 @@ func.func @from_elements_0d(%arg0: f32) -> vector<f32> {

// -----

//===----------------------------------------------------------------------===//
// vector.to_elements
//===----------------------------------------------------------------------===//

// CHECK-LABEL: func.func @to_elements_no_dead_elements
// CHECK-SAME: %[[A:.*]]: vector<4xf32>)
// CHECK: %[[C0:.*]] = llvm.mlir.constant(0 : i64) : i64
// CHECK: %[[ELEM0:.*]] = llvm.extractelement %[[A]][%[[C0]] : i64] : vector<4xf32>
// CHECK: %[[C1:.*]] = llvm.mlir.constant(1 : i64) : i64
// CHECK: %[[ELEM1:.*]] = llvm.extractelement %[[A]][%[[C1]] : i64] : vector<4xf32>
// CHECK: %[[C2:.*]] = llvm.mlir.constant(2 : i64) : i64
// CHECK: %[[ELEM2:.*]] = llvm.extractelement %[[A]][%[[C2]] : i64] : vector<4xf32>
// CHECK: %[[C3:.*]] = llvm.mlir.constant(3 : i64) : i64
// CHECK: %[[ELEM3:.*]] = llvm.extractelement %[[A]][%[[C3]] : i64] : vector<4xf32>
// CHECK: return %[[ELEM0]], %[[ELEM1]], %[[ELEM2]], %[[ELEM3]] : f32, f32, f32, f32
func.func @to_elements_no_dead_elements(%a: vector<4xf32>) -> (f32, f32, f32, f32) {
%0:4 = vector.to_elements %a : vector<4xf32>
return %0#0, %0#1, %0#2, %0#3 : f32, f32, f32, f32
}

// -----

// CHECK-LABEL: func.func @to_elements_dead_elements
// CHECK-SAME: %[[A:.*]]: vector<4xf32>)
// CHECK-NOT: llvm.mlir.constant(0 : i64) : i64
// CHECK: %[[C1:.*]] = llvm.mlir.constant(1 : i64) : i64
// CHECK: %[[ELEM1:.*]] = llvm.extractelement %[[A]][%[[C1]] : i64] : vector<4xf32>
// CHECK-NOT: llvm.mlir.constant(2 : i64) : i64
// CHECK: %[[C3:.*]] = llvm.mlir.constant(3 : i64) : i64
// CHECK: %[[ELEM3:.*]] = llvm.extractelement %[[A]][%[[C3]] : i64] : vector<4xf32>
// CHECK: return %[[ELEM1]], %[[ELEM3]] : f32, f32
func.func @to_elements_dead_elements(%a: vector<4xf32>) -> (f32, f32) {
%0:4 = vector.to_elements %a : vector<4xf32>
return %0#1, %0#3 : f32, f32
}

// -----

//===----------------------------------------------------------------------===//
// vector.step
//===----------------------------------------------------------------------===//
Expand Down
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