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[mlir][LLVM] Improve llvm.extractvalue folder #136861

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Merged
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Apr 23, 2025
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[mlir][LLVM] Improve llvm.extractvalue folder #136861

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47 changes: 39 additions & 8 deletions mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1885,11 +1885,40 @@ OpFoldResult LLVM::ExtractValueOp::fold(FoldAdaptor adaptor) {

auto insertValueOp = getContainer().getDefiningOp<InsertValueOp>();
OpFoldResult result = {};
ArrayRef<int64_t> extractPos = getPosition();
bool switchedToInsertedValue = false;
while (insertValueOp) {
if (getPosition() == insertValueOp.getPosition())
ArrayRef<int64_t> insertPos = insertValueOp.getPosition();
auto extractPosSize = extractPos.size();
auto insertPosSize = insertPos.size();

// Case 1: Exact match of positions.
if (extractPos == insertPos)
return insertValueOp.getValue();
unsigned min =
std::min(getPosition().size(), insertValueOp.getPosition().size());

// Case 2: Insert position is a prefix of extract position. Continue
// traversal with the inserted value. Example:
// ```
// %0 = llvm.insertvalue %arg1, %undef[0] : !llvm.struct<(i32, i32, i32)>
// %1 = llvm.insertvalue %arg2, %0[1] : !llvm.struct<(i32, i32, i32)>
// %2 = llvm.insertvalue %arg3, %1[2] : !llvm.struct<(i32, i32, i32)>
// %3 = llvm.insertvalue %2, %foo[0]
// : !llvm.struct<(struct<(i32, i32, i32)>, i64)>
// %4 = llvm.extractvalue %3[0, 0]
// : !llvm.struct<(struct<(i32, i32, i32)>, i64)>
// ```
// In the above example, %4 is folded to %arg1.
if (extractPosSize > insertPosSize &&
extractPos.take_front(insertPosSize) == insertPos) {
insertValueOp = insertValueOp.getValue().getDefiningOp<InsertValueOp>();
extractPos = extractPos.drop_front(insertPosSize);
switchedToInsertedValue = true;
continue;
}

// Case 3: Try to continue the traversal with the container value.
unsigned min = std::min(extractPosSize, insertPosSize);

// If one is fully prefix of the other, stop propagating back as it will
// miss dependencies. For instance, %3 should not fold to %f0 in the
// following example:
Expand All @@ -1900,15 +1929,17 @@ OpFoldResult LLVM::ExtractValueOp::fold(FoldAdaptor adaptor) {
// !llvm.array<4 x !llvm.array<4 x f32>>
// %3 = llvm.extractvalue %2[0, 0] : !llvm.array<4 x !llvm.array<4 x f32>>
// ```
if (getPosition().take_front(min) ==
insertValueOp.getPosition().take_front(min))
if (extractPos.take_front(min) == insertPos.take_front(min))
return result;

// If neither a prefix, nor the exact position, we can extract out of the
// value being inserted into. Moreover, we can try again if that operand
// is itself an insertvalue expression.
getContainerMutable().assign(insertValueOp.getContainer());
result = getResult();
if (!switchedToInsertedValue) {
// Do not swap out the container operand if we decided earlier to
// continue the traversal with the inserted value (Case 2).
getContainerMutable().assign(insertValueOp.getContainer());
result = getResult();
}
insertValueOp = insertValueOp.getContainer().getDefiningOp<InsertValueOp>();
}
return result;
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16 changes: 16 additions & 0 deletions mlir/test/Dialect/LLVMIR/canonicalize.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,22 @@ llvm.func @fold_extractvalue() -> i32 {

// -----

// CHECK-LABEL: fold_extractvalue(
// CHECK-SAME: %[[arg1:.*]]: i32, %[[arg2:.*]]: i32, %[[arg3:.*]]: i32)
// CHECK-NEXT: llvm.return %[[arg1]] : i32
llvm.func @fold_extractvalue(%arg1: i32, %arg2: i32, %arg3: i32) -> i32{
%3 = llvm.mlir.undef : !llvm.struct<(struct<(i32, i32, i32)>, struct<(i32, i32)>)>
%5 = llvm.mlir.undef : !llvm.struct<(i32, i32, i32)>
%6 = llvm.insertvalue %arg1, %5[0] : !llvm.struct<(i32, i32, i32)>
%7 = llvm.insertvalue %arg1, %6[1] : !llvm.struct<(i32, i32, i32)>
%8 = llvm.insertvalue %arg1, %7[2] : !llvm.struct<(i32, i32, i32)>
%11 = llvm.insertvalue %8, %3[0] : !llvm.struct<(struct<(i32, i32, i32)>, struct<(i32, i32)>)>
%13 = llvm.extractvalue %11[0, 0] : !llvm.struct<(struct<(i32, i32, i32)>, struct<(i32, i32)>)>
llvm.return %13 : i32
}

// -----

// CHECK-LABEL: no_fold_extractvalue
llvm.func @no_fold_extractvalue(%arr: !llvm.array<4 x f32>) -> f32 {
%f0 = arith.constant 0.0 : f32
Expand Down
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