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Revert "[mlir][affine] Add fold logic when the affine.yield has IV as operand in the AffineForEmptyLoopFolder" #165607

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Merged
merged 1 commit into from
Oct 29, 2025
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Revert "[mlir][affine] Add fold logic when the affine.yield has IV as operand in the AffineForEmptyLoopFolder" #165607

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29 changes: 5 additions & 24 deletions mlir/lib/Dialect/Affine/IR/AffineOps.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2610,21 +2610,6 @@ static std::optional<uint64_t> getTrivialConstantTripCount(AffineForOp forOp) {
return ub - lb <= 0 ? 0 : (ub - lb + step - 1) / step;
}

/// Calculate the constant value of the loop's induction variable for its last
/// trip.
static std::optional<int64_t>
getConstantInductionVarForLastTrip(AffineForOp forOp) {
std::optional<uint64_t> tripCount = getTrivialConstantTripCount(forOp);
if (!tripCount.has_value())
return std::nullopt;
if (tripCount.value() == 0)
return std::nullopt;
int64_t lb = forOp.getConstantLowerBound();
int64_t step = forOp.getStepAsInt();
int64_t lastTripIv = lb + (tripCount.value() - 1) * step;
return lastTripIv;
}

/// Fold the empty loop.
static SmallVector<OpFoldResult> AffineForEmptyLoopFolder(AffineForOp forOp) {
if (!llvm::hasSingleElement(*forOp.getBody()))
Expand All @@ -2637,22 +2622,18 @@ static SmallVector<OpFoldResult> AffineForEmptyLoopFolder(AffineForOp forOp) {
// results.
return forOp.getInits();
}
SmallVector<OpFoldResult, 4> replacements;
SmallVector<Value, 4> replacements;
auto yieldOp = cast<AffineYieldOp>(forOp.getBody()->getTerminator());
auto iterArgs = forOp.getRegionIterArgs();
bool hasValDefinedOutsideLoop = false;
bool iterArgsNotInOrder = false;
for (unsigned i = 0, e = yieldOp->getNumOperands(); i < e; ++i) {
Value val = yieldOp.getOperand(i);
BlockArgument *iterArgIt = llvm::find(iterArgs, val);
if (val == forOp.getInductionVar()) {
if (auto lastTripIv = getConstantInductionVarForLastTrip(forOp)) {
replacements.push_back(IntegerAttr::get(
IndexType::get(forOp.getContext()), lastTripIv.value()));
continue;
}
// TODO: It should be possible to perform a replacement by computing the
// last value of the IV based on the bounds and the step.
if (val == forOp.getInductionVar())
return {};
}
if (iterArgIt == iterArgs.end()) {
// `val` is defined outside of the loop.
assert(forOp.isDefinedOutsideOfLoop(val) &&
Expand All @@ -2675,7 +2656,7 @@ static SmallVector<OpFoldResult> AffineForEmptyLoopFolder(AffineForOp forOp) {
// out of order.
if (tripCount.has_value() && tripCount.value() >= 2 && iterArgsNotInOrder)
return {};
return replacements;
return llvm::to_vector_of<OpFoldResult>(replacements);
}

/// Canonicalize the bounds of the given loop.
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13 changes: 0 additions & 13 deletions mlir/test/Dialect/Affine/canonicalize.mlir
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Expand Up @@ -609,19 +609,6 @@ func.func @fold_zero_iter_loops(%in : index) -> index {

// -----

// CHECK-LABEL: func @fold_empty_loop_iv
// CHECK-SAME: %[[INIT:.*]]: index
func.func @fold_empty_loop_iv(%init: index) -> (index, index) {
%res:2 = affine.for %i = 0 to 10 step 1 iter_args(%arg0 = %init, %arg1 = %init) -> (index, index) {
affine.yield %i, %arg1 : index, index
}
// CHECK: %[[C9:.*]] = arith.constant 9 : index
// CHECK: return %[[C9]], %[[INIT]] : index, index
return %res#0, %res#1 : index, index
}

// -----

// CHECK-DAG: #[[$SET:.*]] = affine_set<(d0, d1)[s0] : (d0 >= 0, -d0 + 1022 >= 0, d1 >= 0, -d1 + s0 - 2 >= 0)>

// CHECK-LABEL: func @canonicalize_affine_if
Expand Down