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Revert "[MLIR][SCF] Sink scf.if from scf.while before region into after region in scf-uplift-while-to-for" #169888

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Merged
NexMing merged 1 commit into from
Dec 1, 2025
Merged

Revert "[MLIR][SCF] Sink scf.if from scf.while before region into after region in scf-uplift-while-to-for" #169888

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79 changes: 1 addition & 78 deletions mlir/lib/Dialect/SCF/Transforms/UpliftWhileToFor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -19,83 +19,6 @@
using namespace mlir;

namespace {
/// Move an scf.if op that is directly before the scf.condition op in the while
/// before region, and whose condition matches the condition of the
/// scf.condition op, down into the while after region.
///
/// scf.while (%init) : (...) -> ... {
/// %cond = ...
/// %res = scf.if %cond -> (...) {
/// use1(%init)
/// %then_val = ...
/// ... // then block
/// scf.yield %then_val
/// } else {
/// scf.yield %init
/// }
/// scf.condition(%cond) %res
/// } do {
/// ^bb0(%arg):
/// use2(%arg)
/// ...
///
/// becomes
/// scf.while (%init) : (...) -> ... {
/// %cond = ...
/// scf.condition(%cond) %init
/// } do {
/// ^bb0(%arg): :
/// use1(%arg)
/// ... // if then block
/// %then_val = ...
/// use2(%then_val)
/// ...
struct WhileMoveIfDown : public OpRewritePattern<scf::WhileOp> {
using OpRewritePattern<scf::WhileOp>::OpRewritePattern;

LogicalResult matchAndRewrite(scf::WhileOp op,
PatternRewriter &rewriter) const override {
// Check that the first opeation produces one result and that result must
// have exactly two uses (these two uses come from the `scf.if` and
// `scf.condition` operations).
Operation &condOp = op.getBeforeBody()->front();
if (condOp.getNumResults() != 1 || !condOp.getResult(0).hasNUses(2))
return failure();

Value condVal = condOp.getResult(0);
auto ifOp = dyn_cast<scf::IfOp>(condOp.getNextNode());
if (!ifOp || ifOp.getCondition() != condVal)
return failure();

auto term = dyn_cast<scf::ConditionOp>(ifOp->getNextNode());
if (!term || term.getCondition() != condVal)
return failure();

// Check that if results and else yield operands match the scf.condition op
// arguments and while before arguments respectively.
if (!llvm::equal(ifOp->getResults(), term.getArgs()) ||
!llvm::equal(ifOp.elseYield()->getOperands(), op.getBeforeArguments()))
return failure();

// Update uses and move the if op into the after region.
rewriter.replaceAllUsesWith(op.getAfterArguments(),
ifOp.thenYield()->getOperands());
rewriter.replaceUsesWithIf(op.getBeforeArguments(), op.getAfterArguments(),
[&](OpOperand &use) {
return ifOp.getThenRegion().isAncestor(
use.getOwner()->getParentRegion());
});
rewriter.modifyOpInPlace(
term, [&]() { term.getArgsMutable().assign(op.getBeforeArguments()); });

rewriter.eraseOp(ifOp.thenYield());
rewriter.inlineBlockBefore(ifOp.thenBlock(), op.getAfterBody(),
op.getAfterBody()->begin());
rewriter.eraseOp(ifOp);
return success();
}
};

struct UpliftWhileOp : public OpRewritePattern<scf::WhileOp> {
using OpRewritePattern::OpRewritePattern;

Expand Down Expand Up @@ -344,5 +267,5 @@ FailureOr<scf::ForOp> mlir::scf::upliftWhileToForLoop(RewriterBase &rewriter,
}

void mlir::scf::populateUpliftWhileToForPatterns(RewritePatternSet &patterns) {
patterns.add<UpliftWhileOp, WhileMoveIfDown>(patterns.getContext());
patterns.add<UpliftWhileOp>(patterns.getContext());
}
31 changes: 0 additions & 31 deletions mlir/test/Dialect/SCF/uplift-while.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -185,34 +185,3 @@ func.func @uplift_while(%arg0: index, %arg1: index, %arg2: index) -> (i32, f32)
// CHECK: %[[T2:.*]] = "test.test2"(%[[ARG2]]) : (f32) -> f32
// CHECK: scf.yield %[[T1]], %[[T2]] : i32, f32
// CHECK: return %[[RES]]#0, %[[RES]]#1 : i32, f32

// -----

func.func @uplift_while(%low: index, %upper: index, %val : i32) -> i32 {
%c1 = arith.constant 1 : index
%1:2 = scf.while (%iv = %low, %iter = %val) : (index, i32) -> (index, i32) {
%2 = arith.cmpi slt, %iv, %upper : index
%3:2 = scf.if %2 -> (index, i32) {
%4 = "test.test"(%iter) : (i32) -> i32
%5 = arith.addi %iv, %c1 : index
scf.yield %5, %4 : index, i32
} else {
scf.yield %iv, %iter : index, i32
}
scf.condition(%2) %3#0, %3#1 : index, i32
} do {
^bb0(%arg0: index, %arg1: i32):
scf.yield %arg0, %arg1 : index, i32
}
return %1#1 : i32
}

// CHECK-LABEL: func.func @uplift_while(
// CHECK-SAME: %[[ARG0:.*]]: index, %[[ARG1:.*]]: index, %[[ARG2:.*]]: i32) -> i32 {
// CHECK: %[[CONSTANT_0:.*]] = arith.constant 1 : index
// CHECK: %[[FOR_0:.*]] = scf.for %[[VAL_0:.*]] = %[[ARG0]] to %[[ARG1]] step %[[CONSTANT_0]] iter_args(%[[VAL_1:.*]] = %[[ARG2]]) -> (i32) {
// CHECK: %[[VAL_2:.*]] = "test.test"(%[[VAL_1]]) : (i32) -> i32
// CHECK: scf.yield %[[VAL_2]] : i32
// CHECK: }
// CHECK: return %[[FOR_0]] : i32
// CHECK: }