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[LV] Explicitly disable in-loop reductions for AnyOf and FindIV. nfc #163541

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Merged
merged 1 commit into from
Nov 14, 2025
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[LV] Explicitly disable in-loop reductions for AnyOf and FindIV. nfc #163541

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12 changes: 7 additions & 5 deletions llvm/lib/Analysis/IVDescriptors.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1220,11 +1220,6 @@ unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
return Instruction::Add;
case RecurKind::Mul:
return Instruction::Mul;
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
case RecurKind::Or:
return Instruction::Or;
case RecurKind::And:
Expand All @@ -1248,6 +1243,13 @@ unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
case RecurKind::FMaximumNum:
case RecurKind::FMinimumNum:
return Instruction::FCmp;
case RecurKind::AnyOf:
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@fhahn fhahn Oct 15, 2025

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Could we still leave AnyOf to return Or to avoid the changes in llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp?

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@Mel-Chen Mel-Chen Oct 27, 2025

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I think we should maintain consistency in how we handle AnyOf and FindIV. In particular, AnyOf, whether it currently only supports integer types or will support floating-point types in the future, should consistently use Instruction::Or in ComputeAnyOfResult to fold each part.

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@fhahn fhahn Nov 12, 2025

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Ok sounds good to me.

case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
// TODO: Set AnyOf and FindIV to Instruction::Select once in-loop reductions
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@ayalz ayalz Nov 15, 2025

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The reason is that RecurrenceDescriptor::getOpcode was set to Instruction::Or, but the recurrence chains of AnyOf and FindIV do not actually contain an Instruction::Or.

Boolean recurrence chain of AnyOf could indeed contain a Select as in nextRed = currentCond ? true : prevRed, but could also contain an Or as in nextRed = currentCond | prevRed?

Integer recurrence chain of FindIV indeed contains a Select: nextRed = currentCond ? currentIV : prevRed, though it would be good to clarify when the opcode is Select rather than an ICmp/FCmp feeding it - as in min/max reductions whose chains may also contain a Select.

Suffice for now to leave behind a TODO to return a valid opcode once these kinds of recurrences support in-loop reduction.

// are supported.
Comment on lines +1251 to +1252
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@ayalz ayalz Nov 15, 2025

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Suggested change
// TODO: Set AnyOf and FindIV to Instruction::Select once in-loop reductions
// are supported.
// TODO: Set AnyOf and FindIV to Instruction::Select once in-loop reductions
// are supported.
llvm_unreachable("AnyOf and FindIV do not support in-loop");

rather than claiming they are Unknown recurrence operations?

Should the enclosing getOpcode() be renamed getInLoopOpcode()?

default:
llvm_unreachable("Unknown recurrence operation");
}
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7 changes: 6 additions & 1 deletion llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Expand Up @@ -6591,9 +6591,14 @@ void LoopVectorizationCostModel::collectInLoopReductions() {
if (RdxDesc.getRecurrenceType() != Phi->getType())
continue;

// In-loop AnyOf and FindIV reductions are not yet supported.
RecurKind Kind = RdxDesc.getRecurrenceKind();
if (RecurrenceDescriptor::isAnyOfRecurrenceKind(Kind) ||
RecurrenceDescriptor::isFindIVRecurrenceKind(Kind))
continue;

// If the target would prefer this reduction to happen "in-loop", then we
// want to record it as such.
RecurKind Kind = RdxDesc.getRecurrenceKind();
if (!PreferInLoopReductions && !useOrderedReductions(RdxDesc) &&
!TTI.preferInLoopReduction(Kind, Phi->getType()))
continue;
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7 changes: 3 additions & 4 deletions llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
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Expand Up @@ -821,10 +821,9 @@ Value *VPInstruction::generate(VPTransformState &State) {
auto *OrigPhi = cast<PHINode>(PhiR->getUnderlyingValue());
Value *ReducedPartRdx = State.get(getOperand(2));
for (unsigned Idx = 3; Idx < getNumOperands(); ++Idx)
ReducedPartRdx = Builder.CreateBinOp(
(Instruction::BinaryOps)RecurrenceDescriptor::getOpcode(
RecurKind::AnyOf),
State.get(getOperand(Idx)), ReducedPartRdx, "bin.rdx");
ReducedPartRdx =
Builder.CreateBinOp(Instruction::Or, State.get(getOperand(Idx)),
ReducedPartRdx, "bin.rdx");
return createAnyOfReduction(Builder, ReducedPartRdx,
State.get(getOperand(1), VPLane(0)), OrigPhi);
}
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