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[LV] Extend FindFirstIV to unsigned case #146386

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[LV] Extend FindFirstIV to unsigned case #146386

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5ab0a61
[LV] Extend FindFirstIV to unsigned case
artagnon Jun 30, 2025
e59b1c9
[LV] Add negative test
artagnon Jul 3, 2025
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6 changes: 5 additions & 1 deletion llvm/include/llvm/Analysis/IVDescriptors.h
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,9 @@ enum class RecurKind {
FindFirstIVSMin, /// FindFirst reduction with select(icmp(),x,y) where one of
///< (x,y) is a decreasing loop induction, and both x and y
///< are integer type, producing a SMin reduction.
FindFirstIVUMin, /// FindFirst reduction with select(icmp(),x,y) where one of
///< (x,y) is a decreasing loop induction, and both x and y
///< are integer type, producing a UMin reduction.
FindLastIVSMax, ///< FindLast reduction with select(cmp(),x,y) where one of
///< (x,y) is increasing loop induction, and both x and y
///< are integer type, producing a SMax reduction.
Expand Down Expand Up @@ -265,7 +268,8 @@ class RecurrenceDescriptor {
/// Returns true if the recurrence kind is of the form
/// select(cmp(),x,y) where one of (x,y) is decreasing loop induction.
static bool isFindFirstIVRecurrenceKind(RecurKind Kind) {
return Kind == RecurKind::FindFirstIVSMin;
return Kind == RecurKind::FindFirstIVSMin ||
Kind == RecurKind::FindFirstIVUMin;
}

/// Returns true if the recurrence kind is of the form
Expand Down
11 changes: 7 additions & 4 deletions llvm/lib/Analysis/IVDescriptors.cpp
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Expand Up @@ -51,6 +51,7 @@ bool RecurrenceDescriptor::isIntegerRecurrenceKind(RecurKind Kind) {
case RecurKind::UMin:
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
return true;
Expand Down Expand Up @@ -741,10 +742,9 @@ RecurrenceDescriptor::isFindIVPattern(RecurKind Kind, Loop *TheLoop,
: APInt::getMinValue(NumBits);
ValidRange = ConstantRange::getNonEmpty(Sentinel + 1, Sentinel);
} else {
assert(IsSigned && "Only FindFirstIV with SMax is supported currently");
ValidRange =
ConstantRange::getNonEmpty(APInt::getSignedMinValue(NumBits),
APInt::getSignedMaxValue(NumBits) - 1);
APInt Sentinel = IsSigned ? APInt::getSignedMaxValue(NumBits)
: APInt::getMaxValue(NumBits);
ValidRange = ConstantRange::getNonEmpty(Sentinel, Sentinel - 1);
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@david-arm david-arm Jul 3, 2025 •
edited
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Is this right? I thought the point of the range was to include everything except the sentinel, but if I've understood ConstantRange::getNonEmpty correctly it creates the range [Lower, Upper) where in this case Lower == Sentinel. This means Sentinel is included in the range? This seems to contradict the findlastiv case where we create the range [Sentinel + 1, Sentinel)

}

LLVM_DEBUG(dbgs() << "LV: "
Expand All @@ -770,6 +770,8 @@ RecurrenceDescriptor::isFindIVPattern(RecurKind Kind, Loop *TheLoop,

if (CheckRange(true))
return RecurKind::FindFirstIVSMin;
if (CheckRange(false))
return RecurKind::FindFirstIVUMin;
return std::nullopt;
};

Expand Down Expand Up @@ -1183,6 +1185,7 @@ unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
return Instruction::Mul;
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
case RecurKind::Or:
Expand Down
3 changes: 3 additions & 0 deletions llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
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Expand Up @@ -23181,6 +23181,7 @@ class HorizontalReduction {
case RecurKind::FMulAdd:
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
case RecurKind::FMaximumNum:
Expand Down Expand Up @@ -23317,6 +23318,7 @@ class HorizontalReduction {
case RecurKind::FMulAdd:
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
case RecurKind::FMaximumNum:
Expand Down Expand Up @@ -23418,6 +23420,7 @@ class HorizontalReduction {
case RecurKind::FMulAdd:
case RecurKind::AnyOf:
case RecurKind::FindFirstIVSMin:
case RecurKind::FindFirstIVUMin:
case RecurKind::FindLastIVSMax:
case RecurKind::FindLastIVUMax:
case RecurKind::FMaximumNum:
Expand Down
10 changes: 3 additions & 7 deletions llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
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Expand Up @@ -743,14 +743,10 @@ Value *VPInstruction::generate(VPTransformState &State) {
Value *ReducedPartRdx = State.get(getOperand(3));
RecurKind MinMaxKind;
bool IsSigned = RecurrenceDescriptor::isSignedRecurrenceKind(RK);
if (RecurrenceDescriptor::isFindLastIVRecurrenceKind(RK)) {
if (RecurrenceDescriptor::isFindLastIVRecurrenceKind(RK))
MinMaxKind = IsSigned ? RecurKind::SMax : RecurKind::UMax;
} else {
assert(RecurrenceDescriptor::isFindFirstIVRecurrenceKind(RK) &&
"Kind must either be FindLastIV or FindFirstIV");
assert(IsSigned && "Only FindFirstIV with SMax is currently supported");
MinMaxKind = RecurKind::SMin;
}
else
MinMaxKind = IsSigned ? RecurKind::SMin : RecurKind::UMin;
for (unsigned Part = 1; Part < UF; ++Part)
ReducedPartRdx = createMinMaxOp(Builder, MinMaxKind, ReducedPartRdx,
State.get(getOperand(3 + Part)));
Expand Down
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