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[ADT] Simplify SmallDenseMap::grow (NFC) #167829

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Merged
merged 2 commits into from
Nov 13, 2025
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[ADT] Simplify SmallDenseMap::grow (NFC) #167829

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[ADT] Simplify SmallDenseMap::grow (NFC)
kazutakahirata Nov 13, 2025
fc55791
Address a comment.
kazutakahirata Nov 13, 2025
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75 changes: 33 additions & 42 deletions llvm/include/llvm/ADT/DenseMap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -413,9 +413,7 @@ class DenseMapBase : public DebugEpochBase {
return NextPowerOf2(NumEntries * 4 / 3 + 1);
}

void moveFromOldBuckets(iterator_range<BucketT *> OldBuckets) {
initEmpty();

void moveFromImpl(iterator_range<BucketT *> OldBuckets) {
// Insert all the old elements.
const KeyT EmptyKey = KeyInfoT::getEmptyKey();
const KeyT TombstoneKey = KeyInfoT::getTombstoneKey();
Expand All @@ -438,6 +436,14 @@ class DenseMapBase : public DebugEpochBase {
}
}

void moveFromOldBuckets(iterator_range<BucketT *> OldBuckets) {
initEmpty();
moveFromImpl(OldBuckets);
}

// Move key/value from Other to *this. Other will be in a zombie state.
void moveFrom(DerivedT &Other) { moveFromImpl(Other.buckets()); }

void copyFrom(const DerivedT &other) {
this->destroyAll();
derived().deallocateBuckets();
Expand Down Expand Up @@ -889,6 +895,12 @@ class SmallDenseMap
/// a large bucket. This union will be discriminated by the 'Small' bit.
AlignedCharArrayUnion<BucketT[InlineBuckets], LargeRep> storage;

struct ExactBucketCount {};
SmallDenseMap(unsigned NumBuckets, ExactBucketCount) {
allocateBuckets(NumBuckets);
this->BaseT::initEmpty();
}

public:
explicit SmallDenseMap(unsigned NumElementsToReserve = 0) {
init(NumElementsToReserve);
Expand Down Expand Up @@ -1065,7 +1077,10 @@ class SmallDenseMap
}

void deallocateBuckets() {
if (Small)
// Fast path to deallocateBuckets in case getLargeRep()->NumBuckets == 0,
// just like destroyAll. This path is used to destruct zombie instances
// after moves.
if (Small || getLargeRep()->NumBuckets == 0)
return;

deallocate_buffer(getLargeRep()->Buckets,
Expand Down Expand Up @@ -1096,46 +1111,22 @@ class SmallDenseMap
if (AtLeast > InlineBuckets)
AtLeast = std::max<unsigned>(64, NextPowerOf2(AtLeast - 1));

if (Small) {
// First move the inline buckets into a temporary storage.
AlignedCharArrayUnion<BucketT[InlineBuckets]> TmpStorage;
BucketT *TmpBegin = reinterpret_cast<BucketT *>(&TmpStorage);
BucketT *TmpEnd = TmpBegin;
SmallDenseMap Tmp(AtLeast, ExactBucketCount{});
Tmp.moveFrom(*this);

// Loop over the buckets, moving non-empty, non-tombstones into the
// temporary storage. Have the loop move the TmpEnd forward as it goes.
const KeyT EmptyKey = KeyInfoT::getEmptyKey();
const KeyT TombstoneKey = KeyInfoT::getTombstoneKey();
for (BucketT &B : inlineBuckets()) {
if (!KeyInfoT::isEqual(B.getFirst(), EmptyKey) &&
!KeyInfoT::isEqual(B.getFirst(), TombstoneKey)) {
assert(size_t(TmpEnd - TmpBegin) < InlineBuckets &&
"Too many inline buckets!");
::new (&TmpEnd->getFirst()) KeyT(std::move(B.getFirst()));
::new (&TmpEnd->getSecond()) ValueT(std::move(B.getSecond()));
++TmpEnd;
B.getSecond().~ValueT();
}
B.getFirst().~KeyT();
}

// AtLeast == InlineBuckets can happen if there are many tombstones,
// and grow() is used to remove them. Usually we always switch to the
// large rep here.
allocateBuckets(AtLeast);
this->moveFromOldBuckets(llvm::make_range(TmpBegin, TmpEnd));
return;
if (Tmp.Small) {
// Use moveFrom in those rare cases where we stay in the small mode. This
// can happen when we have many tombstones.
this->BaseT::initEmpty();
this->moveFrom(Tmp);
Tmp.Small = false;
Tmp.getLargeRep()->NumBuckets = 0;
} else {
Small = false;
NumTombstones = 0;
*getLargeRep() = std::move(*Tmp.getLargeRep());
Tmp.getLargeRep()->NumBuckets = 0;
}

LargeRep OldRep = std::move(*getLargeRep());
getLargeRep()->~LargeRep();
allocateBuckets(AtLeast);

this->moveFromOldBuckets(OldRep.buckets());

// Free the old table.
deallocate_buffer(OldRep.Buckets, sizeof(BucketT) * OldRep.NumBuckets,
alignof(BucketT));
}

// Plan how to shrink the bucket table. Return:
Expand Down
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