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[ADT] Simplify DenseMapIterator with std::reverse_iterator (NFC) #157389

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Sep 10, 2025
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[ADT] Simplify DenseMapIterator with std::reverse_iterator (NFC) #157389

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55 changes: 23 additions & 32 deletions llvm/include/llvm/ADT/DenseMap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1184,10 +1184,14 @@ class DenseMapIterator : DebugEpochBase::HandleBase {
using iterator_category = std::forward_iterator_tag;

private:
pointer Ptr = nullptr;
pointer End = nullptr;
using BucketItTy =
std::conditional_t<shouldReverseIterate<KeyT>(),
std::reverse_iterator<pointer>, pointer>;

DenseMapIterator(pointer Pos, pointer E, const DebugEpochBase &Epoch)
BucketItTy Ptr = {};
BucketItTy End = {};

DenseMapIterator(BucketItTy Pos, BucketItTy E, const DebugEpochBase &Epoch)
: DebugEpochBase::HandleBase(&Epoch), Ptr(Pos), End(E) {
assert(isHandleInSync() && "invalid construction!");
}
Expand All @@ -1201,29 +1205,24 @@ class DenseMapIterator : DebugEpochBase::HandleBase {
// empty buckets.
if (IsEmpty)
return makeEnd(Buckets, Epoch);
if (shouldReverseIterate<KeyT>()) {
DenseMapIterator Iter(Buckets.end(), Buckets.begin(), Epoch);
Iter.RetreatPastEmptyBuckets();
return Iter;
}
DenseMapIterator Iter(Buckets.begin(), Buckets.end(), Epoch);
auto R = maybeReverse(Buckets);
DenseMapIterator Iter(R.begin(), R.end(), Epoch);
Iter.AdvancePastEmptyBuckets();
return Iter;
}

static DenseMapIterator makeEnd(iterator_range<pointer> Buckets,
const DebugEpochBase &Epoch) {
if (shouldReverseIterate<KeyT>())
return DenseMapIterator(Buckets.begin(), Buckets.begin(), Epoch);
return DenseMapIterator(Buckets.end(), Buckets.end(), Epoch);
auto R = maybeReverse(Buckets);
return DenseMapIterator(R.end(), R.end(), Epoch);
}

static DenseMapIterator makeIterator(pointer P,
iterator_range<pointer> Buckets,
const DebugEpochBase &Epoch) {
if (shouldReverseIterate<KeyT>())
return DenseMapIterator(P + 1, Buckets.begin(), Epoch);
return DenseMapIterator(P, Buckets.end(), Epoch);
auto R = maybeReverse(Buckets);
constexpr int Offset = shouldReverseIterate<KeyT>() ? 1 : 0;
return DenseMapIterator(BucketItTy(P + Offset), R.end(), Epoch);
}

// Converting ctor from non-const iterators to const iterators. SFINAE'd out
Expand All @@ -1238,16 +1237,16 @@ class DenseMapIterator : DebugEpochBase::HandleBase {
reference operator*() const {
assert(isHandleInSync() && "invalid iterator access!");
assert(Ptr != End && "dereferencing end() iterator");
if (shouldReverseIterate<KeyT>())
return Ptr[-1];
return *Ptr;
}
pointer operator->() const { return &operator*(); }

friend bool operator==(const DenseMapIterator &LHS,
const DenseMapIterator &RHS) {
assert((!LHS.Ptr || LHS.isHandleInSync()) && "handle not in sync!");
assert((!RHS.Ptr || RHS.isHandleInSync()) && "handle not in sync!");
assert((!LHS.getEpochAddress() || LHS.isHandleInSync()) &&
"handle not in sync!");
assert((!RHS.getEpochAddress() || RHS.isHandleInSync()) &&
"handle not in sync!");
assert(LHS.getEpochAddress() == RHS.getEpochAddress() &&
"comparing incomparable iterators!");
return LHS.Ptr == RHS.Ptr;
Expand All @@ -1261,11 +1260,6 @@ class DenseMapIterator : DebugEpochBase::HandleBase {
inline DenseMapIterator &operator++() { // Preincrement
assert(isHandleInSync() && "invalid iterator access!");
assert(Ptr != End && "incrementing end() iterator");
if (shouldReverseIterate<KeyT>()) {
--Ptr;
RetreatPastEmptyBuckets();
return *this;
}
++Ptr;
AdvancePastEmptyBuckets();
return *this;
Expand All @@ -1288,14 +1282,11 @@ class DenseMapIterator : DebugEpochBase::HandleBase {
++Ptr;
}

void RetreatPastEmptyBuckets() {
assert(Ptr >= End);
const KeyT Empty = KeyInfoT::getEmptyKey();
const KeyT Tombstone = KeyInfoT::getTombstoneKey();

while (Ptr != End && (KeyInfoT::isEqual(Ptr[-1].getFirst(), Empty) ||
KeyInfoT::isEqual(Ptr[-1].getFirst(), Tombstone)))
--Ptr;
static auto maybeReverse(iterator_range<pointer> Range) {
if constexpr (shouldReverseIterate<KeyT>())
return reverse(Range);
else
return Range;
}
};

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