[ADT] Use range-based for loops in DenseMap.h (NFC) (llvm#151900)

This patch introduces helper function buckets() to convert several
loops to range-based for loops.

Author: kazutakahirata

llvm/include/llvm/ADT/DenseMap.h

@@ -142,18 +142,18 @@ class DenseMapBase : public DebugEpochBase {
     const KeyT EmptyKey = getEmptyKey();
     if constexpr (std::is_trivially_destructible_v<ValueT>) {
       // Use a simpler loop when values don't need destruction.
-      for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P)
-        P->getFirst() = EmptyKey;
+      for (BucketT &B : buckets())
+        B.getFirst() = EmptyKey;
     } else {
       const KeyT TombstoneKey = getTombstoneKey();
       unsigned NumEntries = getNumEntries();
-      for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P) {
-        if (!KeyInfoT::isEqual(P->getFirst(), EmptyKey)) {
-          if (!KeyInfoT::isEqual(P->getFirst(), TombstoneKey)) {
-            P->getSecond().~ValueT();
+      for (BucketT &B : buckets()) {
+        if (!KeyInfoT::isEqual(B.getFirst(), EmptyKey)) {
+          if (!KeyInfoT::isEqual(B.getFirst(), TombstoneKey)) {
+            B.getSecond().~ValueT();
             --NumEntries;
           }
-          P->getFirst() = EmptyKey;
+          B.getFirst() = EmptyKey;
         }
       }
       assert(NumEntries == 0 && "Node count imbalance!");
@@ -424,11 +424,11 @@ class DenseMapBase : public DebugEpochBase {
       return;
 
     const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
-    for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P) {
-      if (!KeyInfoT::isEqual(P->getFirst(), EmptyKey) &&
-          !KeyInfoT::isEqual(P->getFirst(), TombstoneKey))
-        P->getSecond().~ValueT();
-      P->getFirst().~KeyT();
+    for (BucketT &B : buckets()) {
+      if (!KeyInfoT::isEqual(B.getFirst(), EmptyKey) &&
+          !KeyInfoT::isEqual(B.getFirst(), TombstoneKey))
+        B.getSecond().~ValueT();
+      B.getFirst().~KeyT();
     }
   }
 
@@ -439,8 +439,8 @@ class DenseMapBase : public DebugEpochBase {
     assert((getNumBuckets() & (getNumBuckets() - 1)) == 0 &&
            "# initial buckets must be a power of two!");
     const KeyT EmptyKey = getEmptyKey();
-    for (BucketT *B = getBuckets(), *E = getBucketsEnd(); B != E; ++B)
-      ::new (&B->getFirst()) KeyT(EmptyKey);
+    for (BucketT &B : buckets())
+      ::new (&B.getFirst()) KeyT(EmptyKey);
   }
 
   /// Returns the number of buckets to allocate to ensure that the DenseMap can
@@ -584,6 +584,10 @@ class DenseMapBase : public DebugEpochBase {
     return getBuckets() + getNumBuckets();
   }
 
+  iterator_range<BucketT *> buckets() {
+    return llvm::make_range(getBuckets(), getBucketsEnd());
+  }
+
   void grow(unsigned AtLeast) { static_cast<DerivedT *>(this)->grow(AtLeast); }
 
   void shrink_and_clear() { static_cast<DerivedT *>(this)->shrink_and_clear(); }