[ADT] Remove DenseMap::init (NFC)

This patch removes DenseMap::init and SmallDenseMap::init by inlining
them into their call sites and simplifying them.

init() is defined as:

  void init(unsigned InitNumEntries) {
    auto InitBuckets = BaseT::getMinBucketToReserveForEntries(InitNumEntries);
    this->initWithExactBucketCount(InitBuckets);
  }

- Constuctors: Now that we have constructors that allocate the exact
  number of buckets (as opposed to the number of key/value pairs),
  init() does too much.  Once we convert the number of key/value pairs
  to the number of buckets, we can call the constructors that take the
  exact number of buckets.

- init(0) in the move assignment operators simplifies down to:

    initWithExactBucketCount(0)

- shrink_and_clear() computes the number of buckets to have after the
  clear operation.  As such, we should call initWithExactBucketCount,
  not init.  Otherwise, we would end up adding "load factor padding"
  on top of NewNumBuckets:

    NextPowerOf2(NewNumBuckets * 4 / 3 + 1)

All in all, init() doesn't bring any value in the current setup.

This patch is part of the effort outlined in #168255.

Author: kazutakahirata

llvm/include/llvm/ADT/DenseMap.h

@@ -162,7 +162,7 @@ class DenseMapBase : public DebugEpochBase {
       return;
     }
     derived().deallocateBuckets();
-    derived().init(NewNumBuckets);
+    initWithExactBucketCount(NewNumBuckets);
   }
 
   /// Return true if the specified key is in the map, false otherwise.
@@ -750,9 +750,9 @@ class DenseMap : public DenseMapBase<DenseMap<KeyT, ValueT, KeyInfoT, BucketT>,
 public:
   /// Create a DenseMap with an optional \p NumElementsToReserve to guarantee
   /// that this number of elements can be inserted in the map without grow().
-  explicit DenseMap(unsigned NumElementsToReserve = 0) {
-    init(NumElementsToReserve);
-  }
+  explicit DenseMap(unsigned NumElementsToReserve = 0)
+      : DenseMap(BaseT::getMinBucketToReserveForEntries(NumElementsToReserve),
+                 typename BaseT::ExactBucketCount{}) {}
 
   DenseMap(const DenseMap &other) : DenseMap() { this->copyFrom(other); }
 
@@ -784,7 +784,7 @@ class DenseMap : public DenseMapBase<DenseMap<KeyT, ValueT, KeyInfoT, BucketT>,
   DenseMap &operator=(DenseMap &&other) {
     this->destroyAll();
     deallocateBuckets();
-    init(0);
+    this->initWithExactBucketCount(0);
     this->swap(other);
     return *this;
   }
@@ -825,11 +825,6 @@ class DenseMap : public DenseMapBase<DenseMap<KeyT, ValueT, KeyInfoT, BucketT>,
     return true;
   }
 
-  void init(unsigned InitNumEntries) {
-    auto InitBuckets = BaseT::getMinBucketToReserveForEntries(InitNumEntries);
-    this->initWithExactBucketCount(InitBuckets);
-  }
-
   // Put the zombie instance in a known good state after a move.
   void kill() {
     deallocateBuckets();
@@ -898,9 +893,10 @@ class SmallDenseMap
   }
 
 public:
-  explicit SmallDenseMap(unsigned NumElementsToReserve = 0) {
-    init(NumElementsToReserve);
-  }
+  explicit SmallDenseMap(unsigned NumElementsToReserve = 0)
+      : SmallDenseMap(
+            BaseT::getMinBucketToReserveForEntries(NumElementsToReserve),
+            typename BaseT::ExactBucketCount{}) {}
 
   SmallDenseMap(const SmallDenseMap &other) : SmallDenseMap() {
     this->copyFrom(other);
@@ -935,7 +931,7 @@ class SmallDenseMap
   SmallDenseMap &operator=(SmallDenseMap &&other) {
     this->destroyAll();
     deallocateBuckets();
-    init(0);
+    this->initWithExactBucketCount(0);
     this->swap(other);
     return *this;
   }
@@ -1091,11 +1087,6 @@ class SmallDenseMap
     return true;
   }
 
-  void init(unsigned InitNumEntries) {
-    auto InitBuckets = BaseT::getMinBucketToReserveForEntries(InitNumEntries);
-    this->initWithExactBucketCount(InitBuckets);
-  }
-
   // Put the zombie instance in a known good state after a move.
   void kill() {
     deallocateBuckets();