Microoptimize DenseMap::clear.

Cache NumEntries locally, it's only used in an assert and using the member
variable prevents the compiler from eliminating the tombstone check for types
with trivial destructors. No functionality change intended.

llvm-svn: 234589

llvm/include/llvm/ADT/DenseMap.h

@@ -100,16 +100,18 @@ public:
     }
 
     const KeyT EmptyKey = getEmptyKey(), 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();
-          decrementNumEntries();
+          --NumEntries;
         }
         P->getFirst() = EmptyKey;
       }
     }
-    assert(getNumEntries() == 0 && "Node count imbalance!");
+    assert(NumEntries == 0 && "Node count imbalance!");
+    setNumEntries(0);
     setNumTombstones(0);
   }
 
@@ -257,7 +259,7 @@ public:
   const void *getPointerIntoBucketsArray() const { return getBuckets(); }
 
 protected:
-  DenseMapBase() {}
+  DenseMapBase() = default;
 
   void destroyAll() {
     if (getNumBuckets() == 0) // Nothing to do.