Improve allocation behavior of Multiset copying and addAll implementa…

…tions in both Guava versions.

RELNOTES=n/a

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=182573989

android/guava/src/com/google/common/collect/AbstractMapBasedMultiset.java

@@ -17,6 +17,7 @@
 package com.google.common.collect;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.collect.CollectPreconditions.checkNonnegative;
 
 import com.google.common.annotations.GwtCompatible;
@@ -220,6 +221,14 @@ Entry<E> result(int entryIndex) {
     };
   }
 
+  /** Allocation-free implementation of {@code target.addAll(this)}. */
+  void addTo(Multiset<? super E> target) {
+    checkNotNull(target);
+    for (int i = backingMap.firstIndex(); i >= 0; i = backingMap.nextIndex(i)) {
+      target.add(backingMap.getKey(i), backingMap.getValue(i));
+    }
+  }
+
   @Override
   final int distinctElements() {
     return backingMap.size();

android/guava/src/com/google/common/collect/Multisets.java

@@ -857,17 +857,43 @@ static boolean equalsImpl(Multiset<?> multiset, @NullableDecl Object object) {
 
   /** An implementation of {@link Multiset#addAll}. */
   static <E> boolean addAllImpl(Multiset<E> self, Collection<? extends E> elements) {
-    if (elements.isEmpty()) {
+    checkNotNull(self);
+    checkNotNull(elements);
+    if (elements instanceof Multiset) {
+      return addAllImpl(self, cast(elements));
+    } else if (elements.isEmpty()) {
       return false;
+    } else {
+      return Iterators.addAll(self, elements.iterator());
     }
-    if (elements instanceof Multiset) {
-      Multiset<? extends E> that = cast(elements);
-      for (Entry<? extends E> entry : that.entrySet()) {
+  }
+
+  /** A specialization of {@code addAllImpl} for when {@code elements} is itself a Multiset. */
+  private static <E> boolean addAllImpl(Multiset<E> self, Multiset<? extends E> elements) {
+    // It'd be nice if we could specialize for ImmutableMultiset here without also retaining
+    // its code when it's not in scope...
+    if (elements instanceof AbstractMapBasedMultiset) {
+      return addAllImpl(self, (AbstractMapBasedMultiset<? extends E>) elements);
+    } else if (elements.isEmpty()) {
+      return false;
+    } else {
+      for (Multiset.Entry<? extends E> entry : elements.entrySet()) {
         self.add(entry.getElement(), entry.getCount());
       }
-    } else {
-      Iterators.addAll(self, elements.iterator());
+      return true;
+    }
+  }
+
+  /**
+   * A specialization of {@code addAllImpl} for when {@code elements} is an
+   * AbstractMapBasedMultiset.
+   */
+  private static <E> boolean addAllImpl(
+      Multiset<E> self, AbstractMapBasedMultiset<? extends E> elements) {
+    if (elements.isEmpty()) {
+      return false;
     }
+    elements.addTo(self);
     return true;
   }
 

guava/src/com/google/common/collect/ImmutableMultiset.java

@@ -541,9 +541,7 @@ public Builder<E> add(E... elements) {
     public Builder<E> addAll(Iterable<? extends E> elements) {
       if (elements instanceof Multiset) {
         Multiset<? extends E> multiset = Multisets.cast(elements);
-        for (Entry<? extends E> entry : multiset.entrySet()) {
-          addCopies(entry.getElement(), entry.getCount());
-        }
+        multiset.forEachEntry((e, n) -> contents.add(checkNotNull(e), n));
       } else {
         super.addAll(elements);
       }

guava/src/com/google/common/collect/Multisets.java

@@ -889,17 +889,23 @@ static boolean equalsImpl(Multiset<?> multiset, @NullableDecl Object object) {
 
   /** An implementation of {@link Multiset#addAll}. */
   static <E> boolean addAllImpl(Multiset<E> self, Collection<? extends E> elements) {
-    if (elements.isEmpty()) {
-      return false;
-    }
+    checkNotNull(self);
+    checkNotNull(elements);
     if (elements instanceof Multiset) {
-      Multiset<? extends E> that = cast(elements);
-      for (Entry<? extends E> entry : that.entrySet()) {
-        self.add(entry.getElement(), entry.getCount());
-      }
+      return addAllImpl(self, cast(elements));
+    } else if (elements.isEmpty()) {
+      return false;
     } else {
-      Iterators.addAll(self, elements.iterator());
+      return Iterators.addAll(self, elements.iterator());
+    }
+  }
+
+  /** A specialization of {@code addAllImpl} for when {@code elements} is itself a Multiset. */
+  private static <E> boolean addAllImpl(Multiset<E> self, Multiset<? extends E> elements) {
+    if (elements.isEmpty()) {
+      return false;
     }
+    elements.forEachEntry(self::add);
     return true;
   }