IndexedMap: Document why SmallVector<T, 0> is preferable here.

llvm-svn: 231028
llvm · Mar 2, 2015 · bb76eaa · bb76eaa
1 parent 59e8c3b
commit bb76eaa
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/llvm/include/llvm/ADT/IndexedMap.h b/llvm/include/llvm/ADT/IndexedMap.h
@@ -30,6 +30,9 @@ namespace llvm {
 template <typename T, typename ToIndexT = llvm::identity<unsigned> >
   class IndexedMap {
     typedef typename ToIndexT::argument_type IndexT;
+    // Prefer SmallVector with zero inline storage over std::vector. IndexedMaps
+    // can grow very large and SmallVector grows more efficiently as long as T
+    // is trivially copyable.
     typedef SmallVector<T, 0> StorageT;
     StorageT storage_;
     T nullVal_;