From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Mon, 2 Mar 2015 22:20:22 +0000 (+0000)
Subject: IndexedMap: Document why SmallVector<T, 0> is preferable here.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0b08b96fdd9e9768aacbac5c5533624a48b34c42;p=oota-llvm.git

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231028 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/ADT/IndexedMap.h b/include/llvm/ADT/IndexedMap.h
index a830a41f56d..5ba85c02792 100644
--- a/include/llvm/ADT/IndexedMap.h
+++ b/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_;