Index: lib/Support/StringMap.cpp
===================================================================
--- lib/Support/StringMap.cpp
+++ lib/Support/StringMap.cpp
@@ -22,6 +22,13 @@
   
   // If a size is specified, initialize the table with that many buckets.
   if (InitSize) {
+    // The table will grow when the number of entries reach 3/4 of the number of
+    // buckets. To guarantee that "InitSize" number of entries can be inserted
+    // in the table without growing, we allocate just what is needed here.
+    InitSize = (InitSize * 4 + 2) / 3;
+    // Size has to be a power of 2
+    if (!isPowerOf2_32(InitSize))
+      InitSize = NextPowerOf2(InitSize);
     init(InitSize);
     return;
   }
Index: unittests/ADT/StringMapTest.cpp
===================================================================
--- unittests/ADT/StringMapTest.cpp
+++ unittests/ADT/StringMapTest.cpp
@@ -231,12 +231,12 @@
   // moved to a different bucket during internal rehashing. This depends on
   // the particular key, and the implementation of StringMap and HashString.
   // Changes to those might result in this test not actually checking that.
-  StringMap<uint32_t> t(1);
-  EXPECT_EQ(1u, t.getNumBuckets());
+  StringMap<uint32_t> t(0);
+  EXPECT_EQ(0u, t.getNumBuckets());
 
   StringMap<uint32_t>::iterator It =
     t.insert(std::make_pair("abcdef", 42)).first;
-  EXPECT_EQ(2u, t.getNumBuckets());
+  EXPECT_EQ(16u, t.getNumBuckets());
   EXPECT_EQ("abcdef", It->first());
   EXPECT_EQ(42u, It->second);
 }