Fix PR13148, an inf-loop in StringMap.

StringMap suffered from the same bug as DenseMap: when you explicitly
construct it with a small number of buckets, you can arrange for the
tombstone-based growth path to be followed when the number of buckets
was less than '8'. In that case, even with a full map, it would compare
'0' as not less than '0', and refuse to grow the table, leading to
inf-loops trying to find an empty bucket on the next insertion. The fix
is very simple: use '<=' as the comparison. The same fix was applied to
DenseMap as well during its recent refactoring.

Thanks to Alex Bolz for the great report and test case. =]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158725 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 1 deletions

diff --git a/lib/Support/StringMap.cpp b/lib/Support/StringMap.cpp
index c131fe07f4..c2fc261df3 100644
--- a/lib/Support/StringMap.cpp
+++ b/lib/Support/StringMap.cpp
@@ -189,7 +189,7 @@ void StringMapImpl::RehashTable() {
   // grow/rehash the table.
   if (NumItems*4 > NumBuckets*3) {
     NewSize = NumBuckets*2;
-  } else if (NumBuckets-(NumItems+NumTombstones) < NumBuckets/8) {
+  } else if (NumBuckets-(NumItems+NumTombstones) <= NumBuckets/8) {
     NewSize = NumBuckets;
   } else {
     return;
diff --git a/unittests/ADT/StringMapTest.cpp b/unittests/ADT/StringMapTest.cpp
index 66e04933ad..5bb65cbd7a 100644
--- a/unittests/ADT/StringMapTest.cpp
+++ b/unittests/ADT/StringMapTest.cpp
@@ -134,6 +134,28 @@ TEST_F(StringMapTest, InsertAndEraseTest) {
   assertSingleItemMap();
 }
 
+TEST_F(StringMapTest, SmallFullMapTest) {
+  // StringMap has a tricky corner case when the map is small (<8 buckets) and
+  // it fills up through a balanced pattern of inserts and erases. This can
+  // lead to inf-loops in some cases (PR13148) so we test it explicitly here.
+  llvm::StringMap<int> Map(2);
+
+  Map["eins"] = 1;
+  Map["zwei"] = 2;
+  Map["drei"] = 3;
+  Map.erase("drei");
+  Map.erase("eins");
+  Map["veir"] = 4;
+  Map["funf"] = 5;
+
+  EXPECT_EQ(3u, Map.size());
+  EXPECT_EQ(0, Map.lookup("eins"));
+  EXPECT_EQ(2, Map.lookup("zwei"));
+  EXPECT_EQ(0, Map.lookup("drei"));
+  EXPECT_EQ(4, Map.lookup("veir"));
+  EXPECT_EQ(5, Map.lookup("funf"));
+}
+
 // A more complex iteration test.
 TEST_F(StringMapTest, IterationTest) {
   bool visited[100];